Magnetic FieldMagnetic Field Magnets have both a Magnets have both a

north pole and a south north pole and a south pole.pole.

The magnetic lines of The magnetic lines of force flow from pole to force flow from pole to pole as shown in the pole as shown in the sketch.sketch.

It is easy to feel the It is easy to feel the attraction or repulsion attraction or repulsion when one plays with when one plays with two magnets. two magnets.

ElectromagnetismElectromagnetism

A magnetic field is produced when an A magnetic field is produced when an electric current flows through a coil of electric current flows through a coil of wire. This is the basis of the wire. This is the basis of the electromagnet. electromagnet.

We can make an electromagnet We can make an electromagnet stronger by doing these things: stronger by doing these things:

wrapping the coil around an iron core wrapping the coil around an iron core adding more turns to the coil adding more turns to the coil increasing the current flowing through the coil. increasing the current flowing through the coil.

A Simple Electromagnet:A Simple Electromagnet:

Using electromagnets Many objects around you

contain electromagnets. They are found in electric motors and loudspeakers. Very large and powerful electromagnets are used as lifting magnets in scrap yards to pick up, then drop, old cars and other scrap iron and steel.

They are better than magnets because the magnetism can be turned off and on.

Electromagnet animation

http://www.bbc.co.uk/schools/ks3bitesize/science/physics/magnetism_4.shtml

Electric bells

Electric bells like the ones used in most schools also contain an electromagnet.

When the current flows through the circuit, the electromagnet makes a magnetic field.

The electromagnet attracts the springy metal arm.

The arm hits the gong, which makes a sound and the circuit is broken.

The electromagnet is turned off and the springy metal arm moves back.

The circuit is complete again.

Animation of electric bell

http://www.bbc.co.uk/schools/ks3bitesize/science/physics/magnetism_5.shtml

Gravitational FieldsGravitational Fields

All objects have a force that attracts them towards each other. This is called gravity. Even you attract other objects to you because of gravity. But you have too little mass for the force to be very strong. Gravity only becomes noticeable when there is a really massive object like a moon, planet or star.

Gravitational FieldGravitational Field The Earth has more mass than the Moon,

so the gravitational force is greater on the Earth than it is on the Moon.

The Earth's gravitational force pulls objects towards the centre of the Earth.

"Down" is towards the centre of the Earth, wherever you are on the planet

Gravitational FieldGravitational Field

Earth’s gravitational force makes the ball move down towards the centre of the Earth.

Sun’s gravitational force makes the Earth move in an orbit around the Sun.

Electric FieldsElectric Fields

An electric field shows us how electric charges behave around each other.

See what elec field looks like: http://www.colorado.edu/physics/2000/waves_particles/wavpart3.html

Electric FieldsElectric Fields

Positive and negative charges attract each other.

What do two positive charges do to each other?

Electric FieldsElectric Fields

Lightning discharges an excess of positive and negative charge within clouds, between clouds, or between clouds and the ground.

Extension:Extension:

Physics textbook:Physics textbook:

Read p78-79 – GravityRead p78-79 – Gravity

Try questions 4 & 5 on p81.Try questions 4 & 5 on p81.

Read p139/140 and try questions.Read p139/140 and try questions.

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