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Homework 0: Units & Basic Maths skills
1. State the standard units that are used for the following physical quantities:
Some units are stated with prefixes that mean a specific multiple.
You need to be able to convert such units back to standard units.
The table gives the names, symbols and multiples of the prefixes:
2. Convert the following quantities into appropriate standard units:
a) 900 g
= 0.9 kg
b) 150 g
= 0.15 kg
c) 75,000 mg
= 0.075 kg
d) 90 km
= 90,000 m
e) 377 mm
= 0.377 m
f) 7 minutes
= 420 s
g) 3 hours
= 10,800 s
h) 50 ns
= 0.00000005 s
i) 78 mm/s
= 0.078 m/s
j) 5 km/s
= 5,000 m/s
k) 759 MJ
= 759,000,000 J
l) 89 GJ
= 89,000,000,000 J
m) 0.5 TW
= 500,000,000,000 W
n) 37 mA
= 0.037 A
o) 900 µC
= 0.0009 C
p) 100 kV
= 100,000 V
q) 78 MΩ
= 78,000,000 Ω
r) 500 mm2
= 0.0005 m2
s) 47 cm3
= 0.000047 m3
t) 3.7 g/cm3
= 3,700 kg/m3
Name Nano- Micro- Milli- Centi- Kilo- Mega- Giga- Tera-
Symbol n µ m c k M G T
Multiplier 10-9 10-6 10-3 10-2 103 106 109 1012
a) Mass kilograms, kg
b) Distance / height metres, m
c) Time seconds, s
d) Speed
e) Temperature degrees Celsius, ºC
f) Energy joules, J
g) Power watts, W
h) Electric current amps, A
i) Charge flow coulombs, C
j) Potential difference volts, V
k) Resistance ohms, Ω
l) Area metres squared, m2
m) Volume metres cubed, m3
n) Density kilograms per metre cubed, kg/m3
metres per second, m/s
2
7. A cement factory takes in 300 tonnes of raw materials each day. The cement is produced
in 25 kg sacks. 1 tonne = 1000 kg.
Calculate how many sacks the factory could produce each day.
300 tonnes = 300,000 kg
Number of sacks = 300,000 ÷ 25
Number of sacks = 12,000
8. An ice cube floats in water, because it is less dense than the water.
The total volume of the ice cube is 15 cm3.
Only 1.5 cm3 of the volume of the ice is above the level of the water.
Calculate the percentage of the total volume of the ice that is below the water level.
Volume below surface of water = 15 - 1.5 = 13.5 cm3.
As a percent: (13.5 ÷ 15) x 100 = 90 %
Percentage volume = 90 %
9. A student was using a stopwatch to measure the time taken for a toy car to travel down a
ramp. The following times were recorded for her five repeat measurements:
1.56 s, 1.75 s, 1.58 s, 1.65 s, 1.71 s.
(a) Calculate the mean of the five time measurements.
The mean is the total of all the measurements, divided by the number of measurements.
Mean = (1.56 + 1.75 + 1.58 + 1.65 + 1.71) ÷ 5
mean = 1.65 s
(b) Calculate the range of the five time measurements
The range is found by subtracting the lowest value from the highest.
Range = 1.75 - 1.56
range = 0.19 s
(c) Calculate the uncertainty in time measurements
The uncertainty is found by halving the range.
Uncertainty = 0.19 ÷ 2
uncertainty = 0.095 s
3
Homework 1: Energy
1. A blender transfers energy usefully into which energy store?
The kinetic energy store of the blades.
The elastic potential energy store of the blades.
The magnetic energy store of the blades.
2. The amount of energy transferred by an appliance depends on…
… its power and size.
… its power and mass.
… its power and the time it is on.
3. What happens to the amount of energy in a car’s kinetic energy store when the car slows
down?
It remains the same.
It decreases as some energy is destroyed.
It decreases because some energy is transferred into other energy stores.
4. Which of these is a disadvantage of using solar cells to generate electricity?
They are unreliable, because of the weather.
The produce CO2 when running.
They destroy wildlife habitats.
5. When an object falls from a height, the maximum energy transferred to its kinetic energy
store is equal to…
… the energy transferred to its gravitational potential energy store.
… the energy transferred away from its gravitational potential energy store.
… the energy transferred away from its thermal energy store.
6. Energy is conserved, this means it can be transferred usefully, stored or dissipated.
What does dissipated mean?
Dissipated energy is when it is transferred to the surroundings, usually in the
form of thermal energy.
4
Kinetic energy = 1/2 x mass x speed2
7. A go-kart travels on a straight track at 8.5 m/s. The combined mass of the driver and go-
kart is 160 kg. Calculate the total kinetic energy of the driver and go-kart.
K.E. = 0.5 x 160 x 8.5 x 8.5
……………………………………………………………………………………………………….
Kinetic energy = 5,780 J
8. A different go-kart travels on the straight track at 10.0 m/s. The total kinetic energy of
this go-kart and its driver is 6,500 J. Calculate the total mass of go-kart and driver.
6,500 = 0.5 x mass x 10.0 x 10.0
Mass = 6,500 ÷ 50.0 = 130
Total mass = 130 kg
9. A third go-kart and driver have a total kinetic energy of 4.8 kJ and a combined mass of
150 kg. Calculate the speed of the third go-kart.
4,800 = 0.5 x 150 x speed2
Speed2 = 4,800 ÷ 75 = 64
Speed = √64
Speed = 8.0 m/s
10. A tennis ball has a mass of 60 g, and is served with a speed of 65 m/s. A cricket ball has a
mass of 150 g and is delivered with a speed of 34 m/s. Using calculations, show which ball
has the greater amount of kinetic energy.
Tennis ball: K.E. = 0.5 x 0.06 x 65 x 65 = 126.75 J
Cricket ball: K.E. = 0.5 x 0.15 x 34 x 34 = 86.7 J
The tennis ball has more kinetic energy.
……………………………………………………………………………………………………….
11. Describe all the energy transfers that take place during a roller-coaster ride.
Your description should include all the key-words from the box.
At the start the roller-coaster gains gravitational
potential energy as it is winched up to its highest point.
The coaster then drops along the track speeding up;
energy is transferred from the gravitational potential store
to the kinetic store.
Some energy is dissipated to the surroundings,
because of friction between the wheels and the track, and
because of air resistance.
Dissipated energy increases the thermal energy store
of the surroundings.
