Chapter 11:  Electricity

Class 10 Science Chapter 11 :  Electricity Questions and Answers :

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

Answer: (d) 25

[  When a wire of resistance R is cut into five equal parts and these parts are connected in parallel,

 Let R be the resistance of each of the five equal parts .

Since the five equal parts are cut from the original wire of resistance R, each part's resistance will be .

Therefore, the correct answer is (d) 25. ]
2. Which of the following terms does not represent electrical power in a circuit?

(a)    (b)      (c)    (d)

Answer:  (b)      
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

Answer:  (d) 25 W

[ The electric bulb is rated at 220 V and 100 W.

 Let, R be the first resistance  :

The power consumed (P') when the bulb is operated at 110 V:

So, the power consumed by the electric bulb when operated on 110 V is 25 W.

The correct answer is (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

Answer:  (c) 1 : 4

[  Let R be the resistance of each conducting wire .

When the wires are connected in series, the total resistance

When the wires are connected in parallel, the total resistance ,

The formula for heat produced in a resistor is given by:

The ratio of heat produced in series to parallel combinations would be:

And 

So, the ratio of heat produced in series to parallel combinations is 4 : 1.

The correct answer is (d) 1 : 4 ]