Flashcards in Magnetism And Electromagnetism Deck (30)
What is a magnetic field?
-region where magnets and magnetic materials experience a force (non contact)
What poles do magnets have?
-North and South
How could you show a magnetic field?
-place a bar magnet under a piece of paper
-shake iron fillings onto top of paper
-will see the force lines of the magnet and where the strongest magnetic field is
-strongest magnetic field is at the poles of the magnet (lines are closer together)
What happens when a North magnet is placed near a South magnet?
-exert a force on each other (attractive or repulsive)
-two unlike poles will attract each other strongly
-two like poles will repel each other
What is the magnetic North Pole on a compass?
The geographic South Pole (opposites)
What does a current carrying conductor have?
-circular magnetic field around it
-direction of field depends on direction or current
-if current coming towards you, the circular field is anti clockwise
Where is the magnetic field in a coiled wire (solenoid)?
-goes through centre of coil
-if magnetic field in a clockwise direction, the magnetic field direction through coil is away from you
What is the right hand thumb rule?
using right hand, point thumb in direction of current and curl your fingers. The direction of fingers is the direction of the field
What is a permanent magnet?
-They are magnetic all the time
-used as fridge magnets to hold things
-produce their own magnetic field
What is an electromagnet?
-a magnet where the electrical current can be switched on and off (isn't permanent)
-used in scrapyards when metal is being dropped
How do you make an electromagnet?
-wrap wire around an iron nail into a coil (solenoid) and connect it to a power supply
-the current allows the nail to become magnetic when power supply is switched on
-produced a magnetic field in iron core
How can you increase the strength of an electromagnet?
-increasing the number of coils it has (the closer the field lines, the stronger the field)
-increasing the current
-place a block of iron in the centre of the coil and iron core becomes an induced magnet when the current is flowing
What happens in the circuit of an electric bell?
-electromagnet attracts arm of the striker towards the bell
-as striker moves towards bell, circuit contact is broken and striker springs back
-contact is remade and striker is attracted again and hits the bell and breaks circuit again
What is an induced magnet?
Magnetic materials that turn into a magnet when they're put into a magnetic field
What happens when you take away the magnetic field?
Induced magnet quickly loses most or all of their magnetism (eg in scrap yards)
How is an electromagnet used in a relay switch?
-used to enable a circuit with small current (eg light sensor) to switch on a circuit with a larger current (eg street lamp)
-when small circuit is switched on, activated electromagnet which pulls contacts of switch in the large circuit together (switching it on)
What material is needed to create an electromagnet?
-easily magnetised and demagnetised
-soft iron is the best as it doesn't have many impurities
-steel not as good as it retains some magnetism when current is turned off
What does the direction of magnetic field depend on?
The direction of the current
How could you investigate the magnetic field between four bar magnets?
-put magnets on a piece of paper and place many compasses in different places between magnets to show magnetic field at those points
-compass needles will line up with magnetic field lines
What is the motor effect?
When a current carrying wire is put between magnetic poles, the magnetic field around the pole interacts with the magnetic field it has been placed in
-this causes magnet and the conductor to exert a force on each other
-motor effect can cause wire to move
What is Flemming’s left hand rule?
Using left hand, point first finger in direction of field
Point second finger in direction of current
Your thumb will then point in direction of the force (motion)
How do you find the size of a force acting on a conductor in a magnetic field?
Force =magnetic flux density (Tesla) X current X length
What is the generator effect?
The induction of a potential difference (and current if there’s a complete circuit) in a wire which is experiencing a change in magnetic field
What is a generator?
Rotated a coil in a magnetic field or a magnet in a coil
What is a dynamo?
They have a slip ring commutator instead of slip rings which swaps connection every half turn to keep current flowing in same direction
What does a transformer do?
Uses the generator effect to change size of a pd. They will only work with alternating current
What do transformers always have?
Two coils of wire, the primary and secondary, joined with an iron core
What is the transformer equation?
Input pD/output pD = no of turns in primary coil / no of turns in secondary coil
What does a step up transformer do?
Step the pd up. Have more turns on secondary coil then primary coil