Current Electricity Ques 73
- On interchanging the resistances, the balance point of a meter bridge shifts to the left by $10$ $ cm$. The resistance of their series combination is $1 $ $k \Omega$. How much was the resistance on the left slot before interchanging the resistances?
(2018 Main)
(a) $990 $ $\Omega$
(b) $910 $ $\Omega$
(c) $900 $ $\Omega$
(d) $550 $ $\Omega$
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Answer:
Correct Answer: 73.(d)
Solution:
Formula:
- $ \frac{R _1}{R _2}=\frac{l}{100-l} $ $\quad$ …….(i)
and $\quad \frac{R _2}{R _1}=\frac{l-10}{100-(l-10)}$ $\quad$ …….(ii)
From Eqs. (i) and (ii),
$ \Rightarrow \quad l=55 $ $cm $
Substituting in Eq. (i), we get
$ \frac{R _1}{R _2}=\frac{55}{45} $ $\quad$ \text{(iii)}
Further,
$ R_1+R_2=100\ \Omega $ $\quad$ …….(iv)
Solving equations (iii) and (iv),
$ R _1=550 $ $\Omega $
BETA
