Magnetism Flashcards
What is magnetism?
The ability of magnets to attract and repel other magnets without physical contact
What do magnets produce?
Magnetic field
What does a magnetic field make other magnets or magnetic materials experience?
A force
Why do opposite poles attract when 2 magnets are close?
Magnetic fields overlap
What is created when opposite poles are placed near each other?
A uniform field
What is a uniform field?
A magnetic field that is the same everywhere between the poles
How do you tell if an object is a magnet?
It will attract magnetic materials and repel one pole of another magnet
What causes there to be magnetic forces?
Magnets producing magnetic field
What are magnetic forces?
Forces between magnets
Where is the magnetic field strongest?
Poles
Where are the magnetic forces strongest?
Poles
What do permanent magnets always produce?
A magnetic field
When a magnetic material is in a magnetic field, what does it become?
Induced magnet
What do permanent magnets create in magnetic materials?
Temporary poles which align so the magnetic material is attracted to the permanent magnet
Why is the force between a magnet and magnetic material always attractive?
Magnetic induction- the South Pole induces a North Pole in the magnetic material and vice versa
What are induced magnets?
Magnetic materials that produce a magnetic field in a magnetic field
What happens to an induced magnet when a permanent magnet is taken away?
They return to normal and don’t produce a magnetic field
What materials quickly use magnetism?
Magnetically soft materials eg iron, nickel and iron alloys
What materials slowly use magnetism?
Magnetically hard materials like steel
3 main magnetic elements
Iron, nickel, cobalt
What are magnetic materials always attracted to if they are within the magnetic field?
A magnetic
Are magnetic materials repelled?
No
What is inside a plotting compass?
A tiny bar magnet called a needle that lines up with the magnetic field it’s in
Why will the needle of a compass point in the direction of the North Pole when not near a magnet?
The earth’s core is magnetic so it generates its own magnetic field
What does an electric current produce?
A magnetic field
What will a wire have created around it when a current flows through it?
A magnetic field
What will the magnetic field lines created in a wire with a current look like?
Concentric circles perpendicular to the wire in the centre
What increases the strength of the field in a wire with a current flowing through it?
Larger current and closer to the wire
What does changing the direction of the current change?
The direction of the magnetic field
To find the direction of the current what rule is used?
Right hand thumb rule
What is a solenoid?
A loop of wire coiled into a cylindrical shape that carries an electric current
What increases the strength of the magnetic field in a solenoid?
More loops
Where is the magnetic field weak in a solenoid?
Outside the solenoid apart from at the ends
Where is the magnetic field strong in a solenoid?
Inside
What increases magnetic field strength in a solenoid?
Increasing current, putting an iron block in the centre of the coil
Why does an iron core increase magnetic field strength in a solenoid?
Becomes an induced magnet when current flows
What decreases magnetic field strength of a solenoid?
Increased distance from the solenoid
The invention of what has increased the use of magnetic materials?
Electromagnets
What is an electromagnet?
A type of magnet in which the magnetic field is produced by an electric current so can be turned on and off
3 objects that use electromagnets
Fridge doors, maglev trains, MRI machines
What is the motor effect?
When a current-carrying conductor is put between the poles of 2 magnets so the magnetic fields interact and the magnet and conductor experience a force
What causes the motor effect?
The magnetic field created by a current interacting with a magnetic field
To experience the motor effect what angle must the wire be at to feel the full force?
90 degrees to the magnetic field
If the wire runs parallel to the magnetic field, what force will it feel?
None
What does the direction of the force on the wire depend on?
The direction of the magnetic field and direction of current flow
What rule determines the direction of force of the motor effect?
Fleming’s left hand rule
What is Fleming’s left hand rule?
First finger= magnetic field
Second finger = current
Thumb = force (direction conductor would move)
What does the size of the force on a conductor in a magnetic field depend on?
Magnetic flux density, current size and length of conductor
What is the magnetic flux density?
Strength of magnetic field
What is the force on the wire directly proportional to?
The magnetic flux density, the current and the length
When the current is at 90 degrees to the magnetic field, what equation can be used to find the force acting on it?
Force = magnetic flux density x current x length
Why does a solenoid rotate on its axis?
Its experiences a force
How can the size of the turning force on the solenoid be increased?
Increasing current
Increasing magnetic flux density
Increasing number of coils
What is electromagnetic induction?
The creation of a potential difference and current in a wire experimenting a charge in a magnetic field
How can a potential difference be induced?
Moving a conductor
Rotating a magnet in a coil of wire
Changing magnetic field through an electrical conductor
How is a pd induced in transformers?
The magnetic field strength is increased or the charge speed is increased or more turns in a coil of wire
What does the induced pd create?
A force which acts in the opposite direction to the action that induced it
Why does the induced pd create a force which acts in the opposite direction to the action of that induced it?
Motor effect
What direction does the force induced by the motor effect run?
Opposite to the inductive force’s direction
What do transformers change?
The potential difference in wires carrying alternating currents
How do transformers change pd?
Induction
What are transformers made up of?
2 coils- primary and secondary- was hat are joined by an iron core
Describe the transformer process
Alternating pd/ current applied to primary coil
Alternating current flows through primary coil creating an alternating magnetic field
Alternating magnetic field in iron core due to alternating current
Alternating magnetic field passes through secondary coil due to alternating current
Alternating pd and magnetic field induced in secondary coil
How efficient are transformers?
100%
Why are transformers 100% efficient?
All energy transferred to the transformer by the primary coil will be transferred to any component connected to the secondary coil
What is equal in each coil?
Power
Equation for voltage and number of coils in transformers
Voltage primary / voltage secondary
=
Number primary coils / number secondary coils
