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### Course: Bridge Course Class 12th Physics>Unit 3

Lesson 1: Magnetism - I

# Magnetic field lines (& their properties)

Let's explore what magnetic field lines are, why we draw them, and what their properties are.

Here is the link to the simulation

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Created by Mahesh Shenoy.

## Want to join the conversation?

• Will there be a point wherein the magnet is broken up so many times and into such little pieces that it won't create a magnetic field?
• A couple of different things can happen when you cut a magnet. If you do it gently you can end up with two magnets. You can think of a magnet as a bundle of tiny magnets, called magnetic domains, that are jammed together. Each one reinforces the magnetic fields of the others. Each one has a tiny north and south pole. If you cut one in half, the newly cut faces will become the new north or south poles of the smaller pieces. Remember, I did say though you only get two magnets if you cut them gently. The magnetic domains in a magnetic material can be knocked loose, by bumping or vibrating the magnet (like when sawing it in half). If knocked loose, the domains are no longer arranged neatly, so they do not reinforce each other. If they are in a random orientation, with their fields pointing all over the place, they cancel each other out.
• when we break 2 magnets, it creates it own north and south pole so why does the south pole of the needle attracts the north pole of the magnet and vice versa
• All north poles attract all south poles and vice versa. The south pole of a magnetised needle attracts all north poles in the world, including it's own. It just isn't a spongy material so it can't bend to make the poles meet.
(1 vote)
• A magnetic compass when kept within the magnetic field always shows the direction,
but why are the fields considered as lines(closed loops), if the magnetic property can be detected anywhere within the magnetic field?
Shouldn't the force be like a 'cloud'( I know it's not the best choice of word but it's easier to imagine)?
• I guess there is a mathematical aspect to it. The cloud could provide us the magnitude of force at any point but we won't get its direction, whereas the tangent to the curve at any point would provide us the direction. But it would be nice to have both lines and cloud gradient to get both direction and magnitude of the magnetic field though we can get the magnitude on the basis of the density of field lines near the point of interest.
(1 vote)
• Why does a compass needle get deflected when brought near a bar magnet?
• Compass needles are sensitive to any magnetic field, not just the Earth's. Hope that explains.
• If we cut the bar magnet into squares, which side would be the north and south pole?

Considering that, how do we know that the ends of the magnet when kept vertically has 2 poles at the vertical ends and not the horizontal sides?

Shouldn't the horizontal sides also have north and south poles as a magnet consists of zillions of tiny magnets?

I know the questions may seem silly but it would be awesome if you could clear my doubt.
• Given that the magnetic field lines go straight through the magnet, I guess the new north and south poles would also follow them.
And some magnets in nature probably have poles along the horizontal sides, but the ones made for commercial use have been shaped to fit the normal shape of a bar magnet.
(1 vote)
• In the figure which appears at around , there is a field line which appears to be straight. Does that really happen and if yes, then a closed loop won't be formed?
(1 vote)
• That's a nice question. According to me, that straight field line is a closed loop. That's because we know that 2 parallel lines intersect at infinity. Likewise, the loop is closed at infinity.
• But what exactly are magnetic fields, I mean that we know that the stuff around us are made of atoms so we know what exactly are they, we exactly know what sound is, so upto that extent and in that sense, what exactly are fields?
(1 vote)
• Fields...or a Magnetic Field, particularly, is said to be the Space in which the Effect of The Magnet is Present or can be Felt. We Can Calculate How much a Magnetic Filed can Stretch By Conducting Experiments of How Strong the Magnet is, And How Far from the Magnet does it's Strenght Effect Objects. :)
• if 2 magnets are kept near each other and the magnetic field lines supposedly intersect and u keep a compass on that intersection, wouldn't the compass just point towards the stronger magnetic field instead?
(1 vote)
• Hey, @ Joseph Mathew Joy that is a really good question. But in the first place: Magnetic field lines never intersect at all.No matter how much you try. In the second place though dear friend, influence keeps the compass pointer deflected and not point in the direction of a stronger field.
What do I mean by influence? A compass would feel slight deflection even when placed far away from the magnet.(Correct me if I am wrong). This happens with a single magnet. Therefore imagine the deflection variation when two of them are kept.

So hence it won't point towards one direction rather it would be towards the middle of the two in a way wherein we can't predict/accurately say which direction is it pointing to.

Let me know if this helps. Sorry for the long explanation.

Nolan R.T :)