Question
(a) Two straight, vertical wires X and Y pass through holes in a horizontal card.
Fig. 8.1 shows the card viewed from above.
There is a current in each wire in a downward direction (into the page).
(i) The magnetic field at Y due to the current in X produces a force on Y.
Place a tick in each blank column of the table to indicate the direction of this magnetic
field and the direction of the force.
(ii) State and explain whether there is also a force on wire X.
(b) Fig. 8.2 shows a d.c. supply connected to the input of a transformer.
When switch S is first closed, the needle of the galvanometer deflects briefly, then returns to zero.
Explain why the brief deflection occurs.
Answer/Explanation
Answer:
(a)(i) Magnetic field at Y: ‘towards the bottom of the page’ ticked
Force at Y: ‘to the left’ ticked
(a)(ii) There is a force on X
because of the (magnetic) field caused by Y
OR due to the (magnetic) field around/ of Y
OR the (magnetic) fields due to X and Y interacting
(b) Change in current/ field is brief/ for short time/ occurs as switch
closes
Changing magnetic field/ flux links with secondary coil/ other coil/
core OR field/ flux lines cut coil
Causes induced voltage/ current