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Current electricity

Example 2.11

R R x A metre bridge is set up as shown in
Figure 2.32 using a standard 10 
resistor. The galvanometer shows zero
deflection when the Jockey contact is
G
FOR ONLINE READING ONLY
Jockey
at 48 cm from end A. Determine the
resistance of a resistor, X.
l l
1 2

S E

Figure 2.31

2. Set R to 1 Ω, then close the switch,
S, and slide the jockey over the metre
bridge wire until the galvanometer Figure 2.32
reads zero. Record length l and .l 2 Solution
1
3. Repeat step 2 for R = 2 Ω, 3 Ω, 4 Ω From the metre bridge expression,
and 5 Ω. Read and record the value L
of l and l in each case. X  L A  R
1
2
4. Use spreadsheet or otherwise to B
record results using Table 2.7. where
R  10  , L = 48 cm and
A
Table 2.7 L = 52 cm
Resistor, l (cm) l (cm) l 1 B
R (Ω) 1 2 l 2 Hence,

1 X  48 cm  10  9.23 
2 52 cm
3 Therefore, the resistance X is 9.23 .
4
5
Potentiometer
Questions A potentiometer is a reliable tool for

(a) Using ICT software or otherwise, measuring e.m.f. It consists of a length
l AB of uniform resistance wire, with a
plot a graph of R against 1 .
l 2 steady current flowing through it from an
(b) Deduce the value of unknown accumulator C (Figure 2.33). Any length
resistance, R X . from A is read from a metre rule AB, and
the length of AB may be one metre.

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Physics Form 2 Final.indd 63 25/10/2025 10:26