Key-words:
Gravitational potential
energy
Kinetic energy
Thermal energy
Friction
Air resistance
Dissipated
Surroundings
5
Homework 2: Energy
1. What is the name of a system in which there is no net change in the total energy?
A closed system.
An open system.
A mechanical system.
2. 800 J of energy is supplied to a toaster with an efficiency of 25%. What is the useful
output of the toaster?
100 J.
200 J.
800 J.
3. When a racket hits a ball, energy is transferred from the racket’s kinetic energy store to
the ball’s kinetic energy store. The energy is transferred...
… by heating.
… electrically.
… mechanically.
4. A toaster has a power of 4 W. How much energy will the toaster transfer in one minute?
4 J.
60 J.
240 J.
5. Which of these is a disadvantage of using wind turbines to generate electricity?
They can cause noise pollution.
They release greenhouse gases like CO2 when running.
They produce dangerous waste that is difficult to dispose of.
6. Fill in the gaps using the words in bold:
Power is the rate at which energy is transferred or work is done.
An energy transfer of 1 J per second is equal to 1 W of power.
energy
work
second
power
transfer
6
Change in gravitational = mass x gravitational field x change in height
potential energy strength
7. A brick has a mass of 1.5 kg. Near the surface of Earth the strength of the gravitational
field is 9.8 N/kg. Calculate the gain in the brick’s gravitational potential energy if it is
lifted up by 1.5 m.
G.P.E. = 1.5 x 9.8 x 1.5 = 22.05 J
……………………………………………………………………………………………………….
Gravitational potential energy = 22.05 J
8. A tennis ball gains 4.9 J of gravitational potential energy when hit to a height of 10 m.
Calculate the mass of the tennis ball. (Use g = 9.8 N/kg)
4.9 = mass x 9.8 x 10
Mass = 4.9 ÷ 98
Mass = 0.05 kg
9. On Earth, g = 9.8 N/kg. A spacecraft at a height of 200 m above Earth’s surface has
2,940 kJ of gravitational potential energy.
The same spacecraft at a height of 100 m above the surface of the Moon has 240 kJ of
gravitational potential energy.
Calculate the gravitational field strength on the Moon.
(On Earth) 2,940,000 = mass x 9.8 x 200
Mass = 2,940,000 ÷ (9.8 x 200) = 1,500 kg
(On Mars) 240,000 = 1,500 x gravitational field strength x 100
Gravitational field strength = 240,000 ÷ 150,000 = 1.6
……………………………………………………………………………………………………….
Gravitational field strength on the Moon = 1.6 N/kg
10. Describe all the energy transfers that take place during a rocket launch into orbit.
Your description should include all the key-words from the box.
Before launch the rocket is full of fuel and so has a large
store of chemical energy. During launch the chemical
energy is transferred to the gravitational potential energy
store as the rocket increases in height, and to the kinetic
energy store as the speed of the rocket increases.
Large amounts of energy are also dissipated to the
surroundings as thermal energy, because of air resistance
and the large amounts of thermal energy in the exhaust
gases of the rocket.
Key-words:
Gravitational potential
energy
Kinetic energy
Chemical energy
Thermal energy
Air resistance
Dissipated
Surroundings
7
Homework 3: Energy
1. Electric heater A has a power rating of 1.5 kW. Electric heater B has a power rating of
880 W. Which heater transfers more energy in 5 hours?
Heater A.
Heater B.
2. The rate of energy transfer from a house can be reduced by...
… having walls and windows with a low thermal conductivity.
… having walls and windows with a high thermal conductivity.
3. Pick a suitable option that can be used to improve the efficiency of a battery-powered
toy car.
Insulate the car.
Use a larger battery to increase the input energy to the car.
Lubricate any moving parts in the car.
4. When a rock rolls down a hill, some energy in its gravitational potential energy store is
transferred to other stores. Which of these stores is energy not transferred to?
The rock’s kinetic energy store.
The rock’s chemical energy store.
The thermal energy store of the surroundings.
5. A cannon uses explosives to launch a ball into the air. Which is a wasteful energy
transfer that occurs when the cannon is fired?
Chemical energy store of explosives to the kinetic energy store of the ball.
Chemical energy store of explosives to the gravitational potential energy of the ball.
Chemical energy store of explosives to the thermal energy store of the ball.
6. Describe two problems with generating electricity using nuclear power.
1. Radioactive waste is produced, which is difficult to dispose of safely.
2. It’s expensive to set up and close down nuclear power stations.
3. There is a risk of radiation leaks and catastrophes, which will harm the
environment.
8
(extension is in metres)
7. An steel spring has a spring constant of 2.5 N/m. The spring is stretched so that it is 5 cm
longer than its original length. Calculate the elastic potential energy store of the spring.
E.P.E. = 0.5 x 2.5 x 0.05 x 0.05 = 0.003125 J
……………………………………………………………………………………………………….
Elastic potential energy = 0.0031 J (2s.f.)
8. An elastic band is stretched by 0.80 m, so that it is storing 6.4 J of elastic potential
energy. Calculate spring constant of the elastic band.
6.4 = 0.5 x k x 0.8 x 0.8
k = 6.4 ÷ (0.5 x 0.8 x 0.8) = 20
Spring constant = 20 N/m
9. A person has a mass of 100 kg. They lay on a bed and they cause all of the 1000 identical
springs in the mattress to compress by the same amount, storing a total elastic potential
energy of 20 J. Each spring has a spring constant of 25 N/m. Calculate the distance that
the person compresses the springs when laying on the bed.
All springs are storing 20 J, so one spring is storing (20 ÷ 1000) = 0.02 J
0.02 = 0.5 x 25 x e2
e2 = 0.02 ÷ ( 0.5 x 25) = 0.0016
e = √0.0016 = 0.04
……………………………………………………………………………………………………….
Compression = 0.04 m
10. Describe all the energy transfers that take place during a bungee jump. Your descrip-
tion should include all the key-words from the box.
The jumper starts with a maximum amount of gravitational
potential energy. As they fall, they speed up and so their
kinetic energy store increases, and their gravitational potential
energy decreases. As the bungee chord stretches its elastic po-
tential energy store increases, and the jumper’s fall slows and
so their kinetic energy store decreases. Throughout the jump,
because of air resistance, energy is dissipated so the thermal
energy store of the surroundings increases.
Key-words:
Gravitational potential
energy
Kinetic energy
Elastic potential energy
Thermal energy
Air resistance
Dissipated
Surroundings
9
Homework 4: Energy
1. If a moving object doubles its speed, what happens to the energy in its kinetic energy
store?
