Magnetism and Electromagnetism Flashcards
(27 cards)
The strongest parts of metals are its ________
Poles
Permanent magnets are made up of ___________. Example:
Magnetically hard material eg. steel
Iron is a magnetically __________ and can therefore be only used as a ______________
soft material
temporary magnet
What is a magnetic field?
A volume of space around a magnet where magnetism can be detected
Two ways to show the patterns of the magnetic field around a magnet:
Iron filings
Small compasses
Main features of the magnetic field lines:
- Show the shape of the magnetic field
- Show the direction of the magnetic force
- Show the strength of the magnetic field
What is the neutral point in a magnetic field?
It is the point where forces of both magnets cancel out and so there is no resultant magnetic field/force there
How can we make a uniform magnetic field?
By taking the opposite poles of two magnets and holding them close together
What are the features of a uniform magnetic field?
- Its strength and direction are the same at all points
What is induced magnetism?
Induced magnetism is when a permanent magnet is brought near to a magnetic material that becomes temporarily magnetized
What is electromagnetism?
Electromagnetism is a phenomenon that occurs when a magnetic field is created around a wire that has a current flowing through it
The features of a magnetic field created around a current-carrying wire:
- Has a definite direction from N to S
- Quite weak
- Circular in shape
- Can change directions if the direction of the current flowing through it changes
The strength of a magnetic field around a current-carrying conductor can be increased by:
- Increasing the current in the wire
- Wrapping the wire into a coil or a solenoid
The strength of a magnetic field around a solenoid can be increased by:
- Increasing the current in the solenoid
- Increasing the no. of turns on a solenoid
- Wrapping the solenoid around a magnetically soft core such as an iron
Advantages of an electromagnet over ordinary magnets:
- It can be turned on and off
- Its magnetic field can be changed
Uses of electromagnets:
Electric bell
Circuit breaker
How is movement generated from electricity?
When a charged particle passes through a magnetic field, it experiences a force as long as its motion is not parallel to the field
Explain the motor effect
When the two magnetic fields overlap, in some places where the direction of the magnetic field is the same, they reinforce each other, and where the magnetic fields are in opposite directions, a weaker force is produced. Due to the different strengths of the magnetic field, the wire feels a force acting on it from the stronger part to the weaker one
Explain the functioning of a moving coil loudspeaker
- Electric currents from a source are supplied to the speaker’s coil
- These currents are always changing in direction and strength
- The overlapping magnetic field are also always changing direction and strength
- These fields, in turn, apply rapidly changing forces to the wires of the coil which cause the cone to vibrate
- These vibrations create the sound waves we hear
The function of a split-ring commutator:
It connects the loop of wire to the electrical supply. The gap in the split-ring commutator changes the connections, the direction of the current flowing in the loop reverses which then reverses the direction of force acting on each side of the loop. The loop rotates continuously
How can the size of induced voltage be increased?
- Move the wire more quickly
- Use a stronger magnet so more field lines are cut
- Wrapping the wire into a coil so that more pieces of wire cut through the magnetic field lines
How does a dynamo work in bicycles?
The motion of the wheel causes a rotating magnet to turn. As it turns, so does the magnetic field. It cuts through the coil and induces a current in it that can then be used to light up the bicycle lights
How do transformers work?
The alternating current in the primary coil creates a growing and collapsing field around the primary coil which cuts through the secondary coil. This induces an alternating output voltage in the secondary coil
What is the function of transformers?
Transformers change the size of the alternating voltage by using different no. of turns in the primary and secondary coils
