You are Here: Home >< Physics

# Electromagnetic induction ... watch

1. Can anyone tell how we will find out the induced direction of current in this question?
Attached Images

2. according to lenzes law the current produced opposes the motion causing it os the top side will aquire a polarity siilar to the polarity of the apraoching pole use your right hand pointing your thum towards north and curver your fingers to find the direction of current
3. Ah got it now thanks .... the corck screw rule.

I was trying to find this out by consedering the motion of the magnet , and than applying the fleming rules ... lol.
4. I gota get my head into transformers it's weird that you find everybody got something tricking their heads up
5. So what's the answer? I don't understand what they mean by an induced magnetic polarity
6. meh ... transformers is easy .. most of the course is easy it's just that the way that the question are set out that makes your forget whatever you might know!

I don't think that there've been any dodgy questions on transformers , just remember that voltage is induced due to flux linkage/induced emf blah blah.
7. (Original post by endeavour)
So what's the answer? I don't understand what they mean by an induced magnetic polarity
Lenz law - Any current driven by an induced emf opposes the change causing it. When the magnet approaches the top of the coil a current is induced in the coil. This current flow opposes the change that causes it - the movement of the magnet. So the coil repels the magnet and its top becomes a north pole. This gives a current which flows to the left on the top wire or downwards through the data logger
8. (Original post by endeavour)
So what's the answer? I don't understand what they mean by an induced magnetic polarity
you know from faradays law the change in magnetic flux cause an induction of emf which produces a current according to lenz's law that will oppose the motion,now you come to think how will it oppose the notion you know that current has a magnetic field so the current flows in a way that will make the top part of the coil (north posle) to repel the north pole that is approaching.
now by using right hand rule you let your thum points toewards the north pole your fingers will cureve to show the direction of the current like those fingertips will go saying (yo man the current is coming waaaatch out) ok silly I know
9. (Original post by Economist)
Lenz law - Any current driven by an induced emf opposes the change causing it. When the magnet approaches the top of the coil a current is induced in the coil. This current flow opposes the change that causes it - the movement of the magnet. So the coil repels the magnet and its top becomes a north pole. This gives a current which flows to the left on the top wire or downwards through the data logger
(Original post by habosh)
you know from faradays law the change in magnetic flux cause an induction of emf which produces a current according to lenz's law that will oppose the motion,now you come to think how will it oppose the notion you know that current has a magnetic field so the current flows in a way that will make the top part of the coil (north posle) to repel the north pole that is approaching.
now by using right hand rule you let your thum points toewards the north pole your fingers will cureve to show the direction of the current like those fingertips will go saying (yo man the current is coming waaaatch out) ok silly I know
OOh thanks a lot. So because the top of the coil is north, you kinda do the right hand grip thing (where you give a thumbs up) with the thumb pointing upwards) which then means the current is going from the bottom to the top of the coil (anticlockwise of the whole circuit).
10. Im assuming here the issue is with the current direction.

The important thing is the current will act so as to oppose the motion at ALL times due to Lenz's law. Therefore the current will flip during the motion.

To start with the coil will act as a north pole to repel the magnet. Therefore using right hand grip rule the curent will be anticlockwise initially. However, as soon the magnet passes through the centre it will become a south pole at the top and a north at the bottom. So that when the magnet leaves the coil will act to attract the magnet and so pull it back (opposing its motion.) Therefore at this point the current will be clockwise.
11. ok the theory has been said... so lets get to the point: The answer if its anti clockwise (North thing) then the current would act LEFT?
12. (Original post by LT0918)
ok the theory has been said... so lets get to the point: The answer if its anti clockwise (North thing) then the current would act LEFT?
well it goes anti-clockwise around the whole loop. So left at the top and right at the bottom.
13. That makes sense, thanks =)
14. how do u ue the right hand grip rule for all this north pole south pole business...i jst thort it was for the field aorund a wire??
15. (Original post by mackin boi)
how do u ue the right hand grip rule for all this north pole south pole business...i jst thort it was for the field aorund a wire??
they work off each other. Current goes around field and field goes around current. So your thumb is the direction of the field and your fingers is the direction of the current flow.
16. Theres another method (although similar) to determine the direction of the current from the polarity of the poles (or vice versa).

If the top of the coil is the south pole, you draw the letter S in the center of the coil, and if you drew arrows on the ends of the S, the arrows would point in a clockwise circle, which would be the direction of current in the coil.

If the top of the coil is a north (which it is), you draw an N (but with curved ends), with arrows on the ends, which point anticlockwise, meaning the current is driven anticlockwise.

I'm not sure that made sense
17. (Original post by Migraine)
Theres another method (although similar) to determine the direction of the current from the polarity of the poles (or vice versa).

If the top of the coil is the south pole, you draw the letter S in the center of the coil, and if you drew arrows on the ends of the S, the arrows would point in a clockwise circle, which would be the direction of current in the coil.

If the top of the coil is a north (which it is), you draw an N (but with curved ends), with arrows on the ends, which point anticlockwise, meaning the current is driven anticlockwise.

I'm not sure that made sense
Drawn it
Attached Images

18. N pole induced on the top of the wire [lenz's law]

right hand grip rule to show current going a/c/w.

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: June 15, 2005
The home of Results and Clearing

### 3,163

people online now

### 1,567,000

students helped last year
Today on TSR

### University open days

1. Sheffield Hallam University
Tue, 21 Aug '18
2. Bournemouth University
Wed, 22 Aug '18
3. University of Buckingham