Magnetism

Magnetic field- A magnet creates a

magnetic field in its vicinity.

Magnetism

It represents the effect a magnet has on its surroundings.

Magnetism

All magnetic fields arise from the motion of electric charge.

MagnetismMagnetic field lines can be used to represent magnetic fields.The closer the lines are together, the greater the magnitude of the vector B

Figure 22-4 Magnetic Field Lines for a Bar Magnet

Magnetism

A magnetic field is represented by the symbol B

MagnetismThe direction of a magnetic field at a given location is the direction

in which the north pole of a compass points when it is placed in

that location.

B

MagnetismA charged particle moving in a

magnetic field will experience a force if it has a velocity component

perpendicular to the magnetic field.

Magnitude of the magnetic force F

sinF q vB

Magnetism

Magnitude of the magnetic field B

1N SI unit = 1 tesla=1 T=

sin A•m

FB

q v

MagnetismThe Magnetic Force Right

Hand Rule (RHR)

MagnetismTo find the direction of the magnetic force F,

point your fingers in the direction of the velocity v.

Now curl them toward the direction of B.

Your thumb points in the direction of F.

Figure 22-8The Magnetic Force

Right-Hand Rule

Figure 22-9The Magnetic Force for Positive and Negative Charges

Conceptual Checkpoint 22-2Which is the positive? Negative? Zero charge?

MagnetismVelocity selector.

A device with both magnetic and electric fields present. Only charged particles moving with a certain speed will pass through undeflected.

Magnetism

The velocity that is undeflected is calculated by

E v=

B

Conceptual Checkpoint 22