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Interactions of two bar magnets placed side by side

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Interactions of two bar magnets placed side by side

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Like poles of two bar magnets repel each other.

Point x in Figure 19.25(a) is called a neutral point, because the resultant magnetic field in that region is zero.

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Unlike poles of two bar magnets attract each other.

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Magnetic field lines are directed outwards from the North pole towards the South pole.

Magnetic field lines do not cross or intersect one another.

The distance between the magnetic field lines represents the strength of the magnetic field. The closer the lines, the stronger the magnetic field.

Since magnets are stronger at the poles, these field lines are more concentrated at the poles, as shown in Figure 19.19.

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Steps

1. place the plotting compass near the magnet on a piece of paper

2. mark the direction the compass needle points

3. move the plotting compass to many different positions in the magnetic field, marking the needle direction each time

4. join the points to show the field lines

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Differences between Soft and Hard Magnetic Materials

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Differences between Soft and Hard Magnetic Materials

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Soft magnetic materials (iron) have stronger induced magnetism compared to hard magnetic materials (steel).

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Temporary magnets are magnets that retain their magnetism in the presence of an electric current or a permanent magnetic field.

Permanent magnets do not require the presence of an electric current or a permanent magnetic field to retain their magnetism.

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1. Hitting or heating

2. Electrical method

using a solenoid with an alternating current that changes direction all the time. The magnetic field of the solenoid produced by passing alternating current will change direction every time the current changes direction.

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(a)   The paper clips are magnetised by induced magnetism. This process does not require physical contact between the magnet and the magnetic material. The magnetic material only needs to be near the magnet.

(b) The paper clips have become induced magnets. The bottom tips of the paper clips are like poles (North poles) and thus they repel each other.

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In an experiment, a piece of wood is held between the N pole of a bar magnet and two paper clips.

(a) Although wood is a non-magnetic material, the two paper clips are attracted when the wood is held between the magnet and the paper clips. Suggest a reason for this.

(b) It is observed that the bottom tips of the paper clips point away from each other. Why is this so?

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Magnetic field is a region in which the force of magnetism acts. 

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Magnetic field is a region in which the force of magnetism acts. 

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There are two ways to show the magnetic field pattern of a magnet.

1. Sprinkling iron filings around a magnet

2. Plotting the magnetic field pattern with a compass

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A current-carrying solenoid produces a magnetic field similar to that of a bar magnet, as shown in Figure 19.10.

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Magnetic induction is the process whereby an object made of a magnetic material becomes a magnet when it is near or in contact with a magnet.

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Magnets are made up of atoms. At the subatomic level, electrons circulate around the atomic nuclei and spin about their own axes.

This electron spin give rise to an atomic magnet i.e. a tiny magnet of subatomic dimensions.

The magnetic domain theory states that there are regions called domains in which the atomic magnets are aligned, as shown in Figure 19.6.

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The only test for magnetism is repulsion between two magnets.

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1. Like poles repel and unlike poles attract.

2. Magnets have two poles. The magnetic field strength is strongest at the poles.

3. Magnets attract magnetic materials (e.g. iron, nickel, cobalt, steel).

4. A freely suspended magnet comes to rest in the North−South direction.

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Please ask any questions you have on this topic...

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Please ask any questions you have on this topic...

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describe how a bar magnet (e.g. a compass) can be used to determine the direction of a magnetic field

draw the magnetic field pattern around a bar magnet and between the poles of two bar magnets.

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Interactions Between Magnets and Magnetic Materials

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Interactions Between Magnets and Magnetic Materials

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state the properties of magnets

describe induced magnetism caused by placing magnetic material close to a strong magnet or within a current-carrying solenoid

distinguish between temporary magnets (e.g. iron) and permanent magnets (e.g. steel) in terms of their properties and uses