It stays the same.
It doubles.
It goes up by a factor of 4.
2. Two materials with the same mass and different specific heat capacities are cooled by
10ºC. Which material emits more energy?
The material with the higher specific heat capacity.
The material with the lower specific heat capacity.
3. When a spring is compressed, which of these energy stores is energy transferred to?
The spring’s elastic potential energy store.
The spring’s nuclear energy store.
The spring’s magnetic energy store.
4. Power is the...
… conservation of momentum.
… energy of a moving object.
… rate of doing work.
5. Two garages of equal size and shape have walls made of the same material. One garage
has thicker walls than the other. They are heated to the same temperature then left to
cool. Which garage will cool the quickest?
The one with the thicker walls.
The one with the thinner walls.
6. Describe the two useful energy transfers in an electric hairdryer.
A hairdryer transfers energy electrically from the mains to the thermal energy
store of the hairdryer’s heater and to the kinetic energy store of the fan blades.
The heater in turn transfers energy to the thermal energy store of the air, and
the fan blades transfer energy to the kinetic energy store of the air.
10
(mass must be in kilograms)
7. A kettle is used to boil 0.75 kg of water, by increasing the temperature of the water from
10ºC to 100ºC. The specific heat capacity of water is 4200 J/kgºC. Calculate the amount
of thermal energy that has been transferred to the water.
E = 0.75 x 4200 x (100-10) = 283,500 J
……………………………………………………………………………………………………….
Increase in thermal energy = 283,500 J
8. A 0.5 kg block of copper is supplied with 3.9 kJ of thermal energy. The temperature of the
metal increases by 20ºC. Calculate the specific heat capacity of copper.
3.9 kJ = 3,900 J
3,900 = 0.5 x c x 20
c = 3,900 ÷ (0.5 x 20) = 390
Specific heat capacity = 390 J/kgºC
9. Solid aluminium has a specific heat capacity of 900 J/kgºC and brass has a specific heat
capacity of 600 J/kgºC. A 0.75 kg block of aluminium and a 1 kg block of brass are both at
room temperature and are both supplied with 10 kJ of thermal energy.
Using calculations, show which block has the larger increase in temperature.
Aluminium: 10,000 = 0.75 x 900 x Δθ
Δθ = 10,000 ÷ (0.75 x 900) = 14.81 ºC
Brass: 10,000 = 1.0 x 600 x Δθ
Δθ = 10,000 ÷ (1.0 x 600) = 16.67 ºC
The brass block will have the larger temperature increase.
10. Describe all the energy transfers that take place while a moving car comes to a stop.
Your description should include all the key-words from the box.
The car is moving and so has kinetic energy. To stop the
driver applies the brakes, which apply a friction force on
the wheels. Because of friction, work is done and so energy
transferred from the kinetic energy store of the car into the
thermal energy store of the brakes.
The brakes then dissipate their thermal energy by heating
up the surroundings.
Key-words:
Kinetic energy
Thermal energy
Work done
Friction
Dissipated
Surroundings
11
Homework 5: Energy
1. We continue to use non-renewable energy resources despite their negative impact on the
environment. Which of the following is a possible reason for this?
Non-renewables will never run out.
Non-renewable resource are more reliable than renewable alternatives.
Renewable alternatives are more harmful to the environment.
2. Motor 1 and motor 2 each lift objects of equal weight. They both have the same power
rating, but motor 2 lifts the weight in a shorter amount of time. Which motor is more
efficient.
Motor 1.
Motor 2.
3. 250 J of energy is supplied to a fan. The fan transfers 100 J of this energy to useful
energy stores. What is the efficiency of the fan?
0.1
0.4.
0.6.
4. Which is the least reliable method of generating electricity from water?
Tidal power.
Hydroelectricity.
Wave power.
5. A robot has a power output of 50 W. How much energy does it transfer in 10 minutes?
50 J.
5,000 J.
30,000 J
6. State the maximum possible efficiency and explain why there is a maximum efficiency.
The maximum possible efficiency is 100%.
Energy cannot be created, only transferred. Therefore in an energy transfer,
the maximum energy transferred usefully is equal to the total energy transferred.
12
7. A kettle transfers 6.0 kJ of energy to the thermal energy store of its water, but 1,500 J of
energy is dissipated to the surroundings. Calculate the efficiency of the kettle.
Useful = 6000 J. Total = (6000 + 1500) = 7500 J
Efficiency = 6000 ÷ 7500 = 0.8
Efficiency = 0.8 (80%)
8. A motor with an efficiency of 0.6 uses a total of 550 J of energy. Calculate the amount of
useful energy that is transferred by the motor.
0.6 = useful ÷ 550
useful = 0.6 x 550 = 330 J
Useful energy = 330 J
9. A water pump has a useful power output of 75 W. The manufacturer states that the
pump has an efficiency of 0.8. Calculate the power that is supplied to the pump.
0.8 = 75 ÷ power supplied
Power supplied = 75 ÷ 0.8 = 93.75 W
Power supplied = 93.75 W
9. A charger will replenish 450 J of chemical energy into a mobile phone’s battery, while
wasting 150 J of energy. The mobile phone is then used to wirelessly charge a second
phone. The battery of the second phone only receives 300 J of chemical energy in the
process. Calculate the overall efficiency of charging the second phone in this way.
Useful energy transferred to 2nd phone = 300 J
Total energy supplied to whole process = 450 + 150 = 600 J
Efficiency = 300 ÷ 600 = 0.5 (or 50%)
10. Describe and explain how you would increase the efficiency and so the maximum speed of
a gravity powered go-kart. Your answer should include all the key-words from the box.
The body of the go-kart should be made more streamlined to
reduce air resistance. Also lubrication should be applied to
all moving parts in the go-kart to reduce friction.
Both of these will have the effect of reducing the amount of
energy that is dissipated to the surroundings and so the
kinetic energy store of the go-kart will increase meaning the
kart will have a higher top-speed.
Key-words:
Streamlined
Air resistance
Lubrication
Friction
Dissipated
Surroundings
Kinetic energy
13
Homework 6: Electricity
1. True or False? “The resistance of a thermistor is higher when its temperature is higher.”
True.
False.
2. True or False? “Transformers are used to carry electricity all around the country.”.
True.
False.
3. Which of the following is a device that emits light?
LDE
LDR
LED
4. A current of 2 A passes through a device with a resistance of 8 Ω. What is the power of
the device?
