AH 2.1.2 Magnetic Fields and Magnetic Induction

Question 1

Explain the concept of a magnetic field

Answer 1

A magnetic field is the region in space in which a moving charge will experience a force.

Question 2

Copy and complete this statement.

Iron, nickel, cobalt, and some rare earth elements exhibit a magnetic effect called …………………………………., in which magnetic …………………… can be made to …………….., resulting in the material becoming magnetised. This is the reason ……………………. magnets have magnetic fields around them.

Answer 2

Iron, nickel, cobalt, and some rare earth elements exhibit a magnetic effect called ferromagnetism, in which magnetic dipoles can be made to align, resulting in the material becoming magnetised. This is the reason permanent magnets have magnetic fields around them.

Question 3

What equation gives the Lorentz Force on a wire of length l carrying a current I at angle θ to the magnetic field lines inside a magnetic induction B as shown below.

Answer 3

F = B I l sinθ

Question 4

Sketch the magentic field lines which show the magnetic induction around the straight current-carrying wire shown below and explain the mnemonic used to remember their direction.

Answer 4

Question 5

State the equation which gives the magentic induction B at a perpendicular distance r from a straight wire carrying current I.

Specify the meaning and unit of each term in the equation and the value of any physical constants.

Answer 5

B = μ_oI/2πr

B = Magnetic Inducton (Teslas, T)

I = current in wire (A)

r = perpendicular distance from wire to point in question (m)

μ_o = the permeability of free space = 4π x 10^-7 T m A^-1

(sometimes called the magnetic constant)

Question 6

Sketch the magentic filed pattern around a coil of current-carrying wire.

Answer 6

Magnetic field lines always flow from the NORTH pole to the SOUTH pole of the magnet.

So, in the diagram below, the NORTH pole is at the left end of the coil and the SOUTH pole is at the right end.

Question 7

Is there a difference between Magnetic Field Strength and Magnetic Induction?

Answer 7

No! Magnetic Field Strength and Magnetic Inducton mean the same thing.

Question 8

Define Magnetic Induction

a) in words
b) by referring to an equation., making reference to it’s unit.

Answer 8

A magnetic induction (field strength) B of one Tesla is present when a current of one Amp flowing in a wire of length one metre within the magnetic field feels a force of one Newton

This follows from the equation

F = B I l sinθ where θ = 90^o, so

F = B I l , so

B = F/ I l

F = Lorentz Force on wire (N)

B = Magnetic Induction (Field strength) (T)

I = current flowing in wire (A)

l = length if wire in magentic field (m)

So 1 Tesla = 1 Newton per Amp-metre

1 T = 1 N A^-1 m^-1