Chapter 23 - Magnetic Fields Flashcards
(15 cards)
What do the arrows on a magnetic field line represent?
The direction that a free north pole would move (from north to south).
How can you determine the magnetic field lines around a wire?
Using the right hand grip rule, where the thumb represents the flow of current and fingers represent the field lines.
How can you determine the magnetic field lines around a flat coil or solenoid?
Using the right hand grip rule, where the fingers represent the flow of current and the thumb represents the field lines.
What does each finger represent in Flemming’s left hand rule?
Thumb - Direction of motion.
Forefinger - Direction of magnetic field.
Middle finger - Direction of current.
What is magnetic flux density?
A measure of the strength of a magnetic field, can be thought of as field lines per unit area.
What is magnetic flux?
The product of flux density and cross sectional area, it can be thought of as the number of field lines.
What is magnetic flux linkage?
The product of the number of turns in a coil and its magnetic flux.
Outline an experiment to determine magnetic flux density between two poles.
-Place the two poles on a top pan balance with a wire between them.
-Record the change in the mass reading when current is passed through the wire.
-Find F using F = mg
-Find flux density using B = F/IL
Describe the movement of a charged particle in a magnetic field.
The force acting on the particle remains constant, but changes direction as the particle changes direction. This causes it to undergo circular motion.
What is a velocity selector?
A device that uses both electric & magnetic fields to exert a force on moving particles. Only particles with a specific velocity will have the correct resultant force for it to pass through a narrow slit.
State Faraday’s Law.
The induced e.m.f. is directly proportional to the rate of change of flux linkage.
State Lenz’s Law.
The induced e.m.f. in a wire is always in such a direction as to oppose the charge that caused it.
Outline an experiment to demonstrate Faraday’s Law.
-Place a search coil between two bar magnets.
-Measure the P.D. across the coil at very short time intervals (use a data reader).
-Immediately move the coil out of the field, keeping its orientation the same.
-Plot a graph of e.m.f. against time.
Describe a simple A.C. generator.
-A coil rotates inside a magnetic field, generating a current.
-Slip rings and brushes are used to connect the current to a circuit.
-Output voltage changes direction with every half turn.
Describe a laminated iron core transformer.
-Two coils are wrapped around an iron core, opposite each other.
-When a current passes through the primary coil, it induces a current in the opposite coil.
-The difference in the number of coils will affect the difference in current.
