Physics

Energy

Energy units: Joule (J) or KwH= 1000W x 60 x 60 = 3.6MJ Units of energy, used for large amounts of energy e.g.: power stations

Motion (Kinetic) :

Wind Water – tidal

- Rivers (dams – hydroelectric 3 gorge dam/ Yangster Dam)

Chemical energy:

Batteries Food Fossil fuels/ fuels – paper, word, plastics

Heat energy

Light energy

Sound energy

Food is measured in calories

Power

Power = energy = J/S or Js-1 or W time

Energy = Power x Time = J or KwH

To change KwH into J you have to x 3,600,000 and to change J to KwH you have to ÷ 3,600,000

Calculation

A) Find the total amount of energy in KwH and in J which a 40W incandescent light bulb uses if it is switched on for 5 hours a day for 1 week.

Power = 40WTime = 5hrs x 7 days

Energy = power x time= 40 x 35= 1400 WH=1.4KwH

OR

Physics

=40 [5 x 60 x 60 x 7] = 40 x 126,000 = 504,000 J

B) Do the same for a low energy 7W bulb.

Power = 7W Time = 5hrs x 7 days

Energy = power x time= 7 x 35= 245 WH= 0.245 KwH

OR

= 7 x [5 x 60 x 60 x 7]= 7 x 126,000= 882,000J

Forms of energy

First law of Thermodynamics: energy cannot be created nor destroyed but it can be converted from one form to another. BUT there are always energy losses, when energy is converted from one form to another.

If I have a filament bulb which is equivalent to 40W only 2W are transferred into light. The other 38W are “lost” as heat. Energy lost=energy not useful

Stored Energy

1. Chemical energy stored in food (carbohydrates and fats), fossil fuels (oil, coal, petrol etc,) 2. Potential energy stored by an object when it is in a particular position as in gravitational

potential energy.

PE = m.g.h where m=mass –Units : Kg g (acceleration due to gravity) = 10ms-2

h = height – Units : m

e.g. Find the PE which a river has before falling a height of 50m. Flow of river = 250 Kgs -1 250 Kg of water flowing per second. It is impossible to find the total mass of water or air flowing. So mass flow per second is given.

PE = MGH = 250*10*50 = 125000 J

Nuclear energy is that energy stored inside the nuclei of atoms and is released after nuclei of heavy atoms are bombarded with neutrons. This does not cause air pollution like fossil fuels but nuclear radioactive waste is dangerous.

Physics

Kinetic Energy

This is that energy due to the motion of an object.

KE = ½ m x v2 where m = mass/Units : Kg; v= velocity / Units : ms-1

N.B Mass of water or air flowing is always given per second

Such energy sources are: Moving water – Hydroelectric dams, Moving air – Wind turbines where both are renewable sources of energy.

Find the energy a flowing river has if it flows at a rate of 30ms-1, and the mass flowing per second is 750 Kg

½ x 750 x 900 = 337500 J/S

Heat / Thermal Energy

Sometimes the equation below may be used to find the amount of heat required to raise the temperature of a material by ДT

Q (Heat Energy) = mx c x ДT ( Or ДѲ)

Where Q = quantify of heat supplied to material (= water is used). Units J m = mass of material Units KG c = Specific heat capacity = 4200 J/KgK Units J/ KG K ДT = change in temperature Units K= Kelvin

To measure temperature

Fahrenheit o FoCelcius is based on the properties 0oC Solid -> Water

100oC Liquid -> GasKelvin = Absolute scale temperature ( like oC)

C= Specific Heat Capacity of a substance= the quantity of heat required to raise the temperature of one Kg of it by 1K. The material in question is WATER since it is the most common liquid used for heating. Mass is included.

Heat Capacity = (mass is NOT included) Unit = J/K = joule per Kelvin

Solar Energy

The sun emits energy at a constant rate.

The solar constant (= insolation) describes the power falling on 1m2 of the Earth’s surface, at right angles to the Sun’s rays (= at equator). The value is Constant – because the sun always gives constant amount of energy = 1375 Wm2 = W/m2 (given) .(Dust particles (natural: Sand storms, volcanic dust) (Anthropogenic: man-caused: quarrying, buildings) and clouds reduce the sunlight reaching earth).

Physics

Obtaining solar energy:

Passive solar heating (no expenses to obtain energy)

Active solar heating

Solar energy falling on building and heating up the building.

Solar energy that is captured and converted into other forms of energy.

Adding insulation Solar water heaters: solar energy is used to heat up the water

South facing rooms are warmer Photovoltaic (PV) panels: solar energy is converted into electricity.

Electromagnetic radiation

This radiation can travel through a vacuum Te speed of this radiation in a vacuum is 3 x 108 ms-1 There is a whole spectral range of types of electromagnetic radiation The speed of this radiation can be found by: v = f x λ where velocity = speed (ms-1) , f =

frequency (s-1 or Herz) , λ = wavelength (m) The energy of this electromagnetic radiation can be found by:

E = h x f Where E = energy (J) H = Plank’s constant = 6.6 x 10-34 Js (given) F = frequency (s-1) or Herz or Hz

Thus, those electromagnetic waves with the highest frequencies have the highest energy. These include gamma, X rays, UV rays. Since they have the highest energies, they are also the most dangerous.

