Magnetic Fields Questions

A

In the presence of a suitably directed uniform magnetic field, charged particles move at constant speed in a circular path of constant radius. By reference to the force acting on the particles, explain how this is achieved and why it happens. (4 marks)

B

A

Think about the gradient (its linearly increasing graph so will have a constant graph.) C

Think Velocity-time graph (the gradient would explain constant acceleration… then 0 acceleration)

D

A

D

D

C

B (same as c?)

Explain why a particle is accelerating even when it is moving with a uniform speed in a circular path. (2 marks)

• acceleration is (rate of) change of velocity

• velocity is changing since direction is changing

State, in words, the two laws of electromagnetic induction. (2 marks)

emf ∞ rate of change of flux (linkage) (Faradays Law)

direction of induced emf (or current) ✔ is such as to oppose the change (in flux) producing it ✔

Explain, using the laws of electromagnetic induction, how a device acts as an electromagnetic brake. (3 marks)

• Current in coil has its own magentic field.

• Rotating disc causes a change in magnetic flux which induces an emf

• Induced current interacts with magnetic field, causing a repulsion of like poles. (The induced emf generates eddy currents in the disc.

• By Lenz’s Law, these currents create their own magnetic fields that oppose the change in flux.

• This leads to a repulsion or braking effect, where the disc experiences a force resisting its motion.)