1. Tardigrade
  2. Question
  3. Physics
  4. A potentiometer PQ is set up to compare two resistances as shown in the figure. The ammeter A in the circuit reads 1.0 A when two way key K3 is open. The balance point is at a length l1 cm from P when two way key K3 is plugged in between 2 and 1, while the balance point is at a length l2 cm from P when key K3 is plugged in between 3 and 1. The ratio of two resistances (R1/R2), is found to be :

Question Error Report

Thank you for reporting, we will resolve it shortly

Back to Question

Q. A potentiometer $PQ$ is set up to compare two resistances as shown in the figure. The ammeter $A$ in the circuit reads $1.0\, A$ when two way key $K_3$ is open. The balance point is at a length $l_1$ cm from $P$ when two way key $K_3$ is plugged in between $2$ and $1$, while the balance point is at a length $l_2\, cm$ from $P$ when key $K_3$ is plugged in between $3$ and $1$. The ratio of two resistances $\frac{R_1}{R_2}$, is found to be :Physics Question Image

JEE MainJEE Main 2017Current Electricity

Solution:

When key is at point
$V_{1} = iR_{1} = xl_{1}$
when key is at (3)
$V_{2} = i \left(R_{1} + R_{2}\right) = xl_{2}$
$\frac{R_{1}}{R_{1}+R_{2}} = \frac{l_{1}}{l_{2}}$
$\frac{R_{1}}{R_{2}} = \frac{l_{1}}{l_{2}-l_{1}}$