Page 49 - CHAPTER-1 (Electricity)

CHAPTER 1

ELECTRICITY

4. Show how we can connect three resistors, each of resistance 6 ,

so that the combination formed has a resistance of

(i) 2 (ii) 9 .

Ans. (i) In order to get a resistance of 2 from three resistors, each

of resistance 6 , we connect all the three resistors in parallel as

shown in figure. Thr equivalent resistance in parallel combination,

6
i.e., R is given by R = = 2 .
p
p
3
(ii) To obtain a resistance of 9 from three resistors, each of
resistance 6 , we can connect two resistors in parallel and then

this parallel combination (or resistance 3 ) in series with the third

resistor as shown in fig.

6
  
C D
A B A C D B
6 ( a)

6

6 
A B A B

6
( b)

5. Various electric bulbs are designed to be used on a 220 V electric

supply line, rated at 10 W. The maximum number of lamps that

can be connected in parallel combination with one another

across the two wires of 220 V line such that the maximum

allowable current is 5 A?

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