Topic 11 - Magnets Flashcards
Magnet?
can exert a force on another nearby magnet.
Magnets have two poles:
north and south
The rules of magnetism (2)
like poles (N–N or S–S) repel
unlike poles (N–S or S–N) attract
What type of forces are magnetic forces?
Magnetic forces are non-contact forces - this means that magnets affect each other without touching.
If a magnet is cut in half what happens?
S-N and S-N
NOT
S and N
What is a permanent magnet?
is often made from a magnetic material such as iron. A permanent magnet always causes a force on other magnets or magnetic materials.
Example of permanent magnet?
Bar magnets and horseshoe magnets
Key features of permanent magnet?
it produces its own magnetic field
the magnetic field cannot be turned on and off – it is there all the time
Testing for magnetism?
Putting a magnetic near see if it repels or attracts
Magnetic field?
is the region around a magnet where a force acts on another magnet or on a magnetic material.
Temporary magnet?
a material that can only be temporarily magnetized, and loses its magnetism when the magnetic field is removed
Detecting magnetic fields (4)
- Place the plotting compass near the magnet on a piece of paper.
- Mark the direction the compass needle points.
- Move the plotting compass to many different positions in the magnetic field, marking the needle direction each time.
- Join the points to show the field lines.
The diagram shows these key features of a magnetic field (4)
- the magnetic field lines never cross each other
- the closer the lines, the stronger the magnetic field
- the lines have arrowheads to show the direction of the force exerted on a magnetic north pole
- the arrowheads point from the north pole of the magnet to its south pole
The fleming left hand rule?
middle finger = current
thumb = force
index finger = magnetic field
How does a DC motor work?
take electrical power through direct current, and convert this energy into mechanical rotation.
Explain The magnetic field around a current-carrying wire?
This magnetic field can deflect the needle of a magnetic compass. The strength of the magnetic field is greater closer to the wire, and increases if the current increases.
When a magnet moves through a conduction coil: (4)
- Bulb lights up
- Current starts flowing in circuit
- Voltage is induced in the circuit
(same thing happens if the coil moves instead of magnet)
Magnetic field changing due to…
- When the magnet field changes due to a magnet or conductor moving, a voltage is induced in the circuit
Movement (2)
- Voltage or current is induced in the coil only when there is relative motion
- No motion = no induced voltage or current
Direction
- When the direction of motion is reversed the voltage induced turns to the oppiste sign (+ or -)
Direction of the induced voltage of current depends on: (2)
- Orientation of the poles
- Direction of motion
Factors on which size of induced voltage depends: (5)
- Speed of movement
- Strength of magnetic field
- Number of turns in a coil
- Area of coil
(ALL THESE FACTORS INCREASE THE VOLTAGE INDUCED)
Explain how the AC generator works? (4)
- A coil rotates inside a magnetic field (created by two magnets).
- The coil cuts through magnetic field lines, which induces a voltage in the coil (Faraday’s Law).
- The current changes direction every half turn because the sides of the coil move in opposite directions relative to the magnetic field.
- A pair of slip rings ensures the current flows smoothly as the coil rotates, producing alternating current (AC)
How can the induced current produced in an AC generator be increased? (4)
- Increasing the speed of rotation
- Using a stronger magnet
- Increasing the number of turns in the coil
- Using a coil with a larger area
Type of current in an AC vs DC?
AC = Produces alternating current (AC), which changes direction.
DC = Produces direct current (DC), which flows in one direction.
Current flow in an AC vs DC?
AC = The current direction keeps changing as the coil rotates.
DC = The commutator flips the connection every half turn, making the current always flow in the same direction.
Connections in an AC vs DC?
AC = Uses slip rings (two separate metal rings) to keep the circuit connected smoothly.
DC = Uses a split-ring commutator (a ring cut in half) to reverse the connection and keep the current flowing in one direction.
6 parts of an AC generator?
- Coil (Armature)
- Magnet (Field Magnet)
- Slip Rings
- Carbon Brushes
- Turbine
Coil function?
Rotates inside the magnetic field and cuts the magnetic field lines, generating electricity.
Magnet function?
Provides the magnetic field needed for induction. It can be a permanent magnet or an electromagnet.
Slip rings function?
Connected to the ends of the coil and allow the coil to rotate freely while maintaining electrical contact.
Carbon brushes function?
Press against the slip rings and transfer the generated AC current to an external circuit.
Turbine function?
Rotates the coil, usually powered by a mechanical source like wind, water, or steam.
