HOW / WHY / EXPLAIN 2. FORCES AND MOTION Explain why a kick-boxer from Thailand fights without gloves will cause more injury to their opponent.

• When the boxer uses no gloves the time of impact is shorter.

• Impulsive force will be greater. • Cause more injury

Why does a supertanker needs to stop its engine over a distance of about 3 km before it can stop?

• Supertanker has a bigger mass • Bigger mass meant the supertanker has bigger inertia.

Explain how using of the safety belt can avoid the driver from serous injury. • Driver will thrown forward when the car

involved in accident. • By fastening the safety belt, the driver will not

thrown forward. • The seat belt will lengthen slightly, the

impulsive force acting to the driver will be less.

Explain why a player need to wear glove to catch a fast moving softball • Glove will lengthen the time of impact • Impulsive force will be reduce • Avoid injury to the player.

Explain how the forces between the molecules caused the elasticity when the spring is compressed or stretched • There are two type of forces • Attraction force and repulsive force between

the particles of the solid • When the solid is stretched, the molecules

displaced away from each other • Attractive forces are acting to oppose the

stretching • When the solid is compressed, the molecules

is displaced closer to each other. • Repulsive force are acting to oppose the

compression

3. FORCES AND PRESSURE Why it is easier to press thumbtack into a desk compare to the coin.

• Thumbtack has smaller area contact with the desk. With same pressure, smaller area will result of higher pressure.

Explain why a bulldozer uses broad tires.

• Broad tyres have bigger surface area contact with the ground.

• Bigger surface area will produces smaller pressure. • The bulldozer will not sink into the ground.

Why bigger tires is suitable to use when driving on the soft ground.

• Bigger tires have bigger contact area. • Pressure acting to the ground will decrease • Tires will not sink into the soft ground.

Explain why a ship may sink when it sails from sea water to fresh water?

• Fresh water is less dense sea water. • Buoyant force is smaller • The ship will start sink to displace more water in order to support the weight of the ship.

• If the buoyant force is less than the weight of the ship, the ship will sink.

Why is the cross-sectional area of the rear brake cylinder of the right wheel is the same as the cross-sectional are of the rear brake cylinder of the left wheel

• Equal force applied to the left and right wheel. • To avoid the car from skidding.

Explain the working principle of a siphon.

• Siphon works based on pressure difference. • PressureB > PressureA • The atmospheric pressure pushes the surface of the liquid.

• Causes the liquid flow into the tube.

Explain why a larger force is applied to the bigger front brake piston compare to the smaller rear brake piston.

• The surface area of the front brake piston is larger. • Force applied is directly proportional to the surface area. (F =PA)

How a submarine on the surface of the sea can submerge

• Water is sucked in the ballast tank. • Weight of submarine > buoyant force

Explain how the toothpaste flows out from the tube and name a physics principle related to it.

• Pressure is applied to the toothpaste tube • The toothpaste carry and apply the pressure of the equal magnitude to the whole tube.

• Pascal’s Principle

Explain how the air pressure difference occurs at the different side of airplane wing.

• The shape of cross section of the wing causes the speed of air flow above the wing to be higher.

• When the speed of air is higher, the pressure will be lower.

• Bernoulli’s principle.

Explain why the dam wall is thicker at the bottom. • Pressure in water increase with depth. • Pressure at the bottom is higher. • To withstand higher pressure

Explain why the ice block float in the water • Volume of water increased when freezing and

become ice. • Mass of the water is same but volume become

bigger • Density of the ice is smaller than water

Explain how submarine is able to submerge in the sea • Sea water is pumped in the ballast tank. • Weight of submarine > buoyant force.

Explain how submarine is able to float. • Sea water is pumped out from the ballast tank. • Weight of submarine < buoyant force.

Explain why the sinking of the same boat is different in the sea water and fresh water. • Sea water is denser • Boat displaced less sea water and gain the

same upthrust force. • Therefore boat sink less in the sea water

Why a hydraulic brake is less effective if air bubbles are present in the hydraulic fluid • Some of the force is used to compress the air

bubbles • Less force use to push bigger piston.

Explain why a hydraulic jack is also known as a force multiplier • When the small piston is pull out, the hydraulic

oil is drawn from the reservoir to the small piston.

• When the small piston is push down. The hydraulic oil will be compress.

• The pressure will transmit uniformly to the bigger piston.

• Force exerted to the bigger piston is also bigger.

• The force is multiplied.

Explain the purpose of Plimsol line • Plimsoll line is line mark on the body of the ship. • This is the mark where the ship may load with

maximum loads. • Make sure for the safety of the ship. • Plimsoll line has many level because different

water has different density eg cold/hot/fresh water/sea water.

