Topic 7- Magnetism and Electromagnetism

Created by

Khloe

Cards (41)

What direction does the magnetic field flow in?
North into South
What is a permanent magnet?
A magnet that can produce its own magnetic field.
What is an induced magnet?
A material that becomes magnetized when placed in a magnetic field.
What is the right-hand thumb rule?
-point thumb in the direction of the current and curl fingers
-the direction the fingers curl in is the direction of the magnetic field
What is a solenoid?
A coil of wire that produces a magnetic field when an electric current passes through it.
How do you increase the strength of a solenoid?
Increase the number of turns on the coil, increase the current, add a metal core
What can the metal core be made out of in a solenoid?
Iron, nickel, cobalt
What does each finger represent on Flemming's left hand rule?
Thumb: Direction of force experienced by the wire Index finger: Direction of magnetic field Middle finger: Direction of current
What is the motor effect?
The effect that causes a wire carrying a current to move when placed in a magnetic field.
What is the magnetic flux density?
The magnetic flux density is the amount of magnetic field passing through a given area- shows the strength
What is the current?
Flow of electric charge.
What is the equation for the force experienced by a wire in a magnetic field?
F= BIL
force= magnetic flux density * current * length
What are some uses for electromagnets?
Electric motors, separating metals, speakers, and magnetic locks.
What is a transducer?
A device that converts one form of energy into another.
What do loudspeakers and microphones use to convert variations in current to sound waves?
The motor effect.
How does a loudspeaker work?
uses the motor effect
-AC current in wire
-changes polarity of magnetic field around wire
-interacts with magnetic field of the magnet
-causes movement and vibrations in the cone, creating sound waves
How does a microphone work?
-persons voice causes the membrane to vibrate
-causes wire to move in the magnetic field
-induces potential difference in wire, creating an AC current
-sound waves are converted into electrical signals
What is the generator effect?
Where moving a wire in a magnetic field induces potential difference
What is a generator?
A device that converts kinetic energy into electrical energy.
What do compasses show? 
The directions of magnetic fields
What does a moving charge create? 
A magnetic field
What is an electromagnet? 
A magnet powered by electricity.
What are electromagnets used for? 
-used in cranes to attract and pick up things made from magnetic materials (in scrap yards)
-used within other circuits to act as switches
What is the generator effect? 
The induction of a potential difference in a wire which is moving relative to a magnetic field, or is experiencing a change in a magnetic field
How do you create the generator effect? 
By moving a magnet in a coil of wire or moving a wire in a magnetic field
What happens when you flip a magnet in a magnetic field?
The poles will switch, which in turn reverses the direction of the potential difference or current
What does an induced current always do?
Opposes the charge that caused it
How do you change the size of an induced potential difference? 
-increase the speed of movement
-increase the strength of magnetic field
What do alternators do? 
Rotate a coil in a magnetic field to produce an alternating potential difference
What do dynamos do?
Generate electricity- a direct current produced using split-ring commutator
How do alternators work? 
-construction is like a motor
-as the coil or magnet spins, a current is induced in the coil
-current changes direction every half-turn
-have slip rings and brushes so the contacts don't swap every half turn
What do oscilloscopes show? 
Show how potential difference generated in a coil changes over time
What is the shape of an alternating current on an oscilloscope graph?
Goes up and down across the horizontal axis
What is the shape of a direct current on an oscilloscope graph? 
Goes up and down but always stays above the graph (as it's always positive)
How do microphones generate current from sound waves? 
-sound waves hit flexible diaphragm that is attached to a coil of wire, wrapped around a magnet
-causes coil of wire to move in the magnetic field which generates a current
-the movement of the coil depends on the properties of the sound wave (louder sound moves diaphragm further)
-microphones can convert the pressure variations of a sound wave into variations in current in an electric circuit
What do transformers do?
Change the size of potential difference of an alternating current
What coils of wire do transformers have? 
Primary and secondary coils, joined with an iron core
What do step-up transformers do? 
Increase the potential difference- more turns of wire on the secondary coil
What do step-down transformers do? 
Decrease the potential difference- more turns of wire on the primary coil
What is the efficiency of a transformer?
Almost 100% efficient