16 W.
32 W. P = I2 R = 2 x 2 x 8 = 32 W
128 W.
5. True or False? “Two components connected in parallel will each have the same potential
difference across them.”
True.
False.
6. Describe how friction can cause a neutral object to become positively charged.
Friction can cause negatively charged electrons to transfer from one material
to another.
The object that loses the electrons will become positively charged.
(The object that gains electrons will become negatively charged.)
14
7. While in use, a 1.2 V cell transfers 5.4 kJ of energy. Calculate how much charge passed
through the cell.
5.4 kJ = 5,400 J 5,400 = Q x 1.2
Q = 5,400 ÷ 1.2 = 4,500 C
Charge = 4,500 C
8. 27 C of charge passed through a resistor that had a potential difference of 9 V across it.
Calculate the energy transferred by the resistor.
E = 27 x 9 = 243 J
……………………………………………………………………………………………………….
Energy transferred = 243 J
9. 90 MJ of energy is transferred in a lightning strike, when 15 C of charge passed from the
cloud to the Earth. Calculate the potential difference between the cloud and Earth.
90 MJ = 90,000,000 J 90,000,000 = 15 x V
V = 90,000,000 ÷ 15 = 6,000,000 V
Potential difference = 6,000,000 V
10. 9.0 C of charge passes through a 12 V electric motor, while 8.0 mC of charge passes
through a 15 kV insect zapper. By using calculations, show which appliance transfers
more energy.
Motor: E = 9.0 x 12 = 108 J
Zapper: E = 0.008 x 15,000 = 120 J
The zapper transfers more energy.
11. Explain why car manufacturers electrostatically charge the car bodies and the paint
before it is sprayed. Your answer should include all the key-words from the box.
If the car body is given a positive charge and the paint is
sprayed with a negative charge, then because they are oppo-
sitely charged, the paint will experience a force that attracts
it to the body of the car.
This has two benefits, there will be less waste and it will
reduce cost of paint.
Key-words:
Positive
Negative
Force
Attract
Waste
Reduce cost
15
Homework 7: Electricity
1. Static electricity is caused by the transfer of which particles?
Electrons.
Protons.
Neutrons.
2. In a circuit with a fixed potential difference, what would happen to the current if you
increased the total resistance?
The current would increase.
The current would stay the same.
The current would decrease.
3. Increasing the potential difference of electricity at a constant power…
… increases the energy lost through heating.
… decreases the current flowing.
… increases the rate of flow of charge.
4. True or False? “Potential difference is the work done per unit charge (coulomb) flowing
between two points in a circuit.”
True.
False.
5. A student investigated the relationship between the
length of a conductor and its resistance. The graph
shows the best fit line drawn.
a) Describe the relationship between the length of
conductor and its resistance.
The resistance is directly proportional to the
length of the conductor.
b) Use the graph to estimate the resistance of the same conductor, but when its length
is 60 cm.
The resistance is 4.0 Ω at 30cm long, so at 60cm long the resistance will be 8.0 Ω
16
6. While in use, a cell delivers a current of 0.5 A. The cell is in use for 15 minutes, calculate
the amount of charge that passes through the cell.
Q = 0.5 x 15 x 60 = 450 C
……………………………………………………………………………………………………….
Charge = 450 C
7. 27 C of charge passes through a resistor at a rate of 0.9 A. Calculate the time taken.
27 = 0.9 x t
t = 27 ÷ 0.9 = 30 s
Time taken = 30 s
8. 15 C of charge passes from a storm cloud to the Earth in a lightening strike. The strike
lasts for 0.5 ms, calculate the current of the lightening strike.
0.5 ms = 0.0005 s 15 = I x 0.0005
I = 15 ÷ 0.0005 = 30,000 A
Current = 30,000 A
9. 10 A of current passes through a kettle for 2 minutes.
0.5 A of current passes through a light bulb for half an hour.
By using calculations, show which appliance has more charge flowing through it.
Kettle: Q = 10 x 2 x 60 = 1,200 C
Bulb: Q = 0.5 x 30 x 60 = 900 C
More charge flowed through the kettle.
……………………………………………………………………………………………………….
10. The potential difference – current graph of a filament
bulb is shown in the graph. Explain why the graph
curves as the current increases.
Your answer should include all the key-words from
the box.
As current increases, the temperature of the fil-
ament increases.
As its temperature increases, its resistance increases.
This is shown in the graph as the gradient of the curve
decreases.
(Remember: you DO NOT calculate resistance from the
gradient of the graph.)
Key-words:
Temperature
Resistance
Gradient
17
Homework 8: Electricity
1. What is the name for electric current that is constantly changing direction?
Alternating current (ac).
Direct current (dc).
Switching current (sc).
2. True or False? “In a series circuit, the source potential difference is shared between all
the components.”
True.
False.
3. True or False? “Transmitting electricity at a high potential difference and a low current
is more energy efficient than transmitting at a low potential difference and high current.”
True.
False.
4. True or False? “A static charge can build up when two insulating materials are rubbed
against each other.”
True.
False.
5. Three-core cables have 3 wires inside the outer insulation. Link the names of the wires
to the colours of their insulating coatings.
6. True or False? “The current is the same at any point in a single closed loop of wire that
is connected to a power supply.”
True.
False.
Earth
Live
Neutral
Brown
Blue
Green / Yellow
18
7. 0.25 A of current flows through a resistor when a 12.0 V potential difference is across it.
Calculate the resistance of the resistor.
R = 12.0 ÷ 0.25 = 48.0
……………………………………………………………………………………………………….
Resistance = 48.0 Ω
8. 0.3 A of current flows through a 120 Ω resistor. Calculate the potential difference across
the resistor.
V = I x R
= 0.3 x 120 = 36 V
Potential difference = 36.0 V
9. 1.5 kV of potential difference is across a 4.5 kΩ resistor. Calculate how much current will
flow through the resistor.
1.5 kV = 1,500 V 4.5 kΩ = 4,500 Ω
I = V ÷ R = 1,500 ÷ 4,500 = 0.333
Current = 0.333 A
10. 10 A of current passes through a kettle with a potential difference of 230 V.
0.5 A of current flows through a toy car’s motor with a potential difference of 12.0 V.
By using calculations, show which appliance has the greater resistance.
Kettle: R = 230 ÷ 10 = 23 Ω
Motor: R = 12.0 ÷ 0.5 = 24 Ω
The motor has a greater resistance.
