Electromagnetism Flashcards
What is an electromagnetic induction?
If an electrical conductor cuts through magnetic field lines, an electrical potential different is induced across the ends of the conductor. If the wire is part of a complete circuit, a current is induced in the wire.
Happens when any conductor crosses through magnetic field lines.
When will the size of the induced potential difference decrease?
The speed of the movement increases
The strength of the magnetic field increases
The number of turns on the coil increases
The area of the coil is greater
What is a generator?
Contains coils of wires that spin in a magnetic field. A potential difference or voltage is created, or induced, across the ends of the wire when it crosses through the magnetic field lines.
If the conductor is part of a complete circuit, the induced potential difference makes an electric current pass around the circuit. This effect is called the generator effect.
Why does the ammeter pointer deflect when one end of the bar magnet is pushed into the coil (generator effect)?
The movement of the bar magnet causes an induced potential difference across the bar.
The induced potential difference causes a current, because the coil is part of a complete circuit.
What happens when you use a stronger magnet in a generator?
If a stronger magnet is used, both the induced potential difference and the current will be bigger.
What happens to the ammeter pointer if the bar magnet is withdrawn from the coil? (generator)
The ammeter pointer deflects in a different direction. This is because the induced potential difference acts in the opposite direction, so the induced current is in the opposite direction m
Talk about the direction of the induced current in a generator.
The direction of an induced current always opposes the original change that caused it.
What are permanent magnets made of?
Steel because magnetised steel does not lose its magnetism easily.
What materials can be magnetised and demagnetised easily?
Iron, steel, cobalt and nickel.
What is the region around a magnet called?
Magnetic field.
What happens to an object that enters another objects magnetic field?
Any other material placed in this space experiences a force caused by the first magnet.
What are magnetic field lines also called?
Lines of force. These lines are more concentrated at the poles than elsewhere because the field is strongest at the poles.
Where is the field strongest?
At the poles.
What is the direction of a line of force?
Always from the north pole of the magnet to its south pole.
What happens to a plotting compass place in a magnetic field?
Aligns itself along a magnetic field line, pointing in a direction away from the N-pole of the magnet and towards the magnet’s S-pole.
What is induced magnetism?
An unmagnetised magnetic material can be magnetised by placing it in a magnetic field.
What force of attraction does induced magnetism cause?
Will cause a force of attraction between any unmagnetised magnetic material placed near one end of a bar magnet. The force is always attractive force whichever end of the bar magnet is nearest to the material.
What happens to the magnetic field lines when you reverse the current?
The magnetic field lines reverse direction when the direction of the current is reversed.
What happens to the magnetic field when you increase the current?
Becomes stronger everywhere.
The plotting compass turns more and more away from North as the current becomes stronger. This is because the field has a bigger effect on the plotting compass than the Earth’s magnetic field does.
What is a solenoid?
A solenoid is a long coil of insulated wire. The magnetic field is produced in and around the solenoid when a current is passed through the wire.
Explain the inside of the solenoid.
The magnetic field is much stronger than if the wire was straight. The field lines are parallel to the axis of the solenoid, and they are all in the same direction. The magnetic field inside the solenoid is strong and uniform.
Explain the outside of the solenoid.
The magnetic field lines bend around from one end of the solenoid to the other end of the solenoid. Each field lines is a complete loop because it passes through the inside of the solenoid.
Why are the magnetic field lines in a complete loop on a solenoid?
Because it passes through the inside of the solenoid.
What is an electromagnet?
An electromagnet is a solenoid in which the insulated wire is wrapped around an iron bar (the core). When a current is passed along a wire, a magnetic field is created around the wire. Because of this, the magnetic field of the wire magnetises the iron bar. When the current is switched off, the iron bar loses most of its magnetism.
What are four uses of an electromagnet?
The scrapyard crane
The circuit breaker
The electric bell
The relay
What is the scrapyard crane?
A use of electromagnets:
Scrap vehicles are lifted in scrap yards using powerful electromagnets attached to cranes. The steel frame of a vehicle sticks to the electromagnet when current passes through the coil of the electromagnet. When the current is switched off, the vehicle frame falls of the electromagnet.
