Page 198 - NCERT Science Class 10 English Medium

E X E R C I S E S

1. A piece of wire of resistance R is cut into five equal parts. These parts are then
connected in parallel. If the equivalent resistance of this combination is R′, then the
ratio R/R′ is –
(a) 1/25 (b) 1/5 (c) 5 (d) 25
2. Which of the following terms does not represent electrical power in a circuit?
2
2
(a) I R (b) IR 2 (c) VI (d) V /R
3. An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the
power consumed will be –
(a) 100 W (b) 75 W (c) 50 W (d) 25 W
4. Two conducting wires of the same material and of equal lengths and equal diameters
are first connected in series and then parallel in a circuit across the same potential
difference. The ratio of heat produced in series and parallel combinations would be –
(a) 1:2 (b) 2:1 (c) 1:4 (d) 4:1
5. How is a voltmeter connected in the circuit to measure the potential difference between
two points?
–8
6. A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10 Ω m. What will be
the length of this wire to make its resistance 10 Ω? How much does the resistance
change if the diameter is doubled?
7. The values of current I flowing in a given resistor for the corresponding values of
potential difference V across the resistor are given below –
I (amperes) 0.5 1.0 2.0 3.0 4.0
V (volts) 1.6 3.4 6.7 10.2 13.2
Plot a graph between V and I and calculate the resistance of that resistor.
8. When a 12 V battery is connected across an unknown resistor, there is a current
of 2.5 mA in the circuit. Find the value of the resistance of the resistor.
9. A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω , 0.5 Ω
and 12 Ω, respectively. How much current would flow through the 12 Ω resistor?
10. How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line?
11. Show how you would connect three resistors, each of resistance 6 Ω, so that the
combination has a resistance of (i) 9 Ω, (ii) 4 Ω.
12. Several electric bulbs designed to be used on a 220 V electric supply line, are
rated 10 W. How many lamps can be connected in parallel with each other across
the two wires of 220 V line if the maximum allowable current is 5 A?
13. A hot plate of an electric oven connected to a 220 V line has two resistance coils
A and B, each of 24 Ω resistance, which may be used separately, in series, or in
parallel. What are the currents in the three cases?
14. Compare the power used in the 2 Ω resistor in each of the following circuits:
(i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and (ii) a 4 V battery in parallel
with 12 Ω and 2 Ω resistors.

Electricity 193

2024-25