A student explores the field between magnets. Figure 9 shows two magnet ends facing one another, a north pole on the left and a south pole on the right.
(a)(i) Iron filings can show a field's pattern. Name a different piece of equipment for investigating the field.
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A plotting compass. Its needle lines up with the field, so moving it around the magnets shows the field direction at each point.
How the marks are earned
- A plotting compass. Iron filings and a pencil earn nothing. A second magnet earns the mark only if its use is explained, for example by noting which way it is pushed or pulled.
(a)(ii) Sketch the magnetic field lines in the gap between the two poles shown in Figure 9.
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The drawing must show four or more lines running across the gap from the face of the north pole on the left to the face of the south pole on the right. The two middle lines are straight and parallel. The next line above and the next line below curve outwards, bulging away from the middle before meeting the poles. Every line carries an arrowhead pointing to the right, from north to south.
How the marks are earned
- One mark: at least 2 field lines drawn across the gap, joining the north pole to the south pole. Lines to unseen poles or back to the same magnet do not count, but they do not cancel the mark.
- Shape mark: four or more lines in the gap, with the middle two running straight across and the outer pair bowing outwards, one above and one below. Straightness and curvature are judged by eye.
- Direction mark: show the field's direction with an arrowhead on at least one line, heading from the north pole to the south pole. No line may carry an arrow that says the opposite.
Why it scores
Field lines always run from a north pole to a south pole. They are straight and evenly spaced where the field is strongest, in the middle of the gap, and they bow outwards towards the edges where the field spreads out and weakens.
Revise Magnetic Fields(b)(i) A solenoid is made by winding copper wire round an iron nail. Why is the wire insulated?
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The insulation stops current crossing between neighbouring turns, or into the iron nail, so a short circuit is avoided and the current goes all the way round the coil.
How the marks are earned
- Any one of: to avoid a short circuit; to stop current flowing in the iron nail; to stop the nail becoming live. Unqualified safety, danger, heat or shock earn nothing.
(b)(ii) Give one thing that changes the strength of a solenoid's magnetic field.
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The number of turns of wire. More turns in the coil make a stronger field. A larger current, or an iron core, would also strengthen it.
How the marks are earned
- Any one: the number of turns of wire, the length of the wire, the current, the potential difference, the thickness (cross-sectional area) of the wire, or changing or removing the iron core.