ELECTROMAGNETISM
4 marks · NormalA straight wire carries a current vertically upwards. Plotting compasses are placed in a horizontal plane around the wire.
Describe the shape of the magnetic field around the wire.
State and use the right-hand grip rule to find the direction of the field when looking from above.
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) The magnetic field forms concentric circles around the wire. · must show Concentric circles
(b) The right-hand grip rule states that if the right thumb points in the direction of the current (upwards), the fingers curl anticlockwise when viewed from above; so the magnetic field is anticlockwise. · must show Correct use of right-hand grip rule, Direction is anticlockwise from above
Common mistakes: Confusing direction of field
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · States or describes field shape is concentric circles around the wire.
A1 (a) · 1 mark · States field is in horizontal plane/perpendicular to wire.
B1 (b) · 1 mark · States correct use of right-hand grip rule (thumb current, fingers field).
A2 (b) · 1 mark · Gives direction is anticlockwise when viewed from above.
Worked solution
(a) The magnetic field forms concentric circles in the plane perpendicular to the wire (horizontal plane).
(b) The right-hand grip rule: if you point your right thumb up (current), your fingers curl in the direction of the field: anticlockwise as seen from above.