Magnetism and Electromagnetism Flashcards
State the SI units for the following Current Voltage Power Amps Volts Watts
I V P A V W
What do magnets do?
Repel and attract other magnetic substances
Opposite poles attract and poles that are alike repel
What substances can be magnetised
Nickel
Iron
Cobalt
and their alloys e.g. Steel
What do you call…
A magnet that can be temporarily magnetised
A magnet that can be permanently magnetised
Magnetically Soft
Magnetically Hard
What to magnetic field lines show
The direction of a magnetic field (from north to south)
The spacing between adjacent field lines indicate the strength of the magnetic field
Describe an experiment to investigate the magnetic field pattern around a bar magnet using iron filings
- Place a bar magnet under a piece of waxy paper
- Lightly sprinkle iron filings onto the waxy paper
- Then gently heat the waxy paper over a Bunsen burner -until the iron filings are set into the paper
- This will show you the field line but not the direction
How can we produce a uniform magnetic field pattern?
Using two permanent magnets (2 wide and close opposite poles (field lines go from north to south)
What does an electric current in a wire produce?
It produces a magnetic field around it
Describe the construction action of an electromagnet and how the strength of it can be increased
-When current flows in a conductor (wire) it produces a magnetic field around it
-We can work out the way the current goes using the right hand grip rule
We can increase the strength by:
-larger current
-More coils
-Adding an iron core
Describe the Motor Effect
- Current flows in a conductor (wire or coil)
- This creates a magnetic field around the wire which interacts with the permanent magnetic field
- This creates a force (movement) on the wire
- For a motor this creates am upwards force on one side and a downwards force on the other side
- We can find out the direction of the force using Flemings left hand rule
We can use Flemings left hand rule to…
Predict the direction of the resulting force when a wire carries current perpendicular to a permanent magnetic field
What causes there to be no force (movement) during the motor effect
If the current is parallel to the magnetic field
Describe how the strength of the force can be increased
Increasing the current
And in a motor adding more coils
How can the motor effect be used in loudspeakers
- Current flows in the coil
- This creates a magnetic field around the wire, which interacts with the permanent magnetic field
- This creates a force (movement) on the wire
- An AC current is used, so the direction of the force is constantly changing
- This makes the could vibrate (50Hz AC makes the coil vibrate at 50Hz)
- The vibrations cause sound (a longitudinal wave)
Describe how electromagnetic induction creates a voltage in a wire
- A wire (or coil) cuts through magnetic field lines (we can either move the coil, or create a moving magnetic field, but one must move relative to the other)
- This induces a voltage across the wire (if the wire is part of a circuit, this creates a flow of current)
How do we use electromagnetic induction in a power station?
We use electromagnetic induction to generate electricity either by:
-By rotation of a magnet within a coil of wire
or
-Rotation of a coil of wire with a magnetic field
The voltage which is induced through electromagnetic induction can be increased by…
- Moving ht wire relative to the field faster
- Using more coils
- Using a stronger magnetic field
Describe the construction of a transformer
- Two coils are wound around an iron core (or a pair of ‘C’ cores that are held together
- Current in the primary coil creates a magnetic field (the presence of the ironware increases the strength of the field)
- The current must be AC (won’t work with DC)
- The AC current crates a changing magnetic field, which causes the secondary coil to cut field lines (as the field moves)
- This induces a voltage in the secondary coil
Explain why electrical power is transmitted at high voltage and low current
- When large current flows electrons collide with the ions in the metal lattice (that make up the wire)
- The electrons transfer (kinetic) energy to the ions, and the wire heats up
- This means that some of the electrical energy is lost as heat energy
- The larger the current the more energy is lost as heat
What is the effect of AC current on a magnetic field
- Creates a changing magnetic field which causes the secondary coil to cut field lines (as the field moves)
- This induces a voltage in the secondary coil
What different transformers are there
Step-up transformer - increases voltage
Step-down transformer - decreases voltage
What is the equation for the relationship between input (primary) and output (secondary) voltages and the turns trio for a transformer
Vp. =. np
_. _
Vs. ns
What is the equation for the relationship between input and output current and voltage for 100% efficient transformer
Input power = output power
and since P=IxV
Ip x Vp = Is x Vs
