P2: Magnetism & Electromagnetism Flashcards
The microphone is used to convert the pressure variations in sound waves into variations in ______
Current.
What material is used in the core of a transformer?
Iron, because it is easily magnetised
Why do we use iron as the core in a transformer?
Because it is easily magnetised.
What is a solenoid?
A long insulated coil of wire.
List some of the magnetic metals.
Iron, cobalt, nickel.
What is induced magnetism?
When an object becomes magnetic when it is placed in a magnetic field.
How is induced magnetism lost?
When the magnet moves out of the magnetic field.
Where is the magnetic force of a magnet at its strongest?
Near its poles.
What is the direction of magnetic field lines?
North to South
What type of force is magnetism?
Non-contact.
How can you show that an object is a permanent magnet?
By checking if it repels another magnet.
What equipment do you need to draw out magnetic field lines?
A bar magnet, a plotting compass, paper and a pencil.
The closer the field lines, the __ the magnetic field.
Stronger.
What is Fleming’s left hand rule?
-Thumb shows direction of Force
-First finger shows direction of Magnetic Field
-Second finger shows direction of Electrical Current
What strengthens the magnetic field of a wire?
-Increasing current of the wire.
What is an electromagnet?
A solenoid with an iron core.
What is the motor effect?
Where a force is exerted on a current-carrying wire due to the presence of a magnetic field.
What increases induced potential difference in a generator?
-Increasing the speed of movement
-Increasing the magnetic field strength
-Increasing the number of turns on the coil.
What is a transformer?
A device that can change the potential difference or voltage of an alternating current.
The higher the current in a cable, the greater the what?
The greater the energy transferred to the surroundings by heating.
How does the National Grid reduce energy transfers to the environment?
Uses transformers to increase the voltage and lower the current when travelling through transmission cables.
How does a transformer work? (8 steps)
An alternating current flows in the primary coil.
This creates a magnetic field that is changing in strength and direction.
This field interacts with the secondary coil.
The secondary coil experiences a change in magnetic field.
The coil “cuts” through magnetic field lines.
This induces a potential difference.
If there is a complete circuit, a current is also induced.
If there are more turns on the secondary coil than the primary, the voltage is “stepped up”.
Explain how a microphone works. (6 steps)
Sound waves vibrate the diaphragm.
The diaphragm moves the coil.
The coil experiences a change in magnetic field.
The coil “cuts” through magnetic field lines.
This induces a potential difference.
If there is a complete circuit, a current is also induced.
Explain how a generator works. (5 steps)
A coil is moved in a magnetic field.
The coil experiences a change in magnetic field.
The coil “cuts” through magnetic field lines.
This induces a potential difference.
If there is a complete circuit, then a current is also induced.
Explain how a speaker works. (6 steps)
A current passes through the coil.
This current creates a magnetic field.
This magnetic field interacts with the magnetic field formed by the permanent magnet.
This causes a force on the coil.
The current is alternating and changes direction, which changes the direction of the magnetic field and therefore the force.
The changing force vibrates the cone, which causes air particles to vibrate and creates sound.
Explain how a motor works. (6 steps)
A current passes through the coil.
This current creates a magnetic field.
This magnetic field interacts with the magnetic field formed by the permanent magnet.
This causes a force on the coil.
The force causes the coil to rotate.
The split ring commutator reverses the current every half turn to keep the coil spinning in the same direction.
