Magnetism Flashcards
(22 cards)
Describe 2 ways you can find the shape of a magnetic field
Iron filings
Plotting compasses
Name 2 electrical devices that use magnets
Motors
Loudspeakers
Magnetic field lines point from ——— to ———- ?
North to south
Where is the field strongest
Where the lines are closest together
Name 3 magnetic elements
Iron cobalt nickel
What is an induced magnet
A magnet which is only a magnet because it is in the field of another magnet
What is a solenoid
A coil with a current flowing through it
Name the 3 things that affect the strength of an electromagnet
Number of turns on coil
Size of electric current through coil
Material of core
What shape is a magnetic field around a wire with a current flowing through it
Circular
Where is the field strongest on an electromagnet
Down the middle
(It is also uniform down the middle)
What rule gives the direction of the magnetic field around the wire
The right hand thumb rule
(Thumb being direction of current)
What rule gives the direction of force felt
Flemings left hand rule
(Third finger is current and thumb is force)
What are the 3 elements other than the magnet needed for an electric motor
Dc supply
Commutator
Brushes
How does an electric motor change the polarity of the electromagnet
When the brushes pass from one plate on the commutator to the other (gaps) this causes a polarity switch
Describe method using plotting compass to find the magnetic field of a magnet
- Place plotting compasses near the magnet on a piece of paper
- Mark the direction the compass needle points
- Move the plotting compass to many different positions in the magnetic field, marking the direction of the needle each time
- Join the points to show field lines
Describe the motor effect
A wire carrying a current creates a magnetic field.
This can interact with another magnetic field, causing a force that pushes the wire at right angles.
This is called the motor effect
When does the force on a given length of wire increase when in a magnetic field
Current in the wire increases
Strength of the magnetic field increases
What is a permanent magnet
Poles which are north and south all the time
How does a microphone depend on sound and electrical energy
A microphone transfers sound waves into an electrical signal
How does a loudspeaker depend on sound and electrical energy
A loudspeaker converts an electrical signal into sound waves
How does a microphone work
As the diaphragm moves in and out a varying pd is induced across the ends of the wire, producing a varying electric current
The varying electrical current then travels through the wires until it reaches the loudspeaker
How does the diaphragm move in and out in a microphone
The sound wave is made up of areas of high and low pressure
The high pressure areas push the diaphragm in and the low pressure areas cause it to move outwards
