Post Past Paper 2

Question 1

Why is an alternating EMF induced in a search coil when an alternating current is supplied to a larger coil surrounding it?

Answer 1

Since the magnetic field from the larger coil is constantly changing, the flux in the smaller coil is also changing. This leads to an induced EMF in the coil due to Faraday’s Law.

Question 2

What happens as a coil is rotated through a magnetic field?

Answer 2

The flux linkage decreases therefore the rate of change of flux decreases and so does the induced EMF across it.

Question 3

How can you deduce whether the temperature of a gas is constant during a compression?

Answer 3

In Boyle’s law, pV = constant for an isothermal change therefore, if it is shown to be not constant, neither is the temperature.

Question 4

What is the first law of thermodynamics?

Answer 4

The change in internal energy = The work done on or by the gas + The heat transfer to or from the gas.

Question 5

Why is the separation of equipotentials closer to the earth closer together even though the potential difference is constant?

Answer 5

As the gravitational field strength is stronger towards the earth and it is inversely proportional to the distance, as strength increases, separation must be smaller.

Question 6

How would the orbital frequency of an electron differ to the orbital frequency of a deuterium nucleus which consists of a proton and a neutron?

Answer 6

Since the charge is the same, the electrostatic force is the same therefore the frequency is unchanged. The weight of the extra neutron does not affect the centripetal force.

Question 7

In terms of the flow of electrons, how does a capacitor become charged?

Answer 7

Electrons experience a force from the negative terminal and flow onto the positive capacitor plate. Electrons are pushed of the negative capacitor plate.

Question 8

Why does the current decrease during the charging process of a capacitor?

Answer 8

Current is the rate of flow of charge and current is driven by a potential difference. As charge increases on the capacitor, it opposes the cells potential difference and reduces the overall potential difference which pushes the electrons on the plate. This means the rate of flow of electrons will decrease.

Question 9

Why is water usually selected as a coolant?

Answer 9

It has a high thermal conductivity.

Question 10

Why is graphite usually selected as a moderator?

Answer 10

It is chemically unreactive at high temperatures.

Question 11

Why is concrete usually chosen for shielding?

Answer 11

It also absorbs gamma as it has a high atomic number and density.

Question 12

How do you find the mass of one molecule?

Answer 12

Molar mass/Avogadro’s constant

Question 13

What does the N and m signify in the kinetic theory equation and how do you find m?

Answer 13

Number of molecules and the mass of one molecule.
Molar mass/Avogadro’s constant = Mass of one molecule

Question 14

How is gamma radiation emitted from the nucleus?

Answer 14

The nucleus de-excites from a high energy level to a lower energy level and emits a photon of gamma radiation.

Question 15

Why does a proton follow a parabolic path when accelerated through a uniform electric field?

Answer 15

It is repelled by the top plate therefore experiences a constant vertical acceleration. As the horizontal velocity is constant, the parabolic motion is formed.

Question 16

How do eddy currents arise in a transformer and how do they contribute to the inefficiency of the transformer?

Answer 16

The changing magnetic flux in the iron core leads to an induced EMF in the iron core which leads a current to flow.
The current causes dissipation of thermal energy in the core.

Question 17

What are 2 causes of thermal dissipation in an iron core of a transformer?

Answer 17

Mechanical vibrations and resistance of the wires

Question 18

What orbits are used for satellites sending TV signals down to Earth?

Answer 18

Equatorial, geosynchronous orbits

Question 19

If the angular frequency of a rotating coil in a magnetic field is doubled, what effect does this have on the alternating current?

Answer 19

The peak induced emf would double therefore the peak current would also double.
Doubling angular frequency also doubles the frequency of rotation so the frequency of the AC will also double.

Question 20

Why is a larger force required to move a magnet through a coil as it approaches one?

Answer 20

As the magnet approaches the coil, an emf is induced in the wire.
Due to Lenz’s law, a current will flow around the coil such that it opposes the motion of the magnet (The change the caused it).
Tis means a north pole is created on the bottom of the coil which repels the magnet.

Question 21

How would you describe the motion of air particles in a sealed cubic room?

Answer 21

The particles would travel at a range of speeds and would be constantly changing direction (Zigzag)

Question 22

Why may some of the water evaporate before the temperature of a flask of water reaches 100 degrees?

Answer 22

Temperature is only a measure of the sum of the average kinetic energies of its particles.
This means there will be faster particles which can convert their KE to PE and escape the surface of the water.

Question 23

What is the internal energy of an ideal gas?

Answer 23

It is only the sum of the average kinetic energies of its particles since potential energies of particles in an ideal gas are neglibible compared to their KE’s.

Question 24

What causes a baloon on top of a flask to deflate if the flask is place in an ice bath?

Answer 24

There is a pressure difference between the air and the baloon which presses it down into the flask and inflates it.

Question 25

Why would the volume of a bottle be smaller at the bottom of a mountain rather than the top?

Answer 25

At the top of the mountain air pressure and temperature is the same inside and out so the rate of collisions inside the bottle is same as the outside.

At ground level, the temperature is the same but the air pressure around the bottle is greater so the rate of collisions outside the bottle is greater resulting in a large inward force which derforms the bottle.

As the volume decreases, the rate of collisions with the walls of the container increases until the pressure inside matches the pressure outside.

Question 26

How can we achieve a constant power output from a thermal nuclear reactor?

Answer 26

Each fission must only lead to one other fission reaction.
This will achieve a constant rate of energy.