Question
A student uses a bar magnet to distinguish between an unlabelled magnet and an iron bar.
(a) Describe how the student identifies which is the magnet and which is the iron bar.
(b) The student suspends the iron bar near to a coil, as shown in Fig. 10.1. The iron bar is free to move.
Describe and explain what happens when the switch S is closed.
(c) Fig. 10.2 shows a wire passing through a piece of card.
There is a current in the wire in the direction of the arrow.
On Fig. 10.3, draw the pattern of the magnetic field lines due to the current in the wire. Include the direction of the field.
Answer/Explanation
Answer:
(a) (bar) magnet is brought close to both ends (of one of unknown bars)
either
If both ends attract it is an iron bar
or
If one end repels it is a magnet
(b) iron bar moves toward coil
any two from:
• current in coil
• coil becomes an electromagnet
• soft iron attracted to coil
• iron bar becomes (an induced) magnet (with opposite pole nearest coil)
(c) at least one circle centred on wire (by eye)
two or more circles centred on wire (by eye)
arrow showing clockwise direction on at least one circle
Question
Fig. 11.1 shows a vertical conductor passing through a horizontal piece of card.
(a)(i) On Fig. 11.1, draw a cell and a switch in series with the conductor to form a complete circuit.
Use the correct circuit symbols.
(ii) A student sprinkles iron filings onto the card and closes the switch. There is a current in the conductor. Describe the pattern of the magnetic field seen.
(iii) The student reverses the direction of the current in the conductor. State the effect, if any, on the pattern he sees.
(b) Describe an experiment to show that a force acts on a current-carrying conductor in a magnetic field. Show how to arrange the equipment. Include a diagram in your answer.
Answer/Explanation
Answer:
(a)(i) cell and switch connected in series with any part of conductor (on Fig.11.1)
correct symbols used – (on Fig.11.1)
(ii) circular
around conductor/wire
(iii) no change/nothing
(b) conductor/wire between the poles of a magnet
opposite poles facing each other
current in wire
wire moves/Flemings left hand rule indicated