Paper 1 - Magnetism and Electromagnetism Flashcards
Describe how to use 2 permanent magnets to produce a uniform field line
- Position magnets parallel to each other on a sheet of paper
- Evenly and slowly sprinkle iron filings over the magnets
- Tap the surface of the paper to reveal the magnetic field lines
What is the relationship between permanent and temporary magnets?
They always attract
Describe the properties of magnetically soft substances
- Temporary magnets
- Only have a magnetic field line temporarily
- Need another magnetic field to become magnetic
Describe the properties of magnetically hard substances
- Permanent magnets
- Always produce their own magnetic field
What do unlike poles do?
Attract
What do like poles do?
Repel
What is the relationship between charge, current and time?
Q = It
Give some disadvantges of underground electrical energy transmission
- Hard to set up
- Expensive to set up
- Hard to access
How does current create sound waves in a loudspeaker?
- As the current passes through the coil, it generates a magnetic field
- The magnetic field from t he coil now interacts with the magnetic field from the permanent magnet
- These magnetic fields attract and repeal each other 50 times per second because a.c. is @ 50Hz
- This produces a resultant force on the cone
- This causes the cone to move in and our
Give some disadvantages of overhead energy transmission
- Cannot be insulated
- Can be damaged by weather
- Visual pollution
Give some advantages of underground electrical energy transmission
- Can be insulated
- Cannot be damaged by weather
- More reliable
When is a voltage induced in a coil or conductor?
- When the voltage moves through a magnetic field
or - When a magnetic field changes through the voltage
Give some advantages of overhead electrical energy transmission
- Easy to set up
- Cheap to set up
- Easy to access
- Minimal habitat disturbance
What is a magnetic field line?
The region around a magnet where a force acts on another magnet or on a magnetic material
What factors affect the size of the induced voltage?
- Strength of the magnet
- Speed at which magnetic field lines are cut
- Number of turns in the coil
Describe the generation of electricity by the rotation of a magnet within a coil of wire
- Magnetic moves through a coil
- Magnetic field lines are cut by the coil
- Charged particles in the wire experience a force
- Which induced a voltage
- Whch generated electricity
What happens when there is an electric current in a conductor?
A magnetic field is produced around it
Describe how the force on a current-carrying conductor in a magnetic field changes with the magnitude and direction of the field and current
- If you increase the magnitude of the current through a wire or the size of the magnet being used, you increase the force on the wire.
- If you change the direction of the current or reverse the poles of the magnet, you change the direction of the force on the wire
What is the purpose of the brushes in a d.c. motor?
The brushes provide a connection to the rotating commutator / coil
What is the purpose of the commutator in a d.c. motor?
The commutator reverses the direction of the current once every half-turn
What are some advantages of a thick wire?
- It reduces resistance
- A thin wire may melt
- A thin wire may bend
What happens to the value for induced current when the polarity of the magnets is reversed?
- Becomes negative
- E.g. 2 mA becomes - 2 mA