11. The circuit diagram shows two resistors connected in series with a battery.
a) Find the reading on voltmeter V3.
V3 = V1 + V2 = 3 + 2 = 5
Potential difference = 5.0 V
B) Find the total resistance, R, of the circuit.
Rt = R1 + R2 = 6 + 4 = 10
Resistance = 10 Ω
C) Find the reading on the ammeter.
I = V ÷ R = 5.0 ÷ 10 = 0.5
Current = 0.5 A.
19
Homework 9: Electricity
1. Electric current is...
… the driving force that pushes charges around a circuit.
… a measure of how much charges slow down as they flow through a circuit.
… the rate of flow of electrical charge.
2. True or False? “The UK mains electricity supply is direct current.”
True.
False.
3. In the UK, what is the typical potential difference between the live wire and the earth
wire in an electrical appliance?
230 V.
0 V.
12 V.
4. What type of resistor could be used in a sensing circuit designed to turn on an automatic
night light when it gets too dark?
Diode.
Thermistor.
LDR.
5. The resistance of an ohmic conductor at a constant temperature...
… is higher when larger currents flow through it.
… doesn’t change as the current varies.
… is low when the current flows in one direction, but much higher when current
flows in the reverse direction.
6. Components connected in a parallel circuit will usually receive...
… a fraction of the supply potential difference.
… the same current as any other component in the circuit.
… the full supply potential difference.
20
7. 0.25 A of current flows through a resistor when a 12.0 V potential difference is across it.
Calculate the electrical power supplied to the resistor.
P = V x I = 12.0 x 0.25 = 3.0
……………………………………………………………………………………………………….
Power = 3.0 W
8. A 60 W motor is connected to a battery pack with a potential difference of 15 V.
Calculate the current flowing through the motor.
P = V x I
60 = 15 x I I = 60 ÷ 15 = 4.0
Current = 4.0 A
9. 30 A of current flows through 4.5 kW heater. Calculate the potential difference across
the heater.
P = V x I 4.5 kW = 4,500 W
4,500 = V x 30 V = 4,500 ÷ 30 = 150
Potential difference = 150 V
10. Calculate the power output of a 10 Ω resistor, when 0.5 A of current flows through it.
P = I2 x R
P = 0.5 x 0.5 x 10 = 2.5
Power = 2.5 W
11. A flood light transfers energy at a rate of 640 W, with a resistance of 10 Ω.
A motor rated at 72 W, has a resistance of 2.0 Ω.
By using calculations, show which appliance has more current flowing through it.
Flood light: P = I2 x R 640 = I2 x 10 I2 = 640 ÷ 10 = 64
I = √(64) = 8.0 current = 8.0 Amps
……………………………………………………………………………………………………….
Motor: P = I2 x R 72 = I2 x 2 I2 = 72 ÷ 2 = 36
I = √(36) = 6.0 current = 6.0 Amps
The flood light has more current flowing through it.
21
Homework 10: Particle Model of Matter
1. What are the units for density?
kg/m2.
kg/m3.
m3/kg.
2. True or False? “Liquids are generally denser than solids and gases.”
True.
False.
3. The internal energy of a system is equal to…
… the total kinetic energy that its particles have in their kinetic energy stores.
… the total energy that its particles have in their potential energy stores.
… the total energy that its particles have in their kinetic and potential energy stores.
4. Which of the following is not caused by increasing the energy of the particles in a liquid?
Increase in temperature.
Boiling.
Condensing.
5. What happens to the mass of a substance when it changes from a solid to a liquid?
It increases.
It decreases.
It stays the same.
6. What quantity gives the energy released when 1 kg of a liquid becomes a solid with no
change in temperature?
Specific latent heat of vaporisation.
Specific latent heat of fusion.
Specific heat capacity.
22
7. A basket ball has a mass of 600 g. The ball’s volume is 0.015 m3. Calculate the density of
the basket ball.
Mass = 600g = 0.6 kg Volume = 0.015 m3.
Density = mass ÷ volume = 0.6 ÷ 0.015 = 40.0
Density = 40.0 kg/m3.
8. An aluminium block has a mass of 5 kg. The density of aluminium is 2.5 kg/m3. Calcu-
late the volume of the aluminium block.
Density = mass ÷ volume
2.5 = 5 x volume volume = 2.5 ÷ 5.0 = 0.5
Volume = 0.5 m3.
9. At sea-level, a weather balloon has a volume of 1,500 m3. The density of helium gas at
sea-level is 0.5 kg/m3. Calculate the mass of helium inside the weather balloon.
Density = mass ÷ volume
0.5 = mass ÷ 1,500 mass = 0.5 x 1,500 = 750
Mass = 750 kg.
10. The density of water is 1000 kg/m3.
A wooden block measures 20 cm by 30 cm by 40cm, and it has a mass of 0.216 kg.
By using calculations, show whether the block of wood will float or sink in water.
20cm = 0.2m, 30cm = 0.3, 40cm = 0.4m
Volume = 0.2 x 0.3 x 0.4 = 0.024 m3.
Density of block = mass ÷ volume = 0.216 ÷ 0.024 = 9.0 kg/m3.
The density of the block is much less than water so it will float.
11. Describe how the density of a solid object of known mass can be
measured using a eureka can.
Your answer should include all the key-words from the box.
Fill a eureka can to the spout with water.
Submerge the solid object in the can and collect all of the
displaced water.
Measure the volume of the displaced water using a measuring
cylinder. This is equal to the volume of the object,
You can then divide the mass of the object by its volume to
calculate its density.
Key-words:
Fill
Submerge
Collect
Displaced
Volume
Mass
Divide
23
Homework 11: Particle Model of Matter
1. What will happen to the pressure of a fixed volume of gas if its temperature is increased?
It will decrease.
It will increase.
It will stay the same.
2. True or False? “Doing work on a gas decreases the internal energy off the gas.”
True.
False.
3. Changes of state are different to chemical changes because…
… changes of state can be reversed to recover the original properties of the material.
… changes of state result in the creation of new substances.
… changes of state cannot happen to gases.
4. Which of the following statements about gas particles is not true?
Gas particles travel with a range of high speeds.
Gas particles travel in random directions.
Gas particles have less energy than liquid and solid particles.
5. In which direction does the pressure of a gas in a container produce a net force?
At right angles to the walls of the container.
Parallel to the walls of the container.
Directly upwards.
