Electromagnetism Flashcards
What are permanent magnets?
These hold their magnetism over a long period and are usually made from steel or the alloy alnico
What are electromagnets? (temporary magnets)
Frequently made from soft iron which does not retain its properites
What do unlike poles do?
Attract i.e. North and South
What do like poles do?
Repel i.e. south and south, north and north
What are the field line rules?
Never cross over
Arrow is from N to S
Closer = more intense field
They are continuous lines
What is a magnetic field represented by?
Magnetic flux lines
How does an electric current create a magnetic field?
When an electric current flows through a conductor there is a magnetic field created around it
What happens to a magnetic field when a current is reversed?
Magnetic field is reversed
What does the right hand grip rule state?
If the fingers of the right hand wrap around the coil in the direction of the current. The thumb will point to the north end.
What does an electromagnet consist of?
Insulated wire around a soft iron core. The wire is insulated so that the nail doesn’t become the circuit
What factors affect the strength of an electromagnet?
Increasing the number of coils
Increasing the current
Adding an iron core
What is the force always of a magnetic field when a conductor is placed in it?
At right angles or perpendicular to the field and current direction
Is largest when the field and current directions are at right angles to each other
What happens to the force when either field or current direction is reversed?
The direction of motion also reverses
What is Flemings left hand rule?
If the current and field directions are not at right angles to each other then the force is smaller and if the current and field directions are parallel the force is zero
What does a galvanometer read after a wire has been moved down through a magnetic field? (Experiment 1)
Deflects rights then zero (left if up)
What can you notice about the current in a galvanometer?
It is registered in the meter when there’s relative movement between the wire and the magnetic field. Current is induced in the wire by the process of electromagnetic induction
What is the current size dependent on in a galvanometer?
Speed of wire motion
What happens on a galvanometer when you move the N pole towards the coil? (Experiment 2)
Deflects left then zero (right for south pole)
Factors about electromagnetic induction?
Most be relative movement between magnet and coil for current to be induced.
Faster movement produces larger induced currents
More coils produce larger induced current
Reversing the motion or the poles of magnet reverses the induced current direction
What happens to the current when the switch is closed? (Experiment 3)
It begins to flow through coil A and builds a magnetic field. This field links coil B and the meter registers a current pulse. Once the field has reached full strength the meter reads zero. Opening the switch the field will die away and the meter registers a pulse in the opposite direction
What happens when the coils are linked with an iron core? (Experiment 3)
The current pulse is much larger. Because the iron core creates a much stronger magnetic field and concentrates it along the axis of the coils
What are transformers?
Used to change the voltage of an ac supply.
What happens in a transformer?
Alternating current flows in primary coil and creates a field in the iron core that is continually changing direction. This induces an ac current in the secondary coil
Transformer equation
Ns Vs
=
Np Vp
