Paper 2 Definitions

Question 1

Define capacitance.

Answer 1

The amount of charge an object can store per unit
potential difference across it.

Question 2

Describe the construction of a capacitor.

Answer 2

Parallel plates separated by a dielectric.

Question 3

What is the area under a p.d/Q graph?

Answer 3

Electric potential energy stored.

Question 4

What does the time constant represent?

Answer 4

The time taken for the charge on a discharging capacitor to fall to about 37 %
of Q0. Or the time taken for the charge of a chaging capacitor to rise to about
63 % of Q0.

Question 5

What do the charging I/t, V/t and Q/t graphs look like?

Answer 5

Exponential decay, curve up to max, curve up to max

Question 6

What do the discharging I/t, V/t and Q/t graphs look like?

Answer 6

All exponential decay

Question 7

How can you calculate the radius of curvature?

Answer 7

F = mv^2 / r and F = BQv

Question 8

How can you calculate the frequency of rotation?

Answer 8

f = v / 2(pi)r and r = BQ / 2(pi)m

Question 9

How do cyclotrons work?

Answer 9

1. Charged particles fired into electrode
2. Magnetic field makes them follow a semi-circular path
3. Applied p.d. between electrodes accelerates particles across the gap into the
   next semi-circle
4. Speed of particle now higher – so follows a path with a slightly bigger radius
5. When it gets to next gap, p.d. has reversed so it is accelerated again –

speed goes up – radius gets even bigger

6. particle spirals outwards getting faster

Question 10

Faraday’s law?

Answer 10

The magnitude of induced e.m.f. is directly
proportional to the rate of change of flux
linkage.

Question 11

Lenz’s law?

Answer 11

The induced e.m.f. is always in the direction such
as to oppose the change that caused it.

Question 12

How do transformers work?

Answer 12

1. a.c. Current passes into primary coil – makes a magnetic field
2. Magnetic field of coil magnetises iron core (induced magnetism)
3. Magnetic field in iron core is alternating – because current in coil is a.c.
4. Alternating B field in the iron core makes an alternating p.d. in second coil
   (generator effect)
5. Get a.c. out of the second coil

Question 13

How do transformers lose energy?

Answer 13

The iron core being continuously cut by flux causes currents in the core,
called eddy currents

Eddy currents dissipate energy as heat

Heat is also generated from resistance in the coils

Energy is also needed to magnetise and demagnetise the core which is wasted

Question 14

Define force field.

Answer 14

A region in which a body experiences a
non-contact force.

Question 15

Define gravitational potential.

Answer 15

Work done in moving a unit mass from infinity to
the point.

Question 16

How to derive T^2 is proportional to r^3?

Answer 16

F = mv^2 / r = GMm / r^2

Question 17

Define escape velocity.

Answer 17

The minimum speed an unpowered object needs
to leave the surface of a planet in order to leave its
gravitational field.

Question 18

How to calculate escape velocity?

Answer 18

KE lost = GPE gained

Question 19

What is the equation for escape velocity?

Answer 19

ve = root of 2GM / R

Question 20

Define electrical potential.

Answer 20

Work done in moving a unit positive charge from
infinity to the point.

Question 21

Define binding energy.

Answer 21

The energy needed to give the nucleus to completely separate all the nucleons.

Question 22

How does the moderator slow neutrons down?

Answer 22

n lose KE by elastic collisions with the moderator.

Question 23

Define internal energy.

Answer 23

The sum of the randomly distributed kinetic and potential energies of the particles in that substance.

Question 24

Define specific heat capacity.

Answer 24

The amount of energy needed to increase the temperature of 1kg of a substance by 1 degree Celsius.

Question 25

Define specific latent heat.

Answer 25

The quantity of thermal energy needed to be gained or lost to change the state of 1kg of a substance.

Question 26

What is Boyle’s law?

Answer 26

At a constant temp and fixed mass the pressure and volume of a gas are inversely proportional.

Question 27

What is Charles’ law?

Answer 27

At a constant pressure and fixed mass the volume of a gas is directly proportional to its absolute temperature.

Question 28

What is Gay-Lussac’s law?

Answer 28

At a constant volume and a fixed mass the pressure of a gas is directly proportional to its absolute temperature.

Question 29

What are 5 assumptions of kinetic theory?

Answer 29

1. All particles are identical
2. particles move at random
3. all collisions are perfectly elastic
4. particles move in straight lines between collisions
5. gas has a large number of particles

Question 30

Give the steps to deriving the kinetic theory equation.

Answer 30

1. Determine the change in momentum as a single molecule hits a wall perpendicularly
2. Calculate the number of collisions per second by the molecule on a wall
3. Calculate the force exerted by the molecule on the wall
4. Calculate the total pressure for one molecule
5. Consider the effect of N molecules moving randomly in 3D space
6. Consider the speed of the molecules as an average speed
7. Consider the volume of the box

Question 31

What is the triple point of water?

Answer 31

273K, the temperature at which pure water exists in thermal equilibrium with ice and water vapour.

Question 32

What is the latent heat of fusion?

Answer 32

Melting or freezing.

Question 33

What is the latent heat of vapourisation?

Answer 33

Boiling or condensing.

Question 34

What is Brownian motion?

Answer 34

Pollen grains on water move randomly, resulting from collisions with the fast, randomly moving particles in the water.