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INNOVA JUNIOR COLLEGE
JC 1 H2 Physics (2009/2010)
Tutorial 11: D.C. circuits
Equivalent resistance of multiple resistors
5. p136 Q8 N03/II/2
The variation with current of the
potential difference (p.d.) across a
component X is shown in Fig. 2.1.
(a) (i) State how the resistance of
component X varies, if at all, with
increase of current.
(ii) On Fig. 2.1, draw a line to show the
variation with current of the pd
across a resistor R of constant
resistance 3.0 .
(b) The component X and the resistor R of
resistance 3.0  are connected in
series with a battery of negligible
internal resistance, as shown in Fig. 2.2.
The current in the circuit is found to be 2.0 A.
(i) Use Fig. 2.1 to determine the pd
across component X.
(ii) Determine
1. the p.d. across R,
2. the emf of the battery.
(c) The resistor R and the component X are
now connected in parallel with the
battery, as shown in Fig. 2.3.
Use your answer to (b)(ii) and the graph
of Fig. 2.1, determine the current from
the battery.
Potential divider circuits
6. In the figure below, the two lamps L1
and L2 labelled 3.0 V, 0.25 A and 6.0 V,
0.05 A, respectively, light up with normal
brightness.
R1
3 V, 0.25 A
+
L1
L2
12 V
_
R2
6 V, 0.05 A
(a) Calculate the values of the resistance R1
and R2.
(b) What happens to L1 if L2 burns out first?
(c) What happens to L2 if L1 burns out first?
7. A thermistor has a resistance 3900
o
o
 at 0 C and resistance 1250  at 30 C.
The thermistor is connected into the
circuit below in order to monitor
temperature changes.
thermistor
1.50 V
R
V
The battery of e.m.f 1.50 V has
negligible internal resistance and the
voltmeter has infinite resistance.
o
(a) The voltmeter is to read 1.00 V at 0 C.
Show that the resistance of resistor R is
7800.
(b) The temperature of the thermistor is
o
increased to 30 C. Determine the
reading on the voltmeter.
(c) The voltmeter in the figure is replaced
with one having a resistance of 7800.
Calculate the reading on this voltmeter
for the thermistor at a temperature of
o
0 C.
8. The galvanometer reading is zero in
the circuit.
75 
8V
galvanometer
X
75 
2V
75 
What is the value of resistor X?
9. Fig. 9 shows a 120 V supply that is
connected to two loads A and B through
distribution wires of resistance per unit
length 1.00 x 10-4 Ω m-1. Load A is 200
m away from the supply, while load B is
a further 100 m away from load A.
(a) Calculate current I.
(b) Determine the potential
across load A and load B.
difference