In a meter bridge experiment to determine the value of unknown resistance, first the resistances 2 Ω and 3 Ω are connected in the left and right gaps of the bridge and the null point is obtained at a distance l cm from the left. Now when an unknown resistance x Ω is connected in parallel to 3 Ω resistance, the null point is shifted by 10 cm to the right of wire. The value of unknown resistance x i s ___ Ω.
Physics · Current electricity · electric instruments
JEE Mains 2026 24 January Evening Shift

Question

In a meter bridge experiment to determine the value of unknown resistance, first the resistances 2 Ω and 3 Ω are connected in the left and right gaps of the bridge and the null point is obtained at a distance l cm from the left. Now when an unknown resistance x Ω is connected in parallel to 3 Ω resistance, the null point is shifted by 10 cm to the right of wire. The value of unknown resistance x i s ___ Ω.

Physics · Current electricity · electric instruments

JEE Mains 2026 24 January Evening Shift

G1 Physics · Accepted Answer

Initially, 2/3 = l/(100-l). Therefore, 2(100-l) = 3l. Hence, l = 40 cm. After connecting the unknown resistance x in parallel with 3 Ω, let the new right-gap equivalent resistance be R. The new balance point is l+10 = 50 cm. Therefore the remaining wire length is also 50 cm. At balance, 2/R = 50/50 = 1. Hence, R = 2 Ω. Now, R = 3x/(3+x). Therefore, 2 = 3x/(3+x). Thus, 6+2x = 3x, so x = 6 Ω. Hence the answer is 6.