Explain why ship can float in sea water. • Ship displaced out water. • Weight of water displaced = buoyant force. • Buoyant force = weight of ship. • Ship floats.

4. HEAT Why it is a good idea to reduce the pressure of the air in the tires before make a long journey.

• During the long journey the tires will be heated. • Pressure of the air will increase when the temperature increase.

• To avoid the tires burst.

Explain why water is normally used as a cooling agent in a car engine.

• Higher specific heat capacity. • Absorbed more heat but not easy to become hot • Cheaper • Higher boiling point. • Lower viscosity

Explain why a scald from steam is more serious than the one from boiling water

• Steam condenses to form water and release higher c latent heat of vaporization. Expose to steam mean expose to higher amount of heat.

How does sweating helps to cool down your body?

• Sweat absorbs heat from body to evaporate. • Body loss heat and become colder

Explain the formation of sea breeze • Land has lower specific heat capacity than the

sea water. • During day time land become hot faster and air

above the land also become hot and has low density.

• The air rise up and leave empty space on the surface of land.

• This empty space is filled with cold air from sea to form sea breeze.

Explain the formation of land breeze • Land has lower specific heat capacity than the

sea water. • During night time sea water become cold

slower (still hot) and air above the sea also still hot and has low density.

• The air rise up and leave empty space on the surface of the sea.

• This empty space is filled with cold air from land to form land breeze.

State characteristics of gas at absolute zero. • Volume = 0 • Pressure = 0 • Kinetic energy = 0 • Molecules at rest.

How clinical thermometer can measure the patient’s body temperature. • Thermometer is placed in the mouth of the

patient. • Heat is transferred from patient’s body to the

thermometer. • Thermal equilibrium between the thermometer

and patient’s body is reached. • Temperature of the thermometer = temperature

of the patient’s body.

By using kinetic theory, explain why there is no increase in temperature when ice is melting • Heat supplied is used to break up bonds

between molecules, • Heat is not used to increased the kinetic

energy

Why heat is removed from the forehead of a person • The temperature of forehead > temperature of

cooling pad. • More heat transferred from forehead to the

cooling pad. • Temperature of cooling pad increased while

temperature of forehead will decreased.

Explain how thermometer can be calibrated. • Put the thermometer in melting ice. Mark the

mercury level as 0oC • Put the thermometer in boiling water. Mark the

mercury level as 100oC. • Divide the length of the mercury between 0oC

and 100oC to 100 divisions. • Each division = 1oC

Using kinetic theory explain why pressure of gas change when the volume change. • When volume of the gas is decreased, the

molecule of the gas will collide more frequent will the wall of the container.

• More impulsive force will act to the wall with same surface area

• Pressure increase.

Why the temperature remain constant when water is boiling to become steam

• Heat absorbed is used to break bond between water molecules.

• Not used to increase the kinetic energy of the molecules.

• Temperature increase when kinetic energy increase.

Explain why gas pressure increase when temperature increase. • When temperature increase, kinetic energy of gas

molecules increase. • Rate of collision to the wall container also

increase. • Impulsive force exerted to the surface of wall

increase. • Pressure increase.

Why cooked fish steam is faster.

• Steam has higher specific latent heat of vaporization.

• When stem is condensed a lot of heat release. • Fish absorbed this heat and cook faster.

Explain the formation of land breeze

• Land has lower specific heat capacity than the sea water.

• During night time sea water become cold slower (still hot) and air above the sea also still hot and has low density.

• The air rise up and leave empty space on the surface of the sea.

• This empty space is filled with cold air from land to form land breeze.

Why gel in cooling pad is used to remove heat from patient. • Gel has higher specific heat capacity. • Gel is cool down in refrigerator. • Cool gel is applied to the forehead of patient. • Although gel absorbed more heat, the

temperature of the gel increases slowly. • The gel can be used for longer time.

5. LIGHT Explain why periscope using prisms produces clearer image.

• All lights is reflected • Through total internal reflection.

Explain why the image of the coin appears nearer to the surface of the water.

• Light travels from denser to less dense medium. • Refracted away from normal.

Explain why a fish in a pond able to see objects around although there are obstacles.

• Draw a diagram to show

• Because total internal reflection. • 1800 fish eye view

Describe how you estimate the focal length of a convex lens. • Convex lens is aimed at a distance object eg

tree. • Adjust screen until get a sharp image. • Parallel light from distance will be focused to a

point called focal point. • Measure distance between convex lens and

the screen as focal length

Explain the formation of mirage. • The layer of air nearer the road is warmer • The density of the air decrease nearer to the

road surface • The light travel from denser to less dense area. • The light refract away from the normal. • When the angle of incidence > critical angle,

total internal reflection occurs.

