Question
(a) The box lists four materials.
Use words from the box to answer parts (i) and (ii).
Each word may be used once, more than once or not at all.
State all materials that are electrical insulators.
……………………………………………………………………………………………………………………. [1]
State one example of a magnetic material.
……………………………………………………………………………………………………………………. [1]
(b) Fig. 9.1 shows two magnets, P and Q, which are repelling each other.
On magnet P, the N pole is labelled N.
On Fig. 9.1, label the other pole on magnet P and both poles on magnet Q. [1]
(c) One advantage that electromagnets have, compared with permanent magnets, is that their
strength can easily be altered.
State one other advantage of an electromagnet compared with a permanent magnet.
…………………………………………………………………………………………………………………………… [1]
(d) A student wants to make the strongest electromagnet possible.
Indicate which properties produce the strongest electromagnet. Tick (3) one box in each list.
[3] [Total: 7]
Answer/Explanation
Ans: (a)(i) plastic AND wood
(a)(ii) iron
(b)N S S N
(c)(electromagnet can be) switched off OR switched on
(d) feature 1: top box ticked (200 turns) feature 2: middle box ticked (iron) B1feature 3: bottom box ticked (3.0A)
Question:
Fig. 8.1 shows two vertical, cylindrical tubes and a cylindrical magnet all held in a vacuum.
One tube is made of plastic and the other tube is made of copper. The two cylindrical tubes have identical dimensions.
The magnetic field of the small, cylindrical magnet is extremely strong.
Initially, the magnet is at rest at the top of the plastic tube.
The magnet is released and it falls through the plastic tube without experiencing a resistive force.
The magnet takes 0.67 s to fall to the lower end of the plastic tube.
(a) The mass of the magnet is 0.012 kg.
Calculate the kinetic energy of the magnet when it reaches the lower end of the plastic tube.
kinetic energy = …………………………………………………
Answer/Explanation
Ans: 0.27 J
(v =) at (in any form) or 10 × 0.67 or 6.7 (m / s)
6.7 (m / s)
(KE =) ½mv 2 (in any form) or ½ × 0.012 × (10 × 0.67) 2
or ½ × 0.012 × 6.7
(b) The magnet is then held at the top of the copper tube and released. As it falls through the copper tube, an electric current is generated in the copper.
(i) Explain why there is a current in the copper.
Answer/Explanation
Ans: magnetic field / magnetic field lines cut the copper / tube / it (or vv.)
electromagnetic induction occurs or e.m.f. induced
(ii) The current in the copper produces a magnetic field of its own in the tube.
The magnet falls much more slowly in the copper tube than in the plastic tube.
Explain why the magnet falls more slowly in the copper tube.
Answer/Explanation
Ans: (upwards / opposing) force on magnet
force / magnetic field / e.m.f. / current opposes the change (producing it) / opposes motion or force on magnet due to magnetic field caused by current in tube