Thursday
February 11, 2016

# Homework Help: Physic ~ pls help

Posted by cr on Friday, April 15, 2011 at 11:10am.

A heavy conductor (mass m, length `, resistance R) is suspended by two springs each with spring constant k, and connected to a battery with electric potential V as shown in
the figure. A magnetic field ~B is now imposed. The acceleration of gravity is 9.8 m/s2 .
Which direction should the magnetic field point to have the most effect in raising the heavy conductor?
1. Out of the page
2. Into the page
3. Vertically downward in the plane of the page
4. The direction of the magnetic field is irrelevant.
5. To the left in parallel to the the conductor
6. Vertically upward in the plane of the page
7. In the plane of the page at a 45 degree angle to the conductor
8. To the right in parallel to the conductor

The key is the direction of the current, and the direction of B in relation to the conductor.
Still not sure here is the sketch...

---------- + - -------
| V |
| |
Spring K Spring K
| |
| |
<----------l--------->
Heavy Conductor R
|
mg