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  4. A torch bulb rated as 4.5 W , 1.5 V is connected as shown in fig. the e.m.f. of the cell, needed to make the bulb glow at full intensity is :

Q. A torch bulb rated as is connected as shown in fig. the e.m.f. of the cell, needed to make the bulb glow at full intensity is :

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Solution:

Resistance of bulb is given as

The equivalent of and in parallel combination which is connected across the battery is given as

Current drawn from battery is given as

Current through the bulb is

For correct power dissipation in the bulb we use

Questions from Current Electricity

1. Two sources of equal emf are connected to an external resistance . The internal resistances of the two sources are and If the potential difference across the source having internal resistance , is zero, then :

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2. In the network shown in figure, each resistance is equal to . The resistance between the points and is

3. A letter ' ' is constructed from a uniform wire with resistance per The sides of the letter are and the cross piece in the middle is long. The apex angle is The resistance between the ends of the legs is

4. The diagrams show five different ways in which currents can combine at a junction.

For which of these junctions, is the following equation correct ?

5. A battery of emf, is connected to resistances as shown in figure. The potential difference between the points and is

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