Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A horizontal copper rod of mass and length lies east to west in a horizontal field of that points north. Take .
A wire with a current in a magnetic field feels a force , where is the angle between the wire and the field. It is largest () at right angles, and zero along the field. Fleming's left-hand rule: forefinger for the field, middle finger for the current, thumb for the force.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The weight. .
Step 2. The current. .
Step 3. The direction. Left hand: forefinger north (field), thumb up (force). The middle finger points east.
Answer: , flowing from west to east.
Check. , the weight.
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