# Electromagnetics question

1. Jul 15, 2008

### Hakins90

The problem statement, all variables and given/known data

The question is R12 of the book here - http://books.google.co.uk/books?id=...hl=en&sa=X&oi=book_result&resnum=10&ct=result

The attempt at a solution

Voltage induced, $$\epsilon = \frac{d\phi}{dt} = B\frac{dA}{dt} = BaV$$ (Using area swept out per second by a line of charge technique)

Resistance, $$R = \frac{\rho l}{A} = \frac{\rho a}{bl}$$

Power $$P = V^2/R = (BaV)^2 \frac{bl}{\rho a} = \frac{B^2V^2abl}{\rho}$$

Now i'm thinking that the power lost in the resistance of the mercury is equal to the kinetic energy lost by the mercury which flows per second. But i can't get to the final equation it wants.

Can anybody help?

Thank you