Magnetism and Electromagnetism
6 marks · NormalA student investigates how to create a uniform magnetic field using two bar magnets in the laboratory.
Describe and draw the arrangement of two bar magnets to produce a uniform magnetic field between them.
Explain why the field in the region between the magnets is described as 'uniform'.
Give one use of a uniform magnetic field in a scientific or technical device.
Suppose the magnets are moved further apart. Describe what happens to the uniform region.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) — · must show Bar magnets with N facing S, field lines straight and parallel between them
(b) The field is the same strength and direction everywhere between the poles; field lines are parallel and evenly spaced.
(c) In cathode ray tubes / mass spectrometers / particle accelerators / MRI scanners / other scientific device with uniform field.
(d) The uniform region becomes smaller (or disappears) as the distance increases.
Must show: magnets placed with opposite poles facing
Show mark scheme and worked solution
Marking points
B3a (a) · 2 marks · Arrangement: magnets with N and S facing, uniform lines parallel and evenly spaced between (1). Clear labelling (1).
B3b (b) · 2 marks · Explains meaning of uniformity: strength and direction constant, lines parallel and evenly spaced (1 each).
B3c (c) · 1 mark · Correct scientific/technical use (1).
B3d (d) · 1 mark · Describes reduction or loss of uniform region as magnets are separated (1).
Worked solution
a) (Student should draw two bar magnets with N and S poles facing each other closely, lines straight between them.)
b) The magnetic field is called "uniform" because its strength and direction are the same everywhere between the poles. The field lines are straight, parallel and evenly spaced.
c) Uniform magnetic fields are used in devices like cathode ray tubes or particle accelerators, to control the motion of charged particles.
d) As the magnets are moved further apart, the region of uniform field between them decreases in size and eventually disappears.