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1 markMagnetic Forces

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

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.

State the direction of the magnetic field.

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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)(ii)By considering the forces on EACH electron, show that the magnetic flux density is given by B = V / (v d).[4 marks]
  4. 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]
  5. 1(c)(iv)The magnetic flux density is now doubled. The distance between the plates is then adjusted so that no deflection occurs. Calculate the new distance.[2 marks]

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