Exercise 13.3

Exercise 13.3: use Fleming's right-hand rule to find and mark the direction of the induced current in the conductor in each case.

Figure to be added

Exercise 13.3 — (i)-(iv): a wire AB, joined to a galvanometer G, runs from the front (A) to the back (B) through the gap between two block magnets and is moved down or up; (v)-(viii): a wire seen end-on as a dot between two poles, moved up or down.

How to read the diagrams

Find the field in the gap: it runs from the N face to the S face that face each other.
Right hand: thumb along the motion, first finger along the field; the middle finger gives the current.

Case	Field in the gap	Motion	Induced current
(i)	right to left	down	A to B
(ii)	left to right	down	B to A
(iii)	right to left	up	B to A
(iv)	left to right	up	A to B
(v)	N left to S right	up	into the page ⊗
(vi)	N right to S left	up	out of the page ⊙
(vii)	N left to S right	down	out of the page ⊙
(viii)	N right to S left	down	into the page ⊗

Why the answers come in pairs

In (i) the magnets are arranged so that the N face on the right faces the S face on the left, so the field in the gap runs from right to left. In (ii) both magnets are turned round, so the field reverses — and the current reverses. In (iii) the motion reverses instead, and again the current reverses. In (iv) both change, and the current is back as in (i). The end-on cases (v)–(viii) follow the same pattern. Just as with the left-hand rule, changing one thing flips the answer and changing two brings it back, which is a quick check on your hand.

In (i)–(iv), A is the end of the wire nearer to you and B the end further away, as drawn; the answers depend on that reading of the figure.