Questions

Question 1

What happens to the brightness of a lamp when a variable resistor is connected in parallel?

Answer 1

(resistance increases)
- Reduces current in battery
- Reduces lost volts and increases terminal p.d.
- Lamp becomes brighter

Question 2

What properties/stress-strain characteristics
should a material used for bungee jumping have?

Answer 2

• Large Tensile strain for a given stress.
• ∵ Time taken to come to rest lengthens

Question 3

Why would a wire no longer return to its’ original shape after usage?

Answer 3

wire is stretched beyond elastic limit/ Deform plastically.
- Results in permanent deformation

Question 4

How is a stationary wave formed and why can stationary waves only be certain frequencies?

Answer 4

• wave travels along string and is reflected at each end
• these two coherent waves superpose resulting in the formation of nodes & anti-nodes.
• only certain frequencies because fixed ends have to be nodes

Question 5

What happens to the brightness of a lamp when a variable resistor is connected in series?

Answer 5

• resistance increases
• reduces current through lamp
• lamp dimmer

Question 6

Explain why resistivity of a wire changes with temperature

Answer 6

• Resistance/resistivity increases with increasing temperature.
• (lattice) ions vibrate with greater amplitude
• rate of movement of charge carriers/electrons (along wire)
  is reduced. (for given p.d.)

Question 7

• What properties does this material have and how does this graph show that?

Answer 7

• Brittle
  ↳ little to no plastic behaviour
• Stiff
  ↳high Young Modulus
  ∵ steep gradient

Question 8

What is meant by an EMF of _V for a battery?

Answer 8

• The amount of energy transferred from chemical energy to electrical energy (for every coloumb of charge).
• _J of energy per coloumb of charge.

Question 9

At the instance a free falling object has been caught what is the direction of its velocity, acceleration and pull force?

Answer 9

• the velocity is downwards because the object is falling toward the ground
• The net force is upwards
• the system (object) accelerates in the same direction as the net force so the boxes acceleration is upwards
• since the object’s velocity and acceleration are in opposite directions, the box slows down.

Question 10

What is the Internal Energy of a Gas

Answer 10

• It is the sum of the kinetic and potential energies of the particles/atoms/molecules

Question 11

Absolute zero of temperature can be interpreted in terms of ideal gas laws or the kinetic energy of particles in an ideal gas

describe these two interpretations of absolute zero of temperature

Answer 11

• For kinetic energy: the temperature at which the random motion stops and the kinetic energy is zero
• For Ideal gas: the temperature at which the volume/pressure of a gas extrapolates to zero
  where volume and temp are related by Charles’ law and pressure and temp by the pressure law

Question 12

Explain why the kinetic energy of neutrons must be reduced in a thermal nuclear reactor

Answer 12

• To increase the probability/chance of fission when a neutron collided with fissile material

Question 13

When dropping the kinetic energy of a neutron in a thermal nuclear reactor it is reduced from 2MeV to ~1eV

Explain why the number of collisions needed to do this depended on the nucleon number of the moderator atoms

Answer 13

• More kinetic energy is lost when the mass of the moderator nucleus is closer to the mass of the neutron
• so the number of collisions needed increases with nucleon number