Define magnetic material .

A magnetic material is a substance that experiences a force when placed in a magnetic field and can be magnetised , for example iron, steel, cobalt and nickel.

Define the law of magnetism .

Like poles repel each other; unlike poles attract each other.

How can you test whether an object is a genuine magnet , rather than just a magnetic material?

Bring it close to a known magnet. Only a genuine magnet can repel it; a magnetic material can only ever be attracted .

Magnetic materials always experience a force in a magnetic field and are ______ to a magnet when unmagnetised.

Magnetic materials always experience a force in a magnetic field and are attracted to a magnet when unmagnetised.

True or False? A non-magnetic material experiences a force when placed in a magnetic field.

False. Non-magnetic materials experience no force when placed in a magnetic field.

Define permanent magnet .

A magnet, usually made from steel , that produces its own magnetic field and does not lose its magnetism.

Give two uses of permanent magnets .

Any two from: compasses , school lab experiments , toys (e.g. joining train carriages), fridge magnets .

Why is soft iron , rather than steel, normally used as the core of an electromagnet?

Soft iron can be magnetised and demagnetised easily , so the electromagnet can be switched on and off, whereas steel would stay magnetised.

Give two uses of electromagnets .

Any two from: MRI scanners , speakers and earphones , recycling (separating steel from other materials), Mag-Lev trains .

Define permanent magnet .

A magnet made from a permanently magnetic material (e.g. steel ) that produces its own magnetic field and does not lose its magnetism.

Define induced magnet .

A magnetic material that becomes a magnet temporarily when placed in a magnetic field, and loses its magnetism when removed from the field.

Name three magnetic materials.

Any three from: iron , cobalt , nickel (steel is also magnetic, as it is an alloy of iron).

A permanent magnet is held near an unmagnetised piece of steel. What pole is induced at the end nearest the magnet, and why?

The opposite pole to the one nearest it, because magnetic materials are always attracted to a permanent magnet, never repelled.

Steel objects such as paperclips or needles remain ______ for a while after being removed from a magnetic field, whereas iron objects lose their magnetism almost immediately.

Steel objects such as paperclips or needles remain magnetised for a while after being removed from a magnetic field, whereas iron objects lose their magnetism almost immediately.

True or False? Induced magnetism disappears immediately in every magnetic material once it is removed from the field.

False. Steel objects (e.g. paperclips, needles) remain magnetised for a while; only soft iron objects lose their magnetism almost immediately.

In a worked example, a suspended piece of metal is attracted towards pole X of a magnet. What can you conclude about pole X and the metal?

Pole X must be a north pole , since the metal is attracted rather than repelled (unlike poles attract). The metal must be a magnetic material (e.g. nickel), since only magnetic materials and magnets are affected by a magnetic field.

Define magnetic field .

The region around a magnet where a force acts on another magnet or on a magnetic material (such as iron, steel, cobalt or nickel).

Define a uniform magnetic field .

A magnetic field that has the same strength and direction at every point, shown by field lines that are equally spaced and parallel.

How is a uniform magnetic field produced using two bar magnets?

By placing opposite poles a few centimetres apart; a uniform field forms in the gap between them.

What two rules must magnetic field lines follow when drawn?

They must point from north to south (shown by an arrow), and they must never touch or cross another field line.

True or False? Outside the gap between two opposite poles held close together, the magnetic field is still uniform.

False. Outside the gap, the field is not uniform ; only the field directly between the opposite poles is uniform.

Where is a bar magnet's magnetic field strongest, and how is this shown on a field diagram?

It is strongest at the poles , shown by the field lines being closest together there.

The strength of a magnetic field is shown by the spacing of the field lines: if the lines are close together the field is ______ , and if they are far apart the field is weak.

The strength of a magnetic field is shown by the spacing of the field lines: if the lines are close together the field is strong , and if they are far apart the field is weak.

Describe how iron filings are used to plot the magnetic field around a bar magnet.

Place a piece of paper over the magnet, sprinkle iron filings on top, then gently tap the paper so the filings settle along the field lines.

Describe how a plotting compass is used to plot a magnetic field line around a bar magnet.

Mark a dot at one end of the magnet, place the compass so its needle points to the dot, mark a new dot at the other end of the needle, then move the compass to the new dot and repeat. Join the dots with a smooth curve to give the field line.

When plotting a field line with a compass, what does the direction of the line correspond to?

The direction the plotting compass needle points at each position along the line.

How can several magnetic field lines be plotted for the same magnet using the compass method?

Repeat the dot-and-compass process starting from different points on the magnet to build up several field lines.

What is the first step of either the iron filings method or the plotting compass method?

Place the magnet under (or on top of) a piece of paper.

When using iron filings, the paper should be gently ______ to allow the filings to settle along the field lines.

When using iron filings, the paper should be gently tapped to allow the filings to settle along the field lines.

True or False? When plotting a field line with a compass, the line drawn points from the south pole to the north pole of the magnet.

False. Field lines are drawn, and point, from the north pole to the south pole of the magnet.

O LevelPhysicsCambridge (CIE)Flashcards4. Electricity & Magnetism4.1 Simple Magnetism & Magnetic Fields

4.1 Simple Magnetism & Magnetic Fields (Cambridge (CIE) O Level Physics): Flashcards

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Cards in this collection (30)

Define magnetic material.
A magnetic material is a substance that experiences a force when placed in a magnetic field and can be magnetised, for example iron, steel, cobalt and nickel.
Define the law of magnetism.
Like poles repel each other; unlike poles attract each other.
How can you test whether an object is a genuine magnet, rather than just a magnetic material?
Bring it close to a known magnet. Only a genuine magnet can repel it; a magnetic material can only ever be attracted.
Magnetic materials always experience a force in a magnetic field and are ______ to a magnet when unmagnetised.
Magnetic materials always experience a force in a magnetic field and are attracted to a magnet when unmagnetised.
True or False?
A non-magnetic material experiences a force when placed in a magnetic field.
False.
Non-magnetic materials experience no force when placed in a magnetic field.
Define permanent magnet.
A magnet, usually made from steel, that produces its own magnetic field and does not lose its magnetism.
Give two uses of permanent magnets.
Any two from: compasses, school lab experiments, toys (e.g. joining train carriages), fridge magnets.
Why is soft iron, rather than steel, normally used as the core of an electromagnet?
Soft iron can be magnetised and demagnetised easily, so the electromagnet can be switched on and off, whereas steel would stay magnetised.
Give two uses of electromagnets.
Any two from: MRI scanners, speakers and earphones, recycling (separating steel from other materials), Mag-Lev trains.
Define permanent magnet.
A magnet made from a permanently magnetic material (e.g. steel) that produces its own magnetic field and does not lose its magnetism.
Define induced magnet.
A magnetic material that becomes a magnet temporarily when placed in a magnetic field, and loses its magnetism when removed from the field.
Name three magnetic materials.
Any three from: iron, cobalt, nickel (steel is also magnetic, as it is an alloy of iron).
A permanent magnet is held near an unmagnetised piece of steel. What pole is induced at the end nearest the magnet, and why?
The opposite pole to the one nearest it, because magnetic materials are always attracted to a permanent magnet, never repelled.
Steel objects such as paperclips or needles remain ______ for a while after being removed from a magnetic field, whereas iron objects lose their magnetism almost immediately.
Steel objects such as paperclips or needles remain magnetised for a while after being removed from a magnetic field, whereas iron objects lose their magnetism almost immediately.
True or False?
Induced magnetism disappears immediately in every magnetic material once it is removed from the field.
False.
Steel objects (e.g. paperclips, needles) remain magnetised for a while; only soft iron objects lose their magnetism almost immediately.
In a worked example, a suspended piece of metal is attracted towards pole X of a magnet. What can you conclude about pole X and the metal?
Pole X must be a north pole, since the metal is attracted rather than repelled (unlike poles attract). The metal must be a magnetic material (e.g. nickel), since only magnetic materials and magnets are affected by a magnetic field.
Define magnetic field.
The region around a magnet where a force acts on another magnet or on a magnetic material (such as iron, steel, cobalt or nickel).
Define a uniform magnetic field.
A magnetic field that has the same strength and direction at every point, shown by field lines that are equally spaced and parallel.
How is a uniform magnetic field produced using two bar magnets?
By placing opposite poles a few centimetres apart; a uniform field forms in the gap between them.
What two rules must magnetic field lines follow when drawn?
They must point from north to south (shown by an arrow), and they must never touch or cross another field line.
True or False?
Outside the gap between two opposite poles held close together, the magnetic field is still uniform.
False.
Outside the gap, the field is not uniform; only the field directly between the opposite poles is uniform.
Where is a bar magnet's magnetic field strongest, and how is this shown on a field diagram?
It is strongest at the poles, shown by the field lines being closest together there.
The strength of a magnetic field is shown by the spacing of the field lines: if the lines are close together the field is ______, and if they are far apart the field is weak.
The strength of a magnetic field is shown by the spacing of the field lines: if the lines are close together the field is strong, and if they are far apart the field is weak.
Describe how iron filings are used to plot the magnetic field around a bar magnet.
Place a piece of paper over the magnet, sprinkle iron filings on top, then gently tap the paper so the filings settle along the field lines.
Describe how a plotting compass is used to plot a magnetic field line around a bar magnet.
Mark a dot at one end of the magnet, place the compass so its needle points to the dot, mark a new dot at the other end of the needle, then move the compass to the new dot and repeat. Join the dots with a smooth curve to give the field line.
When plotting a field line with a compass, what does the direction of the line correspond to?
The direction the plotting compass needle points at each position along the line.
How can several magnetic field lines be plotted for the same magnet using the compass method?
Repeat the dot-and-compass process starting from different points on the magnet to build up several field lines.
What is the first step of either the iron filings method or the plotting compass method?
Place the magnet under (or on top of) a piece of paper.
When using iron filings, the paper should be gently ______ to allow the filings to settle along the field lines.
When using iron filings, the paper should be gently tapped to allow the filings to settle along the field lines.
True or False?
When plotting a field line with a compass, the line drawn points from the south pole to the north pole of the magnet.
False.
Field lines are drawn, and point, from the north pole to the south pole of the magnet.

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