State 2 conditions under which the light ray would undergo total internal reflection. • Light travel from denser to less dense medium • Angle of incidence > critical angle

Explain the formation of mirage. • The air on the hot ground is hotter. It is less

dense. • The higher air is cooler. It is denser • Light from sky travel through denser to less

dense air. • Total internal reflection occurs when I > c

State the advantage of using fiber optic cable• Can carry large amount of data/transmission• Transmit signal with little loss of signal.• Can transmit a large amount of signal at one

time • Thinner and lighter.

Explain the formation of red sky during sunset.

• Light consists of 7 colors • λλλλ red is the longest • During sunset light traveling through thicker

atmosphere. • Only red can be seen

Explain how to built optical fiber for telecommunication

• Optical fiber consist of two layer of glass.• Inner core have higher refractive index from outer cladding.

• When light travel with i>c. • The light will experience total internal reflection.• Light come out from the other end.

Explain how to produced parallel light beam• Use concave mirror, and a bulb • Bulb is placed on the focal point of the concave

mirror. • Light from the bulb will be refracted parallelly.

6. WAVES Explain how the diffraction of sea wave occurs

• Wave pass through a slit/aperture or round a small obstacle

• Wave spread out

Explain why bright fringes and dark fringes are observed on the screen (Young’s double slit experiment)

• Constructive interference produces bright fringes.• Destructive interference produces dark fringes

Explain why echo sound occurs

• The sound is reflected by an object that is far enough from the observer.

• The time interval between the original sound and the reflected sound is larger.

• Both sound can be heard

Explain how the loudspeaker is able to produce sound waves

• Frequency audio is an ac current • The signal is sent to the coil • The coil will vibrate • Because the force acting on a current carrying conductor in a magnetic field.

• Cause the cone to vibrate. • The cone will vibrate the air molecules to produce sound.

optic cable Can carry large amount of data/transmission Transmit signal with little loss of signal.

of signal at one

Explain the formation of red sky during sunset.

During sunset light traveling through thicker

Optical fiber consist of two layer of glass. Inner core have higher refractive index from outer

The light will experience total internal reflection.

Explain how to produced parallel light beam

Bulb is placed on the focal point of the concave

Light from the bulb will be refracted parallelly.

Explain how the diffraction of sea wave occurs through a slit/aperture or round a small

Explain why bright fringes and dark fringes are observed on the screen (Young’s double slit

Constructive interference produces bright fringes. produces dark fringes

The sound is reflected by an object that is far

The time interval between the original sound and

loudspeaker is able to produce

Because the force acting on a current carrying

vibrate the air molecules to produce

Explain why the submarine used ultrasonic wave but not ordinary sound wave?

• Ultrasonic has higher frequency.• Has higher energy • Can travel further

Explain why a double-glazed glass is use for the observation tower at the airport• Glass vibrate at its own natural frequency• The airplane engine caused noise and vibrate

the air particle • Due to resonance the glass particle also

vibrate at maximum amplitude.• The glass must be double

stronger glass • To the window from break.

Explain why speed of sound is greater in the sea than in the air • Sound need medium to propagate.• The molecules of sea water is closer each other

compared to the air. • Sound is transferred easily.

Explain the formation of dark and bright fringe in the young’s double slit exp

• Light will experience interference.• Constructive interference will produce bright fringe.• Destructive interference will produce dark fringe.

Explain why sea wave follow the shape of the coast.• The wave travel from deeper to shallower region.• The wave reach shallower region at cape.• Wave is refracted towards normal and

concentrated to the cape. • Wave follow the shape of coast

Explain why a boy on the ground cannot hear his mother the 20Th floor shouting at him.• Air at 20th floor is cooler and denser,• Air above the ground is hotter and less dense.• Sound from mother travel from denser to less

dense medium • Sound will be refracted back to the • Hot heard by the boy

7. ELECTRICITY Explain why it is more dangerous to touch the live wire of a mains supply, rather than the neutral wire.

• Live wire has higher potential (230V)• Our bodies are at earth potential (0V)• If we touch the life wire, there will be a large potential difference between the live wire and our bodies.

• A large current will flow through our bodies.• The neutral wire stays at earth potential (0V).• If we touch the neutral wire, there is no potential difference across us and no current flows.

