# Moving wire over a Square Frame!

Electricity and Magnetism Level 4

$$ABCD$$ is a square frame made from different wires of same length and each having different uniform resistance per unit length. Resistances of wires forming sides $$AB, BC, CD$$ and $$DA$$ are $$100W, 400 W, 500 W$$ and $$200 W$$ respectively. An ideal cell is connected across $$B$$ and $$D$$. A straight conducting wire containing a resistance and a galvanometer in series starts rotating about pivoted point $$A$$ from initial position as shown with uniform angular velocity $$\omega = \frac{\pi}{360} rad/sec$$. One end of the straight wire (rotating) is pivoted at $$A$$ and other end always in sliding contact with a side of the square. The time (in seconds) after start when galvanometer shows zero deflection is?

×