If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

### Course: Physics archive>Unit 10

Lesson 5: Discovery of electromagnetism

# Electromagnetic field (loop)

Applying current in various directions to a single loop of wire. Primitive electric motor? Created by Brit Cruise.

## Want to join the conversation?

• This time (compared to the previous video in this playlist) the wire is placed both above and below our compass. What's the effect of this on the observed motion?
• As he showed in the last video when you hold the wire above the compass, you see clockwise motion. When you hold the wire below, you see counterclockwise motion.
Thats the reason for the tapping on the battery poles. If he didn't there would be no motion because there is both clockwise and counterclockwise drag. (which would hold the needle in the most "relaxed" position.
• So, "in various directions" means touching the battery poles at different spots? The relative position of the two spots has something to do with the motion of the needle?
• If you watch the Brit's hands, on the battery; then you'll see he switched his electrode orientation. He changed the direction of the current in the wire. He tried to demonstrate that his can change the direction of needle deflection and the direction of needle spin. This kind of reversal may allow a toy car to move forward or reverse, without changing batteries. By changing contact orientation, a wheel may spin a different direction.
• That reminds me of how a hard drive works, what kind of motor would that be called?
• I agree that this is the basis for a DC motor, I also think that on an oscilloscope this would show as a square wave. With that in mind what kind of DC motor would this be?
• What's going on in this video?
• He is using a compass that uses the magnetic fields of the earth, and then connecting the compass to a battery which plays with the magnetic field around the compass
• Why does the needle change directions when you switch the clips on the end of the wire from negative to positive?
• because of change in the flow electricity as well as change of terminals like before it was positive then he changes it to negative that is why the needle moved in opposite direction.
• In the blue print, it mentions an electric motor. What is that and what does it do? Somebody please answer this.
• Does connecting a compass to a battery hurt the compass in any way?
Thanks!
(1 vote)
• No because the compass should eventually return to it's own electromagnetic field after you have "interfered" with it. Please correct me if I am wrong.