6.3 Electromagnetism

What is a magnetic field?

a region of space in which moving chartged particles are subject to a magnetic force - magnetic fields can be created by moving charges, the interaction of two magnetic fields results in a magnetic force

What direction do magnetic field lines go?

north to south

What is the magnetic field pattern for a long straight current carrying conductor?

produces concentric circles - right hand grip rule

What is the magnetic field pattern for a flat coil?

similar right hand grip rule and solenoid - fingers are direction of current, thumb is direction of field (to north)

What is the magnetic field pattern for a long solenoid?

similar right hand grip rule and flat coil - fingers are direction of current, thumb is direction of field (to north)

What is the first finger in Fleming’s left hand rule?

direction of magnetic field

What is the second finger in Fleming’s left hand rule?

direction of CONVENTIONAL current

What is the thumb in Fleming’s left hand rule?

direction of force/motion

What is the force on a current-carrying conductor?

F=BIL

Describe an experiment to determine the uniform magnetic flux density between the poles of a magnet

What is magnetic flux density?

magnetic field strength, the amount of magnetic flux per unit area

What is magnetic flux density measured in?

T/Tesla

What happens to charged particles in a uniform magnetic field?

a force acts upon it, use Fleming’s left hand rule to determine direction

What is the circular motion of a charged particle in a uniform magnetic field?

mv²/r =BIL

What is the derivatio of F=BQv?

F=BIL=BQL/t, L/t = v so F=BQv

How does a velocity selector work?

both magnetic and electric forces are charge dependent - put two parallel plates with a voltage perpendicular to a magnetic field, F=EQ, F=BQv, when forces are balanced, v=E/B, which means at this velocity particles will travel in a straight line

What is magnetic flux?

the product of magnetic flux density and the area perpendicular to the lines of flux

What is magnetic flux measured in?

Wb/Weber

What is the force on a charged particle travelling at right angles to a uniform field?

F=BQv

What is magnetic flux linkage?

the sum of magnetic flux through each turn of the coil, product of magnetic flux and number of turns in the coil

What is Faraday’s law of electromagnetic induction?

e.m.f. is proportional to the rate of change of magnetic flux linkage

What is Lenz’s law?

induced e.m.f. is generated in a direction so that it opposes the change that produced it

What is the equation for Faraday’s law?

E=BAN/t

Describe an experiment to investigate magnetic flux

How does an AC generator work?

converts kinetic energy to electrical energy - uses a coil of wire placed in a constant uniform magnetic field, the coil is rotated so the area perpendicular to the magnetic field is constantly changing, so changing magnetic flux linkage induces an alternating current

How do transformers work?

it is an iron core with a primary input coil and a secondary output coil - the ac current in primary coil induces varying magnetic flux in iron core, which induces a current in the secondary coil - change in flux linkage is constant so ratio of number of coils is equal to ratio of e.m.f.

Describe an experiment to investigate transformers