Physics Magnetism March 2019 Flashcards
What materials are magnetic?
Iron, steel, cobalt and nickel.
What are the basic facts about magnets?
- They have two poles: North and South.
- Opposite poles attract, similar poles repel.
- Magnetism is an non-contact force.
- Magnetic materials are attracted to both ends.
How do you plot magnetic field patterns?
- Get a plotting compass.
- Place the compass at the north or south pole.
- Put a dot where the arrow points on the compass then move the compass to that position and repeat.
- Join the dots and draw an arrow from north to south.
`What is a magnetic field pattern?
Lines that show the force around the magnet. The closer the lines the stronger the magnetic field. The lines always point from north to south.
What are the different types of magnets?
Permanent magnets = Never lose magnetism, have their own magnetic field and have a north and south poles.
Induced magnets = Material made into a magnet by being placed in a magnetic field, lose magnetism after a while and always attract permanent magnets.
Why is there a magnetic field around a current carrying wire?
Electric current flowing through a wire induces a magnetic field around it. The current always flows from + to -. The pattern is circular. The field is weaker further away from the wire. The direction of the field depends on the direction of the current.
What is the right hand rule?
Used to find the direction of a magnetic field around a current carrying wire.
- Point thumb in the direction of the current (+ to -).
- Curl other fingers around wire. The direction of the curl shows the direction of the field.
What is a solenoid?
A long coil of wire that creates a magnetic field when current flows through it. It has a similar pattern to a bar magnet and is a simple electromagnet.
How are electromagnets made? What are their advantages and uses?
Made by - Taking an iron core and wrapping it in coils connect to a power supply. Turn on the power and the iron core is magnetised.
Advantages - Can turn magnetic field on/off and can vary magnetic field strength (Add more coils/put coils closer together/use a softer iron core).
Uses - Relays (car starter motors), scrapyard for carrying and lifting, doorbell and loudspeaker.
What is magnetic flux density?
The lines on a magnetic field are called magnetic flux. The strength of the magnetic force is called the flux density ß (based on how close the lines are).
What is magnetic flux density measure in?
Teslas or T. A bar magnet has a flux density of 0.1 T.
What is Fleming’s left hand rule?
A rule to remember which way the force acts in the motor effect:
Thumb = Motion.
First finger = Direction of magnetic field (N to S).
Second finger = Direction of current (+ to -).
What is the motor effect?
When current flows through a wire which is between a magnet, a magnetic field is created which interacts with the magnetic field of the magnet so the wire experiences a force. This is called the motor effect.
The force will act in the opposite direction if the current or magnetic field is reversed.
What is the formula for the motor effect?
F = BIL
Force = magnetic flux density x current x length of wire in field.
What is electromagnetic induction?
Electromagnetic induction is how potential difference is made across a wire. It can be made by moving the wire across a magnetic field or changing the magnetic field around the wire. This allows current to flow through the wire.
