(a)(i) What is meant by neutral point in a magnetic field?
(ii) Draw and label a diagram to show the pattern and direction of the magnetic field produced around a straight current-carrying wire.
(b) When is an ammeter said to be (i) Sensitive (ii) accurate?
(c)(i) Explain, using a labelled diagram, how a delicate magnetic material could be protected, from the Earth’s magnetic field.
(ii) A charge of 1.6 x 10(^{-19}) C enters a magnetic field of flux density 2.0 T with a velocity of 2.5 x 10(^7) ms(^{-1}) at an angle of 30° with the field. Calculate the magnitude of the force exerted on the charge by the field.
(d) State the laws of electro-magnetic induction.
Explanation
(a) (i) Neutral point is a point at which the resultant magnetic flux density is zero.
(ii)
(b)(i) (ii) An ammeter is accurate if the current it mea-sures is close to the true value of the current flowing through the instrument.
(c)
The material is surrounded by a thick wall of ferro-magnetic material which does not allow magnetism to pass through them. This shields or protects the material from the earth’s magnetic field.
(ii) F = qvBsin(theta) = 1.6 x 10(^{-19}) x 2.5 x 10(^{7}) x 2 x 0.5 = 4 x 10(^{2}) N
(d) Electromagnetic induction laws are
– Whenever there is a change in the magnetic flux linked with a circuit, an e.m.f is induced, the magnitude of which is proportional to the rate of change of the flux linked with the circuit.
– The direction of the induced current is always such as to oppose the change producing it.