A magnetic field points into the page. A straight conductor in it is moved to the left.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A magnetic field points into the page. A straight conductor in it is moved to the left.
- Use Fleming's right-hand rule to find the direction of the induced current.
- Check it with the left-hand rule: which way is the force on this current?
Need a reminder? The key ideaShow
A current is induced in a coil while the magnetic field through it changes: when a magnet and the coil move relative to each other. It is larger for faster motion, a stronger magnet and more turns; it reverses when the motion reverses, and it opposes the change (Lenz's law). Fleming's right-hand rule: thumb for the motion, forefinger for the field, middle finger for the induced current.
The worked solution
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. (a) Thumb to the left, forefinger into the page: the middle finger points down the page. The induced current flows down.
Step 2. (b) Left hand: forefinger into the page, middle finger down the page. The thumb points to the right.
Step 3. Lenz's law. The force is to the right, against the motion to the left. The induced current opposes the change.
Answer: (a) down the page. (b) to the right, opposite to the motion.
Check. If the force helped the motion, the conductor would speed up by itself and make energy from nothing.
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