Physics Mistakes Paper 2 mistakes (loads of them)

Question 1

Answer 1

Question 2

In nuclear fusion, two positively charged nuclei must overcome the effects of the repulsive electrostatic force between them.
Explain the two conditions needed to overcome the effects of this repulsive force and achieve nuclear fusion.

Answer 2

Question 3

A bag of ice is placed on the lower leg, vertically above the centre of gravity.
This causes force X and force Y to increase.
The bag is then moved towards the person’s foot.
Describe how force X and force Y change as the bag is moved towards the person’s foot.

Answer 3

• force X decreases;
• force Y increases;
• change by the same amount;
• total force remains the same;

Question 4

Give two reasons why the energy from the heater is not all retained in the thermal store of the water.

Answer 4

• heating of beaker/heating of thermometer; allow idea of ‘heat
  goes to beaker/thermometer’
• heating of surroundings/heating of insulation; allow idea of ‘heat
  going to surroundings or insulaton’
• insulation not perfect; e.g. insulation conducts or radiates
• hole(s) in lid for thermometer/heater leave gaps

Question 5

Explain how a transformer works. Include reasons for using:
- two coils
- the iron core
- an a.c. power supply

Answer 5

Question 6

State how the primary coil of the transformer can be changed to increase the output voltage

Answer 6

less turns (on the primary coil)

Question 7

Explain whether or not the energy in the kinetic store of the particles changes when the sample is changing state.

Answer 7

kinetic energy stays constant + any two from:
* temperature stays constant (during state change);
* (average) speed of particles does not change;
* (kelvin) temperature is (directly) proportional to (average) kinetic energy of particles;

Question 8

State the principle of conservation of momentum.

Answer 8

idea that (total) momentum before = (total)
momentum after (event);

Question 9

Answer 9

Question 10

Give the name of the piece of equipment that is connected to the oscilloscope to detect the sound wave.

Answer 10

microphone

Question 11

What is the equation for frequency?

Answer 11

Frequency = 1 / time period

Question 12

Answer 12

B – 16 g

Question 14

The chocolate is heated at a constant rate until the temperature reaches 45°C.
The chocolate has a melting point of 32°C and a boiling point of 55°C.
(i) Describe the motion of the particles in the chocolate when the chocolate is at a temperature of 45°C.

Answer 14

(movement now) random;
idea that particles are no longer in fixed
position;

Question 15

Answer 15

• (uranium) initial nucleus absorbs a neutron
• (uranium) nucleus splits/fission releasing (further)
  neutron(s);
• idea of neutrons can be absorbed by or can cause
  further fissions with other (uranium) nuclei

Question 16

Give a reason why the nuclear process in stars does not happen at low temperatures and pressures.

Answer 16

idea of (electrostatic) repulsion of nuclei or protons
(prevents fusion);

Question 17

Solar panels provide direct current to a device that outputs an alternating current so that the energy from the solar panels can be supplied to the National Grid.
(i) Explain why a step-up transformer is used to supply the National Grid

Answer 17

• (stepping up voltage) reduces current;
• reducing current reduces heating in the wire;

Question 18

Solar panels produce constant direct current (d.c.).
Explain why a transformer will not work when connected to constant direct current.

Answer 18

• constant current gives constant magnetic field;
• induction (in transformers) requires a changing
  magnetic field;
• no voltage will be induced;

Question 19

Light from galaxy B has twice the redshift as light from galaxy A.
Galaxy B is twice as far away from Earth as galaxy A.
Explain how these observations support the Big Bang theory of the origin of the Universe.

Answer 19

• link between twice the redshift and twice the speed;

PLUS one from:
- link between larger speed and larger distance;
- (which in turn means that) galaxies are moving apart
/moving away from each other;

Question 20

Explain the advantage of the concrete having a high specific heat capacity when it is used to heat water in the heating system.

Answer 20

• concrete can store/absorb/release a lot of energy
  (because of high SHC);
• water temp maintained for longer

Question 21

Natural gas can be burned to generate electricity.
Name the energy store that decreases when natural gas is burned.

Answer 21

chemical (energy store);

Question 22

Burning natural gas and the movement of water waves can both be used to generate electricity.
Discuss the advantages and disadvantages of these two methods of
generating electricity.

Answer 22

Question 23

Answer 23

MP1. idea that plastic is an insulator OR that metal
is a conductor;
MP2. idea that charge/electrons are transferred (by rubbing/friction);
MP3. charge/electrons remain/build up on plastic
parts (MUST MAKE CLEAR IT’S PLASTIC!)
MP4. charge/electrons flow through the metal parts/travel to earth;

Question 24

The sponge pad is held near a metal post that is connected to the ground.
The sponge pad discharges with a small spark through the air to the metal post.
The small spark between the sponge pad and the metal post demonstrates that the sponge pad is charged.
Describe a different experiment that could demonstrate that the sponge pad is charged.
You may draw a diagram to support your answer.

Answer 24

• idea of bringing pad near another uncharged
  insulator;
• attraction used to demonstrate charge on sponge;

Question 25

The car being tested is fitted with airbags. Using ideas about momentum, explain how an airbag reduces the force experienced by the dummy in the collision.

Answer 25

- idea that airbag increases the (collision) time; - reduces the rate of change of momentum;

Question 26

State what is meant by the term specific heat capacity.

Answer 26

- energy required - for a unit mass

Question 27

Answer 27

- idea that there must be a current in the wire - this current must be to the right;

Question 28

Answer 28

MP1. idea of avoiding fall objects from hitting hands/feet etc; MP2. taking care of heating effect of current; MP3. idea of protecting floor from damage;

Question 29

Explain how a main sequence star evolves into a supernova.

Answer 29

MP1. (hydrogen) fusion stops (in core) MP2. core collapses; MP3. (which) restarts fusion (in core); MP4. star becomes red supergiant; MP5. fusion of heavier elements stops (in core); MP6. star explodes (as supernova);

Question 30

The astronomers investigated supernovas that showed a red-shift in the wavelengths detected in different galaxies. The astronomers discovered that the red-shifted light detected from supernovas in nearby galaxies had shorter wavelengths than the red-shifted light detected from supernovas in galaxies further away. Explain how this discovery supports the Big Bang theory.

Answer 30

MP1. nearby galaxies show smaller {red-shift / change in wavelength}; MP2. nearby galaxies are travelling slower than further galaxies; MP3. (all light red-shifted) suggests universe is expanding; MP4. suggesting universe was once at a single point;