6. What is the specific latent heat of vaporisation?
The amount of energy needed to melt 1kg of a substance.
The amount of energy needed to boil 1kg of a substance.
The amount of energy released when 1kg of a substance condenses.
24
7. Calculate the energy needed to melt 500g of ice. The specific latent heat of fusion for ice
is 334 kJ/kg. (Be very carful with units)
Mass = 500 g = 0.5 kg L = 334 kJ/kg = 334,000 J/kg
E = mL = 0.5 x 334,000 = 167,000 J
Energy = 167,000 J
8. A solid gold bar of mass 1kg is already at its melting point. A further 8 kJ of energy is
supplied to the bar. Calculate how much mass melts. The specific latent heat of fusion of
gold is 64 kJ/kg.
E = m L 8 kJ = m x 64 kJ/kg (kJ used on both sides of = sign)
m = 8 ÷ 64 = 0.125 kg
Mass = 0.125 kg
9. A kettle brings 1kg of water to its boiling point. The kettle is faulty and doesn’t switch
off. The kettle supplies a further 45kJ of energy, boiling off a mass of 20g of water.
Calculate the specific latent heat of vaporisation of water.
Mass = 20 g = 0.02 kg
E = m L So L = E ÷ m L = 45 kJ ÷ 0.02 kg
Specific latent heat = 2,250 kJ/kg
10. Ethanol has a specific latent heat of vaporisation of 855 kJ/kg. Calculate the energy
required to boil 600g of ethanol.
Mass = 600g = 0.6 kg L = 855 kJ/kg = 855,000 J/kg
E = m L = 0.6 x 855,000 = 513,000 J
Energy = 513,000 J
11. Describe how the arrangement and movement of particles is different in a solid, a liquid
and a gas.
Your answer should include all the key-words from the box.
In a solid the particles are arranged in a regular pattern and
can only vibrate around a fixed position.
In a liquid the particles are still touching each other, but can
flow past each other. They can move in random directions and
they have a range of speeds.
In a gas the particles are far apart from each other on average.
This is why gases can be compressed.
The particles move in all directions randomly, with a range of
speeds.
Key-words:
Regular
Vibrate
Fixed
Random
Range of speeds
Far apart
Touching
The units ask for L in kJ
per kg of mass.
25
Homework 12: Atomic Structure
1. Which of these is the most hazardous outside of the body?
Alpha particles. (Alpha particles are stopped by your skin.)
Beta and gamma radiation.
All types of radiation are equally hazardous.
2. True or False? “People living in different parts of the UK will be exposed to different
amounts of background radiation.”
True.
False.
3. What is the name for atoms with the same number of protons but different numbers of
neutrons?
Ions.
Isomers.
Isotopes.
4. True or False? “The results of the alpha particle scattering experiment led to the
development of the plum pudding model of the atom.”
True.
False.
5. The count rate of a radioactive sample falls from 130 Bq to 65 Bq in 15 minutes.
What is its half-life?
15 minutes.
30 minutes.
1 hour.
6. Describe the difference between an atom and an ion.
An atom is overall neutral, because it has an equal number of electrons and protons.
An ion has an overall charge, because it is an atom that has gained or lost electrons.
26
7. The decay of phosphorus-32 is shown below.
Complete the equation by writing in the missing atomic number and mass number.
8. Use the graph below to work out the half-life of the radioactive sample.
Half-life = 4 Hours
9. The count rate of a radioactive sample is 500 Bq. The half-life of the sample is 4 hours.
Calculate what the count rate would have been if it had been measured 12 hours earlier.
12 ÷ 4 = 3 half-lives. So the activity is going to halve 3 times.
……………………………………………………………………………………………………….
500 x 0.5 x 0.5 x 0.5 = 62.5
Count rate = 62.5 Bq
10. Describe the difference between irradiation and contamination
Your answer should include all the key-words from the box.
When an object is exposed to (ionising) radiation it is said to
have been irradiated.
(Irradiation can be useful in sterilising surgical equipment or
to kill bacteria on food to increase its shelf-life.)
Contamination is when unwanted radioactive material gets on
or inside an object (or person).
(Protective clothing is worn in contamination zones, so that
the person inside does not get contaminated. The protective
clothes will need to be scrubbed down or disposed of. )
Key-words:
Exposed
Radiation
Unwanted
Radioactive
On / inside
32
16
27
Homework 12a: Atomic Structure (Physics only)
1. What particle can trigger nuclear fission when it is absorbed by a uranium nucleus?
Electron.
Proton.
Neutron.
2. True or False?
“Nuclear fusion is when two small nuclei join together forming a larger nucleus.”
True.
False.
3. A radioactive tracer is given to a patient so a doctor can image an internal organ.
What type of radiation should the tracer emit?
Alpha radiation.
Beta radiation.
Gamma radiation.
4. The same radioactive tracer from Q3, should have a half-life of approximately ...
… 2-5 minutes. (too short, will have decayed before scan takes place.)
… 1-2 hours.
… 3-4 weeks. (too long, the activity will be inside the patient for months.)
5. Which statement is not true about nuclear fission reactors?
Control rods are used to absorb the surplus neutrons given out during fission.
Water acts as a moderator, by slowing down fission neutrons.
An uncontrolled chain-reaction is used to maintain a steady power output.
6. Complete the follow nuclear fusion equation.
H H He 1
1 2 +
1 2
3
28
7. Uranium-235 will fission when it absorbs a neutron.
Complete the equation by writing in the missing atomic number and mass number.
8. The table to the right gives some
of the sources of background
radiation in the UK.
(1µSv = one millionth of a 1 Sv.)
The risk to the average person
in the UK from background
radiation is about the same as
the risk from road traffic, which
causes around 10 deaths per
100,000 people each year.
Use data from the table to
evaluate whether measures such as avoiding air travel would reduce the risk from
background radiation.
The radiation dosage for air travel (and nuclear testing and power) is many
times smaller than the radiation dosage from sources that cannot be avoided,
such like cosmic rays, food and drink, and radioactivity in the air.
In my view people who choose not to travel by air, because of radiation dosage
are not reducing the risk to them by a measurable amount and so I would
advise them to not give up air travel.
(A better reason to give up air travel is because of the greenhouse gases that
are emitted into the atmosphere by air travel.)
9. The count rate of a radioactive sample fell from 6400 Bq to 100 Bq in 66 minutes.
Calculate the half-life of the sample.
6400 is halved 6 times to drop to 100. So 6 half-lives have passed.
