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## Class 10 Physics (India)

### Course: Class 10 Physics (India)>Unit 4

Lesson 4: Force on current carrying wire in magnetic field

# Force on a current carrying conductor in a magnetic field

Current carrying wires can push magnets. Can magnets push current carrying wires too? Let's find out. Created by Mahesh Shenoy.

## Want to join the conversation?

• But why does force depend on angle of wire ?
• Hey!
Before I try to answer your question(which is awesome!) I'd like to make a couple things clear-----My answer is just a logical approach configured by me and I'm in 10th grade (India) so it's not exactly technical but it helped me to understand why(more or less)---

Now, here's my approach
> Try actually drawing the diagram and incline the wire
> In addition draw the concentric circles as well(magnetic field in a wire)-abt 2 for every point on the wire which touches the magnetic field lines produced by the 2 poles(parallel)
(I know..fun ;))

What can we observe
(Try it out yourself and then check out the rest)

> We can observe that when the wire is perpendicular, the magnetic field produced by the wire is literally lying on the magnetic field/s produced by the poles
keeping in mind that this is actually in 3-Dimensions and not in 2-D we can conclude/imagine that all the points on the magnetic field of the wire would experience a force by the magnetic fields of the poles,

> now, if we incline it, the area of the interaction between the magnetic fields decreases(remember there are gaps/spaces between 2 field lines

that's it!

by 'wire' I meant current carrying wire/conductor and force exerted/experienced depends on the region of interaction of the magnetic fields.

Hope this helps,

P.S;again I'm stressing on the point that I'm not sure if this is like 'The explanation', this is just how I was able to reason this out,
hope this appealed to your imagination as well
Onward!
• If we pass a current passing wire in between two magnets which obviously have magnetic fields , don't the magnetic field of current carrying wire and magnets field collide . If not how does the image look like ?
• They Don't collide or interact. They just push on each other
• At , why do the magnetic field lines go from north to south instead of south to north as it happens in a bar magnet?
• At , how are the field lines almost parallel? We know that outside the magnet, the field lines are like semi-circles of sorts, are not equidistant and go from North to South. Why is it different in this case?
• They are in that way cause they want to go to the south pole and as the south pole of a bar magnet is below the magnet, they go that way but in this example, the south pole of another magnet is placed in front of another north pole so they go straight.
(1 vote)
• I have a doubt here
.why force doesn't increase with decrease of current
Let's take a setting

The B is in direction perpendicular to current flowing in a wire (current north and the external B west)
so shouldn't the force be in the same direction as the B?
For this particular force on conductor situation In my textbook ,the force's direction is from north to south pole of the horseshoe magnet.
" keep the things above in mind for now"

The wire(from our setting) has its own magnetic field which interacts with the external field applied on it
If the current will decrease, the field would be less stronger now and would lead to more domination by the external current causing it to feel more force. But instead, it feels lesser force.

I know that there is equal and opposite force but we didn't change the external field nor position of our wire to cause lesser force b/w them
.

Would someone bother to help me get out of this confusion
• At , you mentioned Newton's third law. As far as I know, Newton's third law is only applicable for forces, not for other stuffs. So is it valid to explain these magnetic stuffs using that?
(1 vote)
• Yes newtons third law is applicable for all type of forces, and even the current carrying wire is applying force on magnetic needle, so there should be equal and opposite rxn for applied force acc. to newtons third law.
• What is the difference between the Right Hand Thumb Rule and the Flemings Left Hand Rule, because I felt that to, find the direction of the current and the direction of the magnetic field in a straight current carrying conductor we use the Right Hand Thumb Rule but can't we use the Left Hand Rule to find the direction of the current and the direction of the magnetic field ? I didn't understood the relation between these two things .
(1 vote)
• Hey Abhiram!
The difference between the right-hand thumb rule & Fleming's left hand rule is that they are used for different purposes in different scenarios.

Right Hand Thumb Rule is used when we know the direction of current and wish to find out the direction of the magnetic field.

On the other hand, Left Hand Rule is used when we know the direction of current as well as magnetic field, and wish to find out the direction of the force exerted

As you are mentioning, we can also use the Left Hand rule to find out the direction of current/magnetic field, provided we know the direction of other two factors (Force & Current/Magnetic field). But we would rather use the right hand thumb rule to find it as we need to know the direction ofonly one of the two factors here(Current/Magnetic field).

Hope it helps. Feel free to comment if your doubt persists...Have fun learning :)
• I think you have drawn the direction of magnetic field wrongly AFTER THE TIME OF 1'32"
(1 vote)
• Isn't the magnetic field in closed loops? How does these just vanish?