Energy efficiency

The second Law of Thermodynamics states that there is always inefficiency when heat from a heat engine is converted to mechanical work – a machine can never be 100% efficient since energy would be ‘lost’ as sound, friction etc. ‘lost’ implies the energy is changed into other USELESS FORMS of energy.

Efficiency given as percentage or decimal e.g. 50% or 0.4

Physics

5A) 1x105 =10000kgPE (height) = KE motion

B) PE = Power x Time T

C) PE = MGH 10 5 x 10 x 25 = 25 x 106 J/s or 25 x 106 W T 1 sec 1 sec

D) Loss of biodiversity due to changes in ecosystems floods, leading to displacement of people.

energyPEg97

2A) Kinetic Energy

B) Kinetic Energy of the water is converted to Kinetic Energy of the turbines as water flows and moves these turbines. These turbines then generate electricity.

KE of water -> KE of turbines -> Electricity

C) 1m3 of water has a mass of 1000 Kg 60m3 “ “ 60 x 1000 = 60,000 Kg

OR Density = mass = 1000 x 60 = 60, 000 Kg

Volume

D) KE = ½ x m x v2

= ½ x 60,000 x 52 = 750 000 J/S = 750 000 W = 750 KW

energyHEAT00

Physics

10 A) I) 20 x (2.8x 106) = 56 x 106 J

II) 10 x 106 J would raise the temperature by 1 Kelvin 56 x 10 6 56 x 106 would raise the temperature by 5.6 oC 10 x 106

III) No electricity required to heat the house. It is just heated by the sun.

B)I) carpets , curtains

II) Double Glazing

Energy HEAT04

2)A)I) Q = m x c x ДѲ m = 50 KG (50 L) Д = 60oC – 10oC = 50oC = 50 x 50 x 4200 = 10500000 J

II) 0.5 kwH energy per cycle1KwH = 3600000 J0.5 KwH = 1800000 J Total = 12300000 J

B) Q = m x c x ДѲ 100 x 4200 x 33 = 13860000 J

C) The temperature change remains the same.

D)I) Costs

Electricity, high temperature Cost of Dishwasher to manufacture it (to get raw materials) Repairs of dishwasher

D)I) Benefits

Less water than by hand Less energy used to wash the dishes

D)II) Costs

More water More energy

D)II) Benefits

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Lower temperature to heat water No appliance therefore no maintenance cost.

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EnergyHeat04secB

2)A)I) To absorb more heat II) To trap more heat energy (greenhouse effect) as infrared rays do not pass through the glass.

B) Adv- NO air pollution because it is using solar renewable energy. Electricity is produced from burning oil which causes air pollution. Dis- If there is clouds or dust, it does not work efficiently. - not accessible to everyone (no roof space or sunlight)

C) To transfer heat from the panel to the water

D) on 1m2 -> 1370 Watts of solar Energy for every 1m2 only 50% of 1370W becomes electricity 1370 = 658W or Electricity per m2

2685 W of electricity -> 1m2 of panel750 W of electricity -> ? 750 = 1.095 m2 685

E) Energy = m x c x ДѲ Power = 750 W Time = 10 hours = 27,000,000 s By subject of the formula Energy = P x T = 750 x 27,000,000 = 20,250,000,000 = 27,000,000 = m 105,000 = 257.14 Kg =M

Energyefficiency97

4)A) 1=boiler 2=turbine 3=condenser

B) stored chemical energy (fossil fuel) Heat energy (steam) Kinetic energy of turbines Electrical energy

C) Heat energy per 1Kgof coal = 25MJ 40% efficient Power output (electricity) 1000 MW Mass of coal in needed in 1 hr ?

Physics

Heat energy -> Electricity per 1kg25Mh -> 40% x 25 MJ = 10 MJ of electricity for every 1kg of coal burntPower output x 1hr (time) = Electrical energy delivered by the power station in 1 hr. 1000 MW x 60 x 60 = 3,600,000 MJ 1 Kg of coal provides 10 MJ of electricity? Of coal produces 3,600,000 MJ of electricity= 3,600,000 = 360,000 kg = 360 tons of coal required 10

Energyefficiency02

1)A) I) energyB) burning coalC) 1 KW of electricity is produced from 8 x 106 J of heat 1.2 x 107 x 8 x 106

= 9.6 x 1013 Joules of heat in one dayD) 1 kg of coal gives 107 J of heat ? kg of coal give 9.6 x 1013 J of heat? 9.6 x 10 13 = 6.6 x 106 kg of coal 1 x 107

E) IV - efficiencyF) Coal and oil contains sulphur as a natural impurity. This sulphur burns when these fossil fuels are burnt and these produce acidic gases called sulphur oxides which from ACID RAID.