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2 marksMagnetic Forces

CAPE Physics Unit 2 · 2011 · Paper 2 · Question 1(c)(iv)

A narrow beam of electrons travels at speed v into a uniform electric field between oppositely charged parallel plates separated by distance d (top plate at potential V relative to lower plate). A magnetic field is applied perpendicularly to cancel the deflection.

The magnetic flux density is now doubled. The distance between the plates is then adjusted so that no deflection occurs. Calculate the new distance.

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Other parts of this question

  1. 1(a)Define magnetic flux density, B, in terms of the force on a current-carrying wire.[2 marks]
  2. 1(b)Draw the resultant magnetic field pattern between the two flat permanent magnets in Figure 1 (b) with wire P carrying current perpendicularly into the plane of…[4 marks]
  3. 1(c)(i)State the direction of the magnetic field.[1 mark]
  4. 1(c)(ii)By considering the forces on EACH electron, show that the magnetic flux density is given by B = V / (v d).[4 marks]
  5. 1(c)(iii)Given that V = 3500 V, v = 2.8 * 10^7 m s^-1, and d = 50 mm, calculate the magnetic flux density of the magnetic field.[2 marks]

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