Physics Past Paper Corrections

Question 1

Define elastic behavior

Answer 1

Returns to original length or shape once force is removed.

Question 2

Advantage of 24h orbit satellite

Answer 2

The satellite is always about the same point on the Earth (Geostationary Object).

Question 3

Charger moved into shade & output power decreases

Answer 3

Longer chagrin time needed because there is lower current. P = IV

Question 4

Sources of background radiation

Answer 4

Cosmic radiation, nuclear waste, sources from medical sources, radon gas, some foods like bananas

Question 5

Effect of beta emission on nucleus

Answer 5

The neutron number decreases by 1 as it changes into a proton, so the atomic number increases by 1.

Question 6

Why do bubbles expand as they rise towards the surface?

Answer 6

Pressure decreases as depth decreases, since P = hρg. Additional bubbles join together as they rise.

Question 7

Damage of infrared

Answer 7

Skin burns.

Question 8

Damage of ultraviolet

Answer 8

Damage to surface cells & blindness.

Question 9

Why do planets close to the sun take less time to orbit?

Answer 9

They have a smaller orbital path.

Question 10

Convection current explanation

Answer 10

Air becomes hot. Air expands & becomes less dense, hence it rises.

Question 11

How can a turbine generate electricity?

Answer 11

Hot air turns turbines, and turbines turn the generator.

Question 12

KE formula

Answer 12

½ mv^2

Question 13

What star colour is coolest?

Answer 13

Red

Question 14

What is reaction force?

Answer 14

The second object exerts an equal and opposite force on the first.

Question 15

Use of gamma rays

Answer 15

Used to sterilise medical tools because gamma kills bacteria.

Question 16

Use of X-rays

Answer 16

Used to photograph bones because x-rays can penetrate soft tissues but not bones.

Question 17

Use of ultraviolet

Answer 17

Used for detecting security ink because it fluoresces with ultraviolet lighting

Question 18

Use of infrared

Answer 18

Used for optical fibre communication because they can undergo total internal reflection

Question 19

Use of microwaves

Answer 19

Used for satellite communication because microwaves can penetrate earth’s atmosphere.

Question 20

Use of radio waves

Answer 20

Used for long-range communications because they can be reflected from the Earth’s atmosphere.

Question 21

Describe how the average kinetic energy of the gas particles changes when the temperature of the gas increases.

Answer 21

Average kinetic energy increases in direct proportion to kelvin temperature.

Question 22

Describe doppler effect (object moving away)

Answer 22

Frequency decreases and wavelength increases because wave speed is constant.

Question 23

Why does fusion need high temperatures?

Answer 23

Hydrogen nuclei repel, so they need a high kinetic energy to get close enough to fuse together.

Question 24

Define ionisation

Answer 24

Removal of electrons from an atom

Question 25

Why does alpha not reach workers?

Answer 25

Alpha particles are absorbed by a few cm in air so alphas cannot reach workers.

Question 26

Why do balloons expand when pressure outside decreases?

Answer 26

The pressure outside balloon is lower than inside balloon, and this pressure difference causes a force which is outwards on ballon & causes extension of balloon.

Question 27

How to increase the magnitude of magnetic force (magnet)?

Answer 27

Increase the magnetic field strength by using stronger magnets

Question 28

How to increase the magnitude of magnetic force (current)?

Answer 28

Increase the current by increasing the voltage of the power supply.

Question 29

How to make the circuit vibrate?

Answer 29

Using alternating current since it have changing current direction

Question 30

Magnets difficult to magnetise

Answer 30

Hard magnetic materials

Question 31

Risk of radioactive tracer (gamma) to doctors & patients

Answer 31

Patients will have procedure rarely so risk is low, whereas doctors will perform procedure regularly so risk is higher

Question 32

Why gamma (short half life) good as medical tracer

Answer 32

Gamma can be detected outside body & activity will fall to safe level quickly

Question 33

Why does coil heat up when there is current in it?

Answer 33

Coil has resistance & electrons lose energy due to electron collisions with lattice ions in the coil.

Question 34

Why does black colour get hot?

Answer 34

Black is a good absorber of radiation

Question 35

How is the main sequence formed from nebula?

Answer 35

Nebula is a cloud of dust & gas which collapses due to gravity. The temperature of the cloud increases creating a protostar.

Question 36

How does the main sequence become red giant?

Answer 36

Hydrogen fusion stops & core collapses and temperature increases. Star expands to become red giant & surface temperature decreases.

Question 37

How does red giant become white dwarf?

Answer 37

Helium fusion begins & white dwarf formed when helium fusion stops in core.

Question 38

How to vary current?

Answer 38

Change the number of cells or use variable power supply

Question 39

What colour reduces rate of energy transfer?

Answer 39

White because it is a poor emitter of infrared.

Question 40

Hooke’s Law On Graph

Answer 40

Force and extension are directly proportional. Line is straight & passes through origin.

Question 41

Fusion over fission (safety)

Answer 41

No long term storage problems & no shielding required

Question 42

Why is variable resistor used?

Answer 42

Allows the current or voltage to be varied

Question 43

What does colour of star depend on

Answer 43

Surface temperature

Question 44

Which part of nuclear fission reactor reduces risk of neutrons?

Answer 44

Lead shielding absorbs high energy neutrons.

Question 45

Contamination

Answer 45

When a non-radiactive object comes into contact with a radioactive material.

Question 46

Irradiation

Answer 46

The exposure of an object to radiation.

Question 47

Fusion definition

Answer 47

Creation of a large nucleus from small nuclei resulting in a loss of mass & the release of energy.

Question 48

Why does plastic cover on pool reduce heat loss?

Answer 48

Plastic cover is good insulator that traps air which is also a good insulator. Conduction & convection reduced & less evaporation.

Question 49

What happens to wavelength of light when it goes from air into water?

Answer 49

Wavelength decreases because wave speed decreases & frequency remains constant.

Question 50

Why is gamma used for wooden box?

Answer 50

Gamma is more penetrating than alpha, therefore gamma can pas through box.

Question 51

Extension after LOP

Answer 51

Above original, straight & not return to origin

Question 52

How is star formed in nebula?

Answer 52

Gas collapses, the temperature of the gas increases & fusion starts.

Question 53

Fusion in star

Answer 53

Two small nuclei join tgether to produce a large nucleus releasing energy.

Question 54

Why does toaster have parallel?

Answer 54

Wires have a higher voltage

Question 55

Accurate use of measuring cylinder

Answer 55

Placed on horizolntal surface & ensure it is empty before use.

Question 56

How does motion of molecules increase with temperature?

Answer 56

Mean kinetic energy increases.

Question 57

Properties of all waves

Answer 57

All waves reflect, refract, transfer energy & have wavelength

Question 58

What happens if light hits boundary at 90 degrees?

Answer 58

Angle of incidence is zero, so abgle of refraction must also be zero.

Question 59

How does generator produce voltage?

Answer 59

Turning handle makes coil rotate and the coil cuts through magnetic field of permanent magnets.

Question 60

Why no Doppler effect beween Earth & satellite?

Answer 60

No relative motion between point on Earth's surface and satellite, so no frequency change.