Why one bulb connected to 2 dry cell (dry cells connected in parallel each other) light up brighter then one bulb connect to one dry cell?• When two dry cells connected in parallel• The emf remains the same but the internal

resistance become smaller.• A larger current will flow through the bulb to

make it brighter.

Explain why the submarine used ultrasonic wave

Ultrasonic has higher frequency.

glazed glass is use for the tower at the airport

Glass vibrate at its own natural frequency The airplane engine caused noise and vibrate

Due to resonance the glass particle also vibrate at maximum amplitude.

-glazed or made from

To the window from break.

Explain why speed of sound is greater in the sea

Sound need medium to propagate. The molecules of sea water is closer each other

Explain the formation of dark and bright fringe in

Light will experience interference. Constructive interference will produce bright fringe. Destructive interference will produce dark fringe.

Explain why sea wave follow the shape of the coast. The wave travel from deeper to shallower region. The wave reach shallower region at cape. Wave is refracted towards normal and

Wave follow the shape of coast

boy on the ground cannot hear his floor shouting at him.

floor is cooler and denser, Air above the ground is hotter and less dense. Sound from mother travel from denser to less

Sound will be refracted back to the air.

Explain why it is more dangerous to touch the live wire of a mains supply, rather than the neutral wire. Live wire has higher potential (230V) Our bodies are at earth potential (0V)

there will be a large potential difference between the live wire and our

A large current will flow through our bodies. The neutral wire stays at earth potential (0V). If we touch the neutral wire, there is no potential

urrent flows.

Why one bulb connected to 2 dry cell (dry cells connected in parallel each other) light up brighter then one bulb connect to one dry cell?

When two dry cells connected in parallel The emf remains the same but the internal

smaller. A larger current will flow through the bulb to

Function of resistor • To limit/fix amount of current in circuit.

Explain why parallel circuit is used in the house lighting circuit. • All appliances will get same voltage. • The appliances can be on and off separately. • If one appliances is blow out, the other can still

be use

Why car cannot be started using 8 dry cells, 1.5V each. Although the total of voltage is 12V. • Each cell has internal resistance. • When the batteries are connected in series (to

get 12V) the internal resistance became higher. • The amount of current became smaller. • The starter cannot be operated.

8. ELECTROMAGNETISM Why a solar cooker is environmental friendly?

• No pollution • Renewable source of energy

Explain the working principle of an electric bell.

• Current flow in the coil. • Soft iron core is magnetized. • Attract/pull the hammer. • Hammer hit the gong • The contact is open and no current flow. • Soft iron core loses its magnetism. • Spring will pull the gong back to its original position and contact is closed again. Explain why the core of the transformer is made from soft iron.

• Can be magnetized and demagnetized easily. • Reduce loss of power

Explain the working principle of transformer

• Ac current flow in the primary coil. • Primary coil will have the alternate magnetic fluxs. • The iron core will link the alternate magnetic fluxs to the secondary coil.

• The will be magnetic fluxs cutting in the secondary coil.

• Emf/current will induced in the secondary coil. List the factors that cause the energy loss in a transformer.

• Production of eddy current. • Resistance of the coil will result the heating effect. • Magnetization and demagnetization of the iron core. • Magnetic fluxs leakage

Explain method to increase the deflection of the compass pointer near the solenoid.

• Increase the number of turns of the solenoid. • Increase the current in solenoid/use more batteries • Reduce the resistance of the wire • Use larger diameter of the wire. • Bring the compass nearer to the solenoid

How dc current is produced by the dc generator. • Rotate the coil in clock wise direction • The coil cut across the magnetic field. • Current is induced in the coil. • The commutator change the direction of the

current in the coil so that the direction of current in external circuit always the same.- dc

Explain how the dc motor is able to rotate • When the current flow into the coil, magnetic

field is produced. • And forces are produced. • Catapult field is produced. • The forces are in opposite direction. • This pair of forces produce the turning effect

on the coil

Explain what is catapult field. • Magnetic field is produced around a current

carrying conductor. • This current carrying conductor is place in the

magnetic field of the magnet bar, • The resultant of magnetic field produced by the

current carrying conductor and magnetic field by the magnet bar to form catapult field.

Explain the working principle of the transformer/ • When ac voltage is supplied to primary coil, ac

will flow. • The soft iron core is magnetized • The magnet produced varies in magnitude and

direction. • This causes the changing magnetic flux pass

through the secondary coil. • An induced emf across the secondary coil is

produced

Explain function of electromagnetic relay

• Use as an automatic switch to switch on the second circuit.

• When current flow, relay will be an electromagnet. • Attract the iron armature • Second circuit will be on.

