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## Physics library

### Course: Physics library>Unit 13

Lesson 4: Magnetic flux and Faraday's law

How a current can be induced in a loop of wire by a change in magnetic flux.

## Want to join the conversation?

• How do we know the direction of the induced current?
• You can use Fleming's Right Hand Rule, for which you only need your right hand (surprise!):
- point your thumb toward the motion of the conductor
- point your first finger in the direction of the magnetic field
- and then if you make a 90-degree angle between your first and second finger, then your second finger points in the direction of the induced current.

Edit:
It is a bit strange to explain so I am adding a link for a picture of the Right Hand Rule
https://en.wikipedia.org/wiki/Fleming%27s_right-hand_rule#/media/File:RightHandOutline.png
• Why is the current going in the clockwise direction? According to the right hand grab rule, if I grab the right side of the wire, my index fingers point out, which means my thumb points up! How confusing! Thanks for your answer.
• So according to the right hand rule, the current would technically be running in a counterclockwise direction. However, if you think about what would happen if the current were to run in this direction, you will find that an increase in the current would further increase the magnetic field, which would in turn increase the current and create an unending increase in these variables. This is why the induced current due to flux always runs in an opposite direction than that of the right hand rule. Hope that makes sense. See the next video, "Lenz's Law" for further clarification.
• Alright so a change of magnetif flux induces current. But why??
• Magnetic flux comes from a magnetic with positive and negative charge. Current is the flow of (negatively charged) electrons. A movement in the magnet, and thus change in magnetic flux, will force electrons to move in a coil and therefore induce a current
• At , when Sal said the bigger velocity arrows would be on the right side of the field, why is that? Wouldn't the bigger vector lines be on the left side since that is where the field is stronger (the field lines are more dense here)?
• I think you are correct. Was a little confused myself at that point in the video.
• Why is a current induced when there is a change in magnetic flux? What is the mechanism exactly?
• Charges experience a force in the presence of a changing magnetic field.
Asking why is like asking why do like charges repel and unlike charges attract. These are fundamental features of our universe and we don't have a deeper explanation of why those features are what they are.
• How does electromagnetic strength (e.g. number of magnets) affect the induced current peak maximum?
• The larger the field strength (ie. more magnets) or the faster the cross sectional area is changing for the current loop, then the larger the induced EMF which creates a larger current.
• if i move the loop wire in a uniformly distributed magnetic field, would there be any induced current?
• Hello Minh,

No. As far as the loop is concerned there is no change in magnetic flux consequentially there will be no induced current.

However, if you rotate the loop the magnetic field would change. This is the principle behind motors and generators...

Regards,

APD
(1 vote)
• At , does it always go clockwise?