Magnetic fields

What is magnetic flux linkage

The product of number of turns and magnetic flux

What is Faraday’s law

Induced emf is directly proportional to the rate of change of flux linkage (constant of proportionality = -1)

What is Lenz’s Law

The direction of the induced emf or current is always such as to oppose the change producing it.

Direction of magnetic field lines

north → south 

How do you show that a magnetic field is strong

Draw the field lines closer together

Right-hand grip rule

Thumb = direction of current, fingers = coil in direction of magnetic field

Fleming’s left-hand rule 

Thumb = F, First finger - B, Middle finger - I 

In a simple transformer, explain how an emf is induced across the ends of the secondary coil.

• There is an alternating magnetic flux

• Magnetic flux within iron core

• Secondary coil is linked by an alternating magnetic flux

Which law indicates that charge is conserved?

Kirchoff’s 1st law

Explain and describe how a uniform magnetic field can be applied in the space between charged plates to select beta-particles with a specific speed. (3 marks)

• Apply a magnetic field perpendicular to the electric field

• Electric force = magnetic force

• No resultant vertical force, so only beta-particles with a specific speed will travel horizontally

Describe how a student could do an experiment in the laboratory to show that the max emf induced in the secondary coil is directly proportional to the number of turns on the secondary coil. (3 marks)

• connect primary coil to an alternating current

• connect an oscilloscope across the secondary coil to measure E

• a graph of E against N will be a straight line through the origin