Exploring Magnets – Lecture Review

These flashcards cover definitions, principles, experiments, Earth’s magnetism, magnet-making methods, storage and care, and everyday applications discussed in the lecture.

What is a magnet?

An object that can attract iron and certain other materials due to the property of magnetism.

What is magnetism?

The property of a substance that enables it to exert an attractive or repulsive force on specific materials such as iron.

What is meant by magnetic force?

The force exerted by a magnet; it can act at a distance without direct contact.

Name three common magnetic materials.

Iron, nickel and cobalt.

Give three examples of non-magnetic materials.

Copper, wood and plastic (others include gold, silver or rubber).

Where are a magnet’s poles located?

At the ends of the magnet where the magnetic force is strongest.

What is the direction-finding property of a magnet?

A freely suspended magnet always comes to rest in the north-south direction.

Which pole of a magnet points toward the geographic North Pole?

The north-seeking pole, commonly called the north pole of the magnet.

What happens if you cut a magnet into two pieces?

Each piece becomes a complete magnet with its own north and south poles.

Can isolated north or south poles exist?

No; magnetic poles always exist in pairs.

State the law of magnetic poles.

Like poles repel each other, and unlike poles attract each other.

What is the sure test for magnetism?

Repulsion—if a body is repelled by a known pole, the body is definitely a magnet.

Describe the single-touch method for making a magnet.

Stroke an iron bar or needle 30-40 times in one direction with one pole of a bar magnet, lifting it away after each stroke; the stroked end becomes the same pole as the stroking pole.

How are most modern magnets manufactured?

By using electric current (electromagnetic methods) rather than manual stroking.

How should bar magnets be stored to prevent self-demagnetization?

In opposite pairs with a wooden spacer and soft-iron keepers placed across their ends.

List two actions that can weaken or destroy a magnet.

Heating a magnet or dropping/hammering it.

Why does a freely suspended magnet align north-south?

Because Earth behaves like a giant bar magnet whose magnetic south pole is near the geographic North Pole and vice versa.

Where are the Earth’s magnetic poles located relative to its geographic poles?

Earth’s magnetic south pole lies near the geographic North Pole, and the magnetic north pole lies near the geographic South Pole.

Name three typical shapes of artificial magnets.

Bar magnet, horseshoe (U-shaped) magnet and ring magnet.

What is a magnetic compass and how does it work?

A device with a magnetized needle pivoted in a non-magnetic case; the needle aligns itself north-south, allowing direction finding.

How can you check if an unfamiliar metal bar is a magnet?

Bring a known north pole near both ends; if one end is repelled and the other attracted, the bar is a magnet.

What determines how far a magnet’s influence extends?

The strength of the magnet and the distance from it; stronger magnets create larger regions of influence.

Does magnetic force act through non-magnetic materials like plastic or cardboard?

Yes; such materials do not block magnetic force.

Give four everyday uses of magnets.

Direction finding in compasses, electric motors, refrigerator door closures, and data storage in credit/ATM card magnetic strips (also dynamos, speakers, hard disks, etc.).

What is lodestone?

A naturally occurring rock made of magnetite that is naturally magnetized and can attract iron.