Level 1: Remove the Middle Resistor of a Bridge: Does R Change?
Different resistors. Spot the balance.
In a bridge between A and B, the arms are A–C = 1 Ω, C–B = 2 Ω, A–D = 2 Ω and D–B = 4 Ω, and a 5 Ω resistor joins C and D. The equivalent resistance between A and B is:
First check for balance: the arms on the upper path are in the ratio 1 : 2, and the arms on the lower path are in the same ratio, 2 : 4. So C and D are at the same potential and the 5 Ω resistor carries no current.
Once the bridge is balanced, the value of the middle resistor does not matter, so the 5 Ω can be ignored. The two paths of 3 Ω and 6 Ω in parallel give 2 Ω.
Every Level 2 starts from a quick question, Level 1, and changes one thing. Seeing what that change does is the skill JEE Main tests. Try it here, free and with no signup, then read the worked answer.
