# Magnetism: Current flowing through a resistor, surface charge distribution, constant speed of the bar

A metal bar of mass m and length L slides without friction but with good electrical contact between two vertical metal posts. The bar and posts have negligible resistance. The posts are connected at the bottom by a resistor R.

Assume the bar falls at constant speed v, and that there is a magnetic field coming out of the page.

(a) Calculate the current flowing through the resistor.

(b) Clearly show the surface charge distribution on the entire circuit (both sign and gradient). Explain how that surface charge distribution causes a current to flow in the circuit.

(c) How can the speed of the bar be constant if it is falling? Calculate the speed v.

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A metal bar of mass m and length L slides without friction but with good electrical contact between two vertical metal posts. The bar and posts have negligible resistance. The posts are connected at the bottom by a resistor R.

Assume the bar falls at constant speed v, and that there is a magnetic field coming out of the page.

(a) Calculate the current flowing through the ...

#### Solution Summary

The solution clearly explains the problems and then shows all the formulas and calculations used to arrive at the answers.