Question 18: Current Electricity

Question

In the arrangement shown in figure, when the switch S
2
is open, the galvanometer, shows no deflection for $$l$$ = 50 cm when the switch S
2
is closed, the galvanometer shows no deflection for $$l$$ = 0.416 m. The internal resistance (r) of 6 V cell is

Accepted Answer

When S
2
open.
Assume resistance of XY = R.
Resistance of wire per unit length, x = $$\frac{R}{L}$$ = R $$\Omega$$ m
$$-$$1
$$\because$$ I = E
0
/ R
Now, the potential drop across 50 cm length is 6 V, so
$$\frac{E_0}{R}$$ $$	imes$$ R $$	imes$$ $$\frac{50}{100}=6$$
$$\Rightarrow$$ E
0
= 12 V
When S
2
closed, potential drop across 0.416 cm length,
V
1
= $$\frac{E_0}{R}	imes$$ R $$	imes\,0.416=12	imes0.416\approx 5$$ V
Hence, E $$-$$ Ir = 5V
$$\Rightarrow$$ 6 $$-$$ Ir = 5
$$\because$$ I = $$\frac{5}{10}$$
$$	herefore$$ 6 $$-$$ = $$\frac{5}{10}$$r
$$\Rightarrow$$ r = 2$$\Omega$$

Answer

2 $$\Omega$$

Answer

3 $$\Omega$$

Answer

5 $$\Omega$$

Answer

9 $$\Omega$$

Current Electricity

In the arrangement shown in figure, when the switch S 2 is open, the galvanometer, shows no deflection for $l = 50 cm when the switch S 2 is closed, the galvanometer shows no deflection for l$ = 0.416 m. The internal resistance (r) of 6 V cell is

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