Explain the working principle of the transformer/

• When ac voltage is supplied to primary coil, ac will flow.

• The soft iron core is magnetized • The magnet produced varies in magnitude and

direction. • This causes the changing magnetic flux pass

through the secondary coil. • An induced emf across the secondary coil is

produced

Explain the working principle of a moving coil galvanometer • When current flow through the wire coils,

magnetic field is produced. • This magnetic field interacts with magnetic field

of permanent magnet. • Producing a pair of forces that turn the coil

together with the pointer. • The spring return the coil to its original position

when the current is cut off. • The bigger the current, the bigger the force, the

bigger the deflection of pointer.

State the factors that increase the amount of induced current • Increase number of turn of coil • Increase the strength of magnetic field. • Increase the diameter of the wire of solenoid. • Increase the relative speed of magnet

Why dc current is use to make electromagnet • Dc is constant current. • Flow in one direction. • Produced magnetic field that is not changing the

direction.

Explain how a circuit breaker works. • When too high current flow, magnetic field

strength become stronger • Electromagnet is able to pull the iron armature • It will release the catch, contact separate and

current does not flow. • When reset button is pressed, spring Q pulls the

soft iron armature back to its original position

9. ELECTRONICS Why there is a current flow when diode is forward biased when connected in the circuit?

• Electron in the diode will attract to the +ve terminal and hole will attract to the –ve terminal.

• Depletion layer will be narrower. • Resistance of the diode will be smaller. • Large current can flow through the diode.

Explain how the p-type of semiconductor is produced. • Si is doped with element from group III. • Group three has only 3 electron valens. • One extra positive hole will no be occupied

with the electron. • Hole will be the majority charge carrier and

called as p-type semiconductor

Explain how transistor is used as an automatic switch to control the night lamp.

• When it is dark resistance of the LDR higher. • Voltage across the LDR is higher (base circuit) • Higher Ib flow. • Higher Ic flow. • Lamp is light on

Explain how n-type semiconductor is produced. • Pure semiconductor e.g Silicon doped with

element from group V. • Eg. Phosphorous. • Phosphorous have 5 electrovalens. • When doped, new substance have extra one free

electron. • N-type semiconductor has free electron as a

majority charge carrier

10. RADIOACTIVITY Why the tracks of beta particles produced in a cloud chamber is thin and not straight?

• Beta particles have medium ionization • Beta particles have smaller mass. • The direction of the particles change when collide with the air molecules.

Explain how the radioactive rays is detected by the GM Tube. • The radioactive emission enters the tube

through the mica windows • And ionizes the krypton gas • The electron and the positive ions are attracted

towards anode and cathode respectively and produces pulses of current.

Explain ho to study the intake of fertilizer by plants. • The fertilizer that contains a radioisotope is

injected into the plant. • Wait for a few days for the fertilizer to be

absorbed. • Use GM tube and rate meter to detect the

radiation • The location of where the fertilizer has gone to

are located and analyzed Explain how Carbon-14 can be used to estimate the age of a dead plant which contain carbon • Carbon-14 is a radioactive substance which is

easily absorbed by living plants • After the plants die, the activity of the Carbon-

14 will decline since no new Carbon-14 is absorbed

• By knowing the half life of Carbon-14 and calculating the activity of Carbon-14, the age of the plant can be determine.

How nuclear fusion can produce energy • Nuclear fusion is the process of combining

two lighter nuclei to form a heavy nucleus • After the combining process there will be a

mass defect. • The mass defect is converted to energy using

this formula. E = mc2 Explain how Sr-90 is used to measure the thickness of paper in a paper industry • Put the radioactive source opposite the

detector • Detector is connected to the thickness

indicator • Detector detect the reading of the changes in

count • Thickness is measured with the thickness

indicator • If the reading of the detector is less than the

specified value, the thickness of paper is too thick

Describe how to the radioisotope get into patient body and how doctor diagnosis his disease

• Radioisotope is injected into the blood stream. • Detector is used to detect radiation from the body. • The area that has high radiation show it might has health problem Explain the arrangement of the paper thickness detector apparatus and state how it is used to detect the thickness of the paper

• Detector is put opposite to the radioactive source. • Detector is connected to the counter. • If the reading is too low from the standard reading

the paper is to thick. • Signal send to roller to decrease the gap between

rollers. • If the reading is too high, the paper is to thin. • Signal send to the roller to increase the gap

between rollers.

Why technetium 99 is suitable to be used in medical diagnosis, to detect defects in bone, kidney, heart and organ? • Half life is 6 hours. Not active in body for longer

time. • Produce low energy of gamma ray. Less

dangerous.