Unit 4

Question 0

State one similarity and one difference between a particle and its antiparticle

Answer 0

Similarity= same mass

Difference= opposite charge

Question 1

The magnetic force F that acts on a current carrying conductor in a magnetic field is given by the equation

F=BIL

State the condition under which this equation applies

Answer 1

The magnetic field must be at right angles to the current

Question 2

In order to make an object move around a circular path at a constant speed a resultant force must act on it.
Explain why a resultant force is required and state the direction of this force.

Answer 2

• The velocity/ direction is changing

- towards the centre of the circle

Question 3

Direction of an electric field

Answer 3

Positive to negative

Question 4

What is meant by “Thermionic emission”?

Answer 4

Release of (surface) electrons due to heating

Question 5

model answer

Cyclotron (how electric and magnetic fields affect particles in a cyclotron) (5)

Answer 5

Electric fields:

• accelerate particles
• the polarity of the Dee’s switches every half cycle (alternating potential difference)

Magnetic fields:

• at right angles to the particles path
• maintains circular motion
• the radius of the circle increases as the particles speed increases

Question 6

model answer

Momentum (MOVING explosion) (4)

Answer 6

• no external force so momentum is conserved
• gains momentum in backwards direction so gains equal momentum in forwards direction
• kinetic energy of system increases
• some chemical energy is converted to KE

Question 7

*model answer*
Bubble Chamber (role of Electric and Magnetic fields) (5)

Answer 7

Electric fields:

• accelerates particles
• direction of force indicates sign of charge

Magnetic fields:

• produce circular motion/provide centripetal force
• direction of force/curvature indicates charge
• momentum/speed/mass found from radius
• r=p/BQ or Bqv=(mv^2)/r

Question 8

*model answer*
Induced EMF (could around motor) (4)

Answer 8

• There is a magnetic field causing the core to become an electromagnet
• The field/Flux is changing due to alternating current (AC)
• B field passes though rotor (field lines of flux are cut)
• The changing magnetic flux/field leads to an induced EMF

Question 9

model answer

Why does the motor turn? (Induced EMF) (2)

Answer 9

• rotor experiences a force F=BIL

- due to current in the rotor being in a magnetic field/rotor becomes a magnet

Question 10

model answer

How to increase speed motor turns? (Induced EMF) (3)

Answer 10

• increase number of turns in the coil
• increase magnitude of current
• increase frequency of current

Question 11

model answer

How can a metal disc be made to emit electrons? (2)

Answer 11

• Thermionic emission
• heating up metal by supplying a current
• electrons are emitted