6400 x 0.5 x 0.5 x 0.5 x 0.5 x 0.5 x 0.5 = 100
66 minutes ÷ 6 = 11 minutes
Half-life = 11 minutes
n U Cs 0
1 235 + 143
55 Rb 37 + + 3 n
0
1
92
89
29
Homework 13: Atomic Structure
1. When a radioactive nucleus emits a beta particle ...
… the mass number drops by four.
… the atomic number drops by two.
… the atomic number increases by one.
2. True or False? “The longer the half-life of a radioactive sample, the sooner it will stop
being radioactive.”
True.
False.
3. Which type of radiation can penetrate the furthest in to materials?
Alpha.
Beta.
Gamma.
4. True or False? “The plum pudding model suggested that the atom was a sphere of posi-
tively charged mass with small negative electrons stuck in it.”
True.
False.
5. Which of these statements is correct?
Background radiation is around us all the time.
People must be shielded from all background radiation.
Background radiation is only caused by fallout from nuclear weapons tests.
6. Describe how the orbit of an electron around an atom’s nucleus changes when the electron
absorbs an electromagnetic wave.
If an electron in orbit around a nucleus absorbs an electromagnetic wave it can
rise up to a higher energy level (electron shell). If the energy of the wave is high
enough the electron can leave the atom completely, ionising the atom (turning it into
an ion.).
30
7. The decay of uranium-238 by alpha-emission is shown below.
Complete the equation by writing in the missing atomic number and mass number.
8. A radioactive sample has account rate of 960 Bq. Its half-life 30 minutes.
How long will it take for the count rate to drop to 120 Bq.
960 x 0.5 x 0.5 x 0.5 = 120 960 is halved 3 times to get 120.
……………………………………………………………………………………………………….
Each half life is 30 minutes. So 3 x 30 = 90
Time = 90 Minutes
9. A sample of ancient wood was carbon-dated and found to have 25% of the count rate of an
equal mass of living wood. The half-life of radioactive carbon is 5600 years. Calculate
how old the sample of ancient would must be.
100% x 0.5 x 0.5 = 25% So 2 half-lives have passed since the wood was alive.
……………………………………………………………………………………………………….
Each half-life is 5600 years. So 2 x 5600 = 11,200
Age of wood sample = 11,200 Years
10. In the early 20th century the plum pudding model of the atom was replaced by the
nuclear model of the atom.
Explain why the plum pudding model was replaced by the nuclear model.
Your answer should include all the key-words from the box.
In the alpha-particle scattering experiment, most of the
alpha particles passed straight through the thin gold foil.
This shows that the atoms are mostly empty space.
Some alpha particles were deflected through large angles
(greater the 90º). This shows that at the centre of atoms
there is a small positively charged region where most of the
mass of the atom is located.
The evidence from this experiment completely disagreed
with the plum-pudding model of the atom, which had
positively charged mass spread evenly with negatively
charged electrons embedded within.
Key-words:
Alpha scattering
Straight though
Empty space
Deflected
Large angles
Positively charged
Mass
Charge
Spread evenly
U Th 238
90 + He 92
234
2
4
31
Homework 14: Paper 1 Mixed Topics
1. The amount of energy needed to raise the temperature of 1 kg of a substance by 1°C is ...
… its boiling point.
… its specific heat capacity.
… its specific latent heat.
2. True or False? “A live wire can still be dangerous even when a switch in the mains circuit
is open.”
True.
False.
3. What is the power of a device that transfers 20 J of energy in 5 seconds?
4 W.
10 W.
100 W.
4. True or False? “The atomic number of an alpha particle is 4.”
True.
False. (Atomic number = 2, mass number = 4)
5. Which of the following equations correctly shows the relationship between the gravitation-
al potential energy of an object, Ep, the object’s mass, m, the gravitational field strength, g,
and the object’s height, h?
6. Describe what happens to the total resistance of a circuit and therefore what happens to
the total current flowing in a circuit when a resistor is added in parallel.
Adding a resistor in parallel reduces the overall resistance, because another path for
current to flow is available. If the total resistance has decreased, the total current
flowing will have increased.
32
7. A car’s headlights are switched on. The headlights are connected in parallel in an
electrical circuit. One light goes out when its bulb blows.
Explain why both lights don’t go out when one bulb blows?
In a parallel circuit, each component is connected separately to the power
supply. When one bulb blows, only that part of the circuit is broken, so
current can still flow to the other bulb and so it stays on.
8. (a) An electric current of 3.0 A flows through a bulb for 45 seconds.
Calculate the amount of charge that has flowed through the bulb in that time.
Charge = current x time
Charge = 3.0 A x 45 s = 135 C
Charge = 135 C
(b) The potential difference across the bulb is 12.0 V.
Calculate the energy that has been transferred by the bulb.
Energy = charge flow x potential difference
Energy = 135 C x 12.0 V = 1,620 J
Energy = 1,620 J
9. (a) A brick with a mass of 1.5 kg falls from a height of 5.1 m onto the floor.
The gravitational field strength is 9.8 N/kg.
Calculate the decrease in gravitational potential energy of the brick during the fall.
ΔE = mass x gravitational field strength x height change
ΔE = 1.5 x 9.8 x 5.1 = 74.97 J
Gravitational potential energy = 74.97 J
(b) If we assume that there is no air resistance, then all the gravitational potential
energy of the brick will have transferred into its kinetic energy store.
Calculate the speed that the brick will have just before it hits the floor.
Round your answer to 2 significant figures.
Ek = 0.5 x mass x speed2
74.97 = 0.5 x 1.5 x speed2
speed2 = 74.97 ÷ (0.5 x 1.5) = 99.96
speed = √99.96 = 9.9979 = 10 m/s (2s.f.)
Speed = 10 m/s
33
Homework 15: Paper 1 Mixed Topics
1. Which is true in the nuclear model of the atom?
The nucleus in the atom is uncharged.
The atom is a ball of positive charge with electrons evenly distributed throughout.
The mass of the atom is concentrated at its centre.
2. True or False? “The pressure of a gas held at constant volume decreases if the
temperature is decreased.”
True.
False.
3. What happens to the resistance of a filament lamp as its temperature increases?
It increases.
It decreases.
It stays the same.
4. True or False? “After a substance is condensed, it can be sublimated to recover its
original properties.”
True. (Some substances can condense from a gas straight to a solid.)
False.
5. Which of the following correctly describes the energy source used in geothermal power?
Energy released from controlled nuclear fission reactions.
Energy released by burning plant products.
Energy released by hot rocks deep in the ground.
6. Describe what the internal energy of a system is.
The internal energy of a system is the total of all the kinetic energy and potential
energy of all the particles making up the object, substance, or system.
Increasing temperature, increases the internal kinetic energy.
Changing state of matter, changes the internal potential energy of the particles.
34
7. A student has a source of radiation that emits one of the three types of ionising nuclear
radiation. She places the source opposite a Geiger-Muller tube and detector and records
the count rate. She then places a sheet of paper between the source and the detector and
records the count rate, and then repeats this with a sheet of aluminium instead of paper.
Describe how her results will allow her to work out which type of radiation is emitted by
the source.
If the count-rate drops significantly when the paper is used, then the source
emits alpha particles.
If the count-rate reduces significantly when the aluminium plate is used, but
not when the paper is used, then the source emits beta particles.
If the count rate is not reduced significantly by either the paper or the
aluminium, then the source emits gamma rays.
8. A circuit diagram is shown:
Identify the component labelled X.
Thermistor
The component X has a resistance of 3.0 Ω.
(a) Calculate the current passing through
the circuit.
Total resistance = 2.0 + 3.0 = 5.0 Ω
Total current = Total potential difference ÷ Total resistance
Current = 9.3 ÷ 5.0 = 1.86 A
Current = 1.86 A
(b) Calculate the potential difference across the 2.0 Ω resistor.
Potential difference = current x resistance
Potential difference = 1.86 A x 2.0 Ω
Potential difference = 3.72 V
35
Homework 16: Paper 1 Mixed Topics
1. What are the units for specific heat capacity?
J / kg ºC.
kg / J ºC.
ºC / J kg.
2. True or False? “Two isotopes of carbon will have the same number of neutrons but a
different number of protons.”
True.
False. Isotopes of the same element have the same number of protons.
3. What happens to the resistance of an LDR as the intensity of light shone on it increases?
It increases.
It decreases.
It stays the same.
4. True or False? “Biofuels are made over millions of years from dead organic material.”
True.
False. Biofuels are made from living or recently living organisms.
5. Electricity is transferred across a step-up transformer to...
… increase the potential difference for transmission from power stations.
… increase its potential difference for domestic use.
… increase its current for transmission from power stations.
6. An electric pencil sharpener has an efficiency of 75%. Calculate the amount of energy that
is usefully transferred by the sharpener if 560 J in total is supplied to it.
75% = 0.75
Efficiency = useful energy transferred ÷ total energy transferred
0.75 = useful ÷ 560
Useful = 0.75 x 560 = 420 J Energy = 420 J
36
7. A student uses a heater to supply 22 000 J of energy to a material with a mass of 540 g.
The material has a specific heat capacity of 950 J/kgºC.
Calculate the temperature increase of the material.
540 g = 0.54 kg
22,000 = 0.54 x 950 x temp. change
temp. change = 22,000 ÷ ( 0.54 x 950) = 42.885 = 42.9 (3s.f.)
Temperature increase = 42.9 ºC.
8. The equation below shows the alpha decay of an isotope of americium. Complete the
equation by writing the missing atomic number and mass number of the product.
9. The cube shown in the figure has a density of 8800 kg/m3.
Calculate the mass of the cube in kilograms.
4.0 cm = 0.04 m
Volume = 0.04 x 0.04 x 0.04 = 0.000064 m3.
Mass = density x volume
Mass = 8800 x 0.000064 = 0.5632 kg
Mass = 0.5632 kg.
237
93
37
Homework 17: Paper 1 Mixed Topics (Physics only)
1. Which of the following is equal to the efficiency of a device?
total power input ÷ useful power output.
useful power output ÷ total power input.
total power input x useful power output
2. True or False? “The pressure of a fixed mass of gas held at a constant temperature, is
inversely proportional to its volume.”
True.
False.
3. What happens in nuclear fusion?
One heavy nucleus emits a beta particle.
One heavy nucleus splits into two lighter nuclei after absorbing a neutron.
Two light nuclei combine to form a heavier nucleus.
4. True or False? “A charged particle’s electric field is weaker closer to the charged particle.”
True.
False.
5. Why does increasing the volume in which a gas is contained at a constant temperature
cause the pressure to decrease?
The particles hit the walls of the container less often.
The particles hit the walls of the container with less force.
The particles hit the walls of the container at a slower speed.
6. An apple with a mass of 0.1 kg hangs 2m above the ground. Assuming the gravitational
field strength is 9.8 N/kg, calculate the amount of energy that the apple has in its
gravitational potential energy store.
E = m g h
E = 0.1 x 9.8 x 2.0 = 1.96 J
Energy = 1.96 J
38
7. A sealed container with a moveable lid is filled with gas. The gas is compressed so that it
has a volume of 290 cm3. The gas has a pressure of 160 kPa. The gas is then allowed to
expand until its pressure reaches 110 kPa. If the temperature of the gas remains
constant, calculate the new volume of the gas in cm3.
160 x 290 = 46,400 kPa cm3 (this stays constant)
new pressure x new volume = same constant
110 x new volume = 46,400
New volume = 46,400 ÷ 110 = 421.818 = 422 cm3 (3s.f.)
Volume = 422 cm3.
8. Cancer is a condition in which tissue in the body grows uncontrollably.
State why ionising radiation is used in cancer treatment and describe how it is used.
Ionising radiation can kill cells. The radiation is targeted at the tumour to
kill the cancer cells and control their growth. This sometimes involves
targeting the tumour from multiple directions to reduce the dosage on health
tissue.
9. Describe fully what happens during nuclear fission.
Your answer should include all the key-words from the box.
During nuclear fission, a large nucleus (like uranium-235)
absorbs a neutron (to become uranium-236).
This nucleus splits into two smaller nuclei ( of similar size).
In addition 2 or 3 neutrons are also released.
This reaction releases a large amount of energy.
The 2 or 3 fission-neutrons can go on to be absorbed by
other uranium nuclei, which in turn go through the same
reaction. This is called a chain-reaction.
( In a nuclear reactor, control rods are used to absorb some
of the neutrons and so control the chain reaction.)
( In atomic weapons, there are no control rods and so it is
an uncontrolled chain-reaction.)
Key-words:
Nucleus
Neutron
Absorb
Nuclei
Neutrons
Energy
Chain reaction
Fission
