Section 6 - Magnetism and Electromagnetism P1 Flashcards
What two poles do all magnets have?
A north and south
Define magnetic field:
It’s a region where magnetic materials experience a force
What are the metals that are magnetic materials?
- iron
- steel
- nickel
- cobalt
What are magnetic field lines used to show?
Show the size and direction of magnetic fields
-ALWAYS POINT FROM NORTH TO SOUTH
What does placing the north and south poles of two bar magnets near each other create?
-creates a uniform field between the two magnets
Describe a practical for how magnetic field lines can be seen using compasses:
- compasses and iron fillings align themselves with magnetic fields
- can use multiple compasses to see the field lines coming out of two bar magnets
- could use iron fillings on a piece of paper with a magnet below and you can see the field lines
What do magnets affect?
Magnetic materials and other magnets
What do like poles do, and what do opposite poles do?
Like poles - repel
Opposite poles - attract
What are magnetic materials attracted to?
Both poles attract magnetic materials
- the material acts like a magnet when it is brought near to a magnet
- the magnetism has been induced by the original magnet
What affects induced magnetism?
distance
-the closer the magnet and magnetic material get the stronger the induced magnetism will be
What does an electric current in a conductor produce?
A magnetic field around it
What affects a magnetic field around an electric current flowing through a wire?
- larger current, stronger magnetic field
- direction of current, determines direction of magnetic field
What are the two ways magnetic materials can be described?
soft - if it looses its magnetism quickly
hard - if it keeps its magnetism permanently
What is an example of a soft magnetic material?
iron
What is an example of a hard magnetic material?
steel
What material is used in transformers?
iron - because for mains electricity it needs to be magnetised and demagnetised 50 times er second
How can you increase the strength of a magnetic field around a solenoid?
By adding a soft iron core
When a current-carrying wire is put between magnetic poles, what happens?
-the two magnetic fields affect one another
-the result is a force on the wire
-this causes the wire to move
THIS CALLED THE MOTOR EFFECT
What angle does a wire have to be at within two magnetic poles to experience the full force?
90° to the magnetic field will experience full force
- parallel won’t experience any force
- angles in between will feel some force
What factors determine the way that the force will affect the wire between two poles?
- the magnetic field of the magnets
- the direction of current in the wire
What factors increase the magnitude of the force that the wire will get when a current is flowing through it when it’s between two poles?
- increasing the strength of the magnetic field
- increasing the amount of current flowing through the conductor
What can you do to determine the direction at which the force acts from the motor effect?
Fleming’s left hand rule
- use your left hand
- point your first finger in the direction of the field
- point your second field in the direction of the current
- point your thumb in the direction of the force (motion)
What direction does a magnetic field go?
From north to south
What direction does current go?
From positive to negative
What factors speed up a DC electric motor?
- more current
- more turns of the coil
- stronger magnetic field
- a soft iron core in the centre
How does a DC electric motor work?
- a coil of wire is placed between a north and south pole
- the forces act one up and the other down, it rotates
- the split-ring commutator keeps the motor rotating in the same direction
What does a split-ring commutator do?
It swaps the contacts every half turn to keep the motor rotating in the same direction
How can the direction of a DC motor be changed?
- swapping the polarity of the DC supply
- swapping the magnetic poles over
How do loudspeakers work?
AC electric signals from an amplifier are fed to a coil of wire in the speaker, which is wrapped around the base of a cone
- the coil is surrounded by a permanent magnet
- this causes the coil to move back and forth
- the movements cause the cone to vibrate which creates sound
Define electromagnetic induction:
The creation of a voltage (and maybe a current) in a wire which is experiencing a change in magnetic field.
What is the dynamo effect?
Using electromagnetic induction to generate electricity using energy from kinetic energy stores is called the dynamo effect. (in a power station, this energy is provided by the turbine)
What two situations do you get electromagnetic induction?
- when an electrical conductor moves through a magnetic field
- when the magnetic field goes through an electrical conductor changes
How can you test the dynamo effect?
You can test the dynamo effect by connecting an ammeter to a conductor and moving the conductor through a magnetic field (or a magnet through the conductor)
-the ammeter will show the magnitude and direction of the induced current
How can you get a bigger voltage from the dynamo effect?
increasing. ..
- the strength of the magnet
- the number of turns of the coil
- the speed of the movement
How do AC generators work?
- generators rotate a coil in a magnetic field
- as the coil spins, a current is induced by the coil, this current changes direction every half turn
- AC generators have slip rings and brushed so the contacts don’t change every turn
- this results in the production of AC voltage
What type of electricity do power stations generate?
AC because they use AC generators
-they just get the energy needed to turn the coil or magnetic field in different ways
