Electromagnetism
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Are magnetic forces contact or non-contact?
Non-contact
What is a magnet?
An object capable of exerting a magnetic force.
What is the difference between a permanent and an induced magnet?
Permanent is always magnetic whilst induced only becomes a magnet when it’s in a magnetic field. Induced can only attract.
Describe magnetic field lines?
They point from the North Pole to the South Pole and don’t cross each other. It is strongest where they are closest.
What is the Earth’s magnetic field caused by?
The iron and nickel core.
What is a magnetic field?
Area surrounding a magnet that can exert a force on magnetic materials.
What is a solenoid?
A coil of wire carrying an electrical current - its shape causes a stronger magnetic field.
What does an electromagnet consist of? What is an example of where they are used?
A solenoid with an iron core. An electric door bell.
What is Flemings left hand rule used for?
To find the direction of a force on a conductor in a magnetic field.
Fleming’s left hand rule: Thumb Forefinger Second finger
Thumb - movement Forefinger - field Second finger - current
What is a dc motor?
An electrical device that uses direct current to produce a turning effect.
What is a split ring commutator’s purpose?
To keep the motor rotating in the same direction by allowing the current in the coil to change direction each half-turn as the coil rotates.
What will increase the strength of the magnetic field around a wire carrying a current?
Increasing the current.
What is the effect of putting an iron core inside a solenoid?
The electromagnet becomes stronger.
What are poles?
Ends of a magnet where the magnetic forces are strongest.
Describe how a material becomes a magnet?
When a magnetic material is placed in a magnetic field, a magnetic field is induced and the material becomes a temporary magnet. When the material is removed from the magnetic fields the induced magnet loses all its magnetism.
List some magnetic materials.
Iron Cobalt Nickel Steel
How can it be shown that a magnetic material is a permanent magnet?
It will attract and repel another magnet.
What do the strengths and directions of magnetic fields depend on?
Strength - distance from the magnet Direction - the direction of the force that would act on another north pole places at that point
Describe how to plot the field line pattern of a bar magnet.
• Place the compass near the n pole of the magnet 2.. Mark a small cross where the compass needle is pointing • Move the compass so the South Pole of the needle touches this cross • Repeat this until the South Pole if the magnet is reached • Join the crosses to show the field lines • Repeat for different positions from the n pole of the magnet
Electromagnetism
The effect where a magnetic field is produced by result of an electric current flowing through a wire.
Current flows from … to …
Positive to negative
Magnetic field is directly proportional to … It is inversely proportional to …
Current in the wire Distance from the wire
Describe the right hand grip rule for a wire.
Thumb points in the direction of the current Fingers point in the direction of the field