Physics - Magnetism

What is the definition of a magnetic field?

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

What are permanent magnets?

Produce own magnetic field; repel and attract other magnets; made from a magnetic material; cannot be demagnetised.

What are magnetic materials?

Becomes a magnet when it is placed in a magnetic field; when removed from the magnetic field, it loses its magnetism.

How do magnets interact with other magnets and magnetic substances/materials?

Magnets repel and attract other magnets; they attract (but not repel) magnetic substances/material.

What is the significance of magnetic field lines?

Used to represent the strength and direction of a magnetic field; arrows show direction.

How is the strength of a magnetic field shown?

By the spacing of the magnetic field lines: close together = strong; far apart = weak.

Where is the magnetic field strongest around a magnet?

At the poles, where the magnetic field lines are closest together.

What happens to magnetic field strength as distance increases?

It becomes weaker; magnetic field lines get further apart.

What happens when magnetic materials are placed in a magnetic field?

Magnetism is induced; atoms line up; material is pulled toward the magnet.

Name materials that are non-magnetic and cannot be magnetised.

Aluminium, copper, brass, lead, gold, and silver.

Describe the properties of magnetically hard materials.

Make permanent magnets; hard to magnetise and demagnetise; e.g., steel (alloys of iron, nickel, cobalt).

Describe the properties of magnetically soft materials.

Easily magnetised and demagnetised; good for electromagnets; e.g., iron.

How can you investigate the shape of magnetic field pattern for a bar magnet?

Place magnet under paper/plastic; sprinkle iron filings; tap gently;

How do you produce a uniform magnetic field pattern using two bar magnets?

Place opposite poles of two bar magnets close; field lines move from north to south; lines are straight, parallel, evenly spaced.

What is the Right Hand Grip Rule?

Thumb = current; curled fingers = field direction; in solenoid: fingers = current, thumb = field direction (points to N pole).

How is an electromagnet constructed?

Wrap insulated wire into a coil around a soft iron core; connect wire to an electrical source and pass a current through

How can you make an electromagnet stronger?

Increase current, increase coil turns, add soft iron core, use solenoid with larger cross-section.

What are advantages of electromagnets?

Can be turned on/off, control strength (by current), change N/S poles (by reversing current).

What is Fleming’s Left Hand Rule?

First finger = field (N to S), second finger = current (+ to -), thumb = thrust (force).

How does the force on a current-carrying conductor change with the field/current?

If current or field direction is reversed, force reverses; if magnitude increases, force increases.

What are the three things that a magnetic field shows?

The strength, direction, and shape of the magnetic field.

explain the domain theory

Step 1:

Magnetic materials contain microscopic regions called domains, where atomic magnetic moments are aligned in the same direction.

 

Step 2:

In an unmagnetised material, domains are oriented randomly, causing their magnetic effects to cancel out.

 

Step 3:

When exposed to an external magnetic field, the domains align and the material develops a net magnetic field and becomes magnetised.

 

Step 4:

When the external field is removed:

• In soft magnetic materials, domains return to random orientations (demagnetised).

• In hard magnetic materials, domains remain aligned, retaining permanent magnetisation.

how cna you invesatigate the shape and direction of a magentci field

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

what is a solenoid

a wire that is wound in a cylindrical shape

what is an electromagnet

a wire (solenoid shape) with a current passing through, normally wrapped around a soft iron core