magnetism

At which parts of a magnet is the magnetic forces most strongest

At the poles

what is 1mA equivalent to

0.001 Amps

What happens when two magnets are brung close to each other

They exert a force on each other

What force is exerted when two like poles are brought close

They repel

What force is exerted if two opposite poles are brought Close together

They attract

What is attraction and repulsion between 2 magnetic poles an example of

Non-contact force as magnets dont have to touch to experience a force

What is a permanent magnet

A magnet that produces its own magnetic field

WHAT IS AN INDUCED MAGNET

A material that has to be put inside a magnetic field to become magnetic

How to reverse direction of force extorted on wire

• reverse direction of current flowing in coil

• Wrap wire around coil in reverse direction

• Reverse placing of magnets (north and south)

How to make an electromagnet

1. Secure iron nail to clamp vertically

2. Take insulated wire and wrap it around nail leaving 15-20cm free connection

3. Use connecting leads to connect ends of wire to power supply

4. Bring steel paperclip near nail (if attracted it works)

Safety precautions

• dont leave current on too long : wire overheat

• Use low voltage DC to avoid shocks

How to vary strength of electromagnetic

• increase number coil turns

• Increase current

Ho to test if electromagnetic works

• suspend steel paperclips near iron nail to test if attracts

• Add more paperclips to test the strength of magnetic field (more=stronger)

• Clamp electromagnetic from different distances from paperclips (further away it attracts magnet means the stronger it is)

• Test before and after changes so can compare strength

What type of force does induced magnets always cause

Force of attraction

What happens when an induced magnets is removed from magnetic field

Looses all/most of its magnetism

What is an magnetic field

The space around a magnetic field where there eis a non-contact force on a magnetic material

Give 4 examples of magnetic materials

1. Cobalt

2. Nickel

3. Steel

4. Iron

What is always said about a force between a magnet and a magnetic material

It is always attractive

What does the strength of a magnetic field depend on

How close the field lines are

If the field lines are closer, what does that tell you

The magnetic field is stronger

If the magnetic field is weaker, how can we tell

If the field lines are further apart

How does strength of a magnetic field change as you move further away from the magnet producing it

Decreases as you move further away

What direction do magnetic field point

North to south poles

What does a magnetic compass have

A small bar magnet that points in the direction of the earths magnetic field

What direction does compass point when not near a magnetic material and why

North as earth has an iron core which is magnetic

What is produced when current flows through a conducting wire?

A magnetic field is produced around the wire

What happens if you change direction of current

change the direction of the magnetic field

What does strength of a magnetic field depend on, name 3

1. Size of current

2. Distance from wire

3. How close the field lines are

How to make magnetc field stronger

• larger current flowing through wire

• Closer to wire/magnetic material

How to increase strength o magnetic field

1. Increase current

2. Move magnetic field closer to wire

What is a solenoid

A coil of wire which when current flows through, it creates a strong magnetic field inside solenoid

Describe the magnetic field found inside a solenoid

Strong and uniform

What is an electro-magnet

A solenoid (a coil of wire) with an added iron core

How to increase strength of magnetic field in a solenoid and electromagnet (Name three)

1. Increase turns in the wire

2. Add iron core

3. Increase current size

4. Decrease wire length

Why does adding an iron core increase magnetism

• iron is a soft magnetic material

• So it makes electro-magnetic an induced magnet

• So when current flows through the strength of magnetic field increases

Why are electro-magnets useful?

• Magnetism able to be turned on and off

• Can increase strength of magnetic field easily by increasing current so strength easily controlled

• Can be made very strong

Give 3 examples where electro magnets are used

1. Electric motors like fans and hairdryers

2. MRI scanners in hospitals

3. Cranes

4. Electric bell

What is the RIGHT hand thumb rule

• point thumb in direction of current

• Curl fingers in direction of magnetic field

How could u also increase strength of a magnetic field that a wire produces

Wrap a wire in a coil (make it a solenoid)

Why dos adding a solenoid increase magnetic field around wire

Field lines around loop of wire line up with each other so they are brung closer together

What is the motor effect?

When a force is exerted between a magnetic field and a current carrying wire or any conductor which causes the wire to move by being placed in a magnetic field

What happens in motor effect

• current carrying wire or any conductor is put inside a magnetic field

• Magnetic field around the wire interacts with magnetic field

• Which causes wire and magnet to exert a force on each other

• Which causes wire too move in direction force is exerted

When is force maximum and why

When wire is perpendicular (90 degrees) to magnetic field because wire is crossing maximum amount of field lines

what is evidence that warts core is magnetic with compass

• always points north

• so it aligns itself with earths magnetic field

When is force at zero and why

When wire is parallel to magnetic field as its not crossing field lines

What role is used to determine the force exerted due to motor effect

Flemmings LEFT hand rule

Explain Flemmings left hand rule- what does thuMb represent

MOTION- direction of force

Flemmings left hand rule- what does second finger represent

Direction current is flowing

Flemmings left hand rule- what does First Finger represent

Direction of Field (north to south poles)

What do dots represent in diagrams

Current is coming out so point finger out

What do crosses represent in a diagram

Current going in so point fingers into page

Which way do fingers have to point?

North to south

What is the equation and what does each part stand for

F= BIL

What does the F stand for in the equation

Force on the wire, measured in newtons

What does B stand for in equation

Magnetic flux density, measured in tesla

What does I stand for in equation

Amount of current flowing in wire, measured in AMPS

WHAT DOES L STAND FOR EQUATION

Length of wire, measured in metres

Which way does current always flow

From positive (+) to negative (-)

What factors affect size of force on a current carrying wire in a magnetic field

• magnitude of current flowing through conductor

• The strength of magnetic field that conductor or current carrying wire is placed in

What affects size of force on a current carrying wire in a magnetic field

• magnitude of current flowing through wire

• Strength of magnetic field the wire is placed in

If the strength of current carrying wire placed in a uniform magnetic field is increased, what happens to force

Strength of force increases

What do electric motors do

Convert electric energy into mechanical energy to produce momentum

What is momentum

A turning effect

What are electric motors powered by

DC- direct current

What is direct current produced by

Batteries and cells

What does basic dc motor do

Allows force to act on two arms of coil of wire that carry current

Explain the process of electric motors

1. Will be a magnetic field between two bar magnets

2. A conducting wire will be placed between poles connected to circuit

3. When electric current flows through coil, the coil experiences a force and move

1. The opposite forces on each side attract and causes loop of wire to rotate (creating momentum)

2. A split ring commutator is needed to keep coil spinning

3. When commutator revered, direction of current is reversed in each side

4. This means force on left side is always upwards due to its own momentum

5. When coil is vertical there is no current as no connection to battery so no force on coil

6. But coil continues to turn as force on right is always downwards

What does split ring commutator do

Reverses current in coil for every half turn to keep coil spinning

When coil has spun quarter turn from horizontal, there is no force why

Split ring commutator has no connection to battery so there will be no current flowing through wire so no force

When wire has reached 90 degrees and is vertical what happens

The wire will stop rotating

If wire continues to rotate beyond 90 degrees without a split ring commutator what happens

The force direction on left will move downwards and on right hand side it will move upwards pushing it back ti vertical position in which it stops. (Opposite directions)

How do fix when wire stops rotating

Reverse current (add split ring commutator)

What Is split ring commutator connected to and why

Metal conducting brushes as it allows current to pass into ring

why is a direct current induced into coil

• as coil will move through magnetic field

• so potential difference will be induced in coil

• which forms a complete circuit so current is induced in the coil

• so each half-revolution the two halves of commutator switches brushes so direction of current is not reversed every half rotation

explain how an electromagnet becomes magnetic

• when circuit is completed current flows turning it on

• so when coil of wire has current flowing through exerts equal but opposite force onto magnetic field

• so magnetic field produced around coil

• so iron core (which has wire wrapped around) becomes magnetic

explain how a permanent magnet effects aluminium, iron and another permanent magnet

• won’t have an effect on aluminium

• pm attracts iron

• permanent magnet can repel permanent magnet

I ihow to increase the force exerted by an electromagnet

2. By y increasing the current I

By y bring magnet closer to material

when wire is placed inside magnet what force exerted

• magnetic field is produced around the wire and is placed in a magnetic field

• So equal but opposite force is exerted in the wire that it exerts in the magnetic field

Why is there a force when current flows in wire

• because there will be a magnetic field around the wire

• And already a magnetic field due to the magnets as placed in between the poles so

• Interact exerting equal but opposite forces into each other

Which are the most powerfully magnets

Electro magnets as can vary strength and can turn magnetism in and off

What becomes magnetised in electromagnet

The iron core is becomes an magnet (induced)

Explain why when a current is in a coil it rotates

• this produces a magnetic field around the wire which is already in a magnetic field

• So they interact

• Current is flowing in opposite directions in either side of coil (positive and negative)

• Forces are acting in opposite directions in either side of coil

• So on left there is downwards force and in right it is upwards

• Causing wire to turn

• Split ring commutator needed to reverse direction of the current for every half turn so force in either side remain acting in same direction