Page 70 - Physics_Form_2

Physics for Secondary Schools

C cells, jockey, connecting wires,
switch, accumulator
l
A B
Procedure
S
1. Set up the potentiometer circuit as
shown in Figure 2.34 where C is an
FOR ONLINE READING ONLY
E G
accumulator, E and E are the two
2
1
Figure 2.33: A potentiometer cells for comparison.
On closing the switch, S, there will C S
be a potential drop across AB and l 1 l 2 N M
hence between point A and any A
other point along AB. This potential P J B
drop will produce a current in the G J
galvanometer in the direction AGJ so Q E 1 G
that, in whatever position of J on AB, E
the galvanometer will be deflected. 2 Figure 2.34
Suppose a second cell E, is introduced
in series with the galvanometer, its 2. Join the positive terminal of P to A,
current in the direction JGA, will now the same terminal to which the positive
be opposed by the current due to the terminal of C is joined.
cell D flowing in the direction AGJ. 3. Join the negative terminal of P to a slider,
There will now be two opposing p.d J, through a galvanometer, G.
between A and J. It should be possible
to find a position, J, of the jockey on 4. Gently tap on the wire with J, find the
AB for which the p.d across AJ due point N (balance point) when no current
to E balances the p.d across AJ due to flows in G. Measure the balance length
D. Activity 2.9 illustrate how one can AN or l from the metre rule.
1
compare e.m.f. of two cells by using 5. Disconnect the cell P ( E ) from the
1
potentiometer. circuit, and replace it with cell Q ( E ),
2
the other cell for comparison. As before,
obtain the new balance point M and read
Activity 2.9
off the length AM or .l
2
Aim: To compare the e.m.f
of two cells using a Questions
potentiometer (a) Suppose the value of E is known, find
1
the value of E .
Materials: A slide-wire (b) It is clear from this activity that, as
2
potentiometer, the e.m.f. increases, the length of the
galvanometer, 2 dry potentiometer wire increases as well.

64
Student’s Book Form One

Physics Form 2 Final.indd 64 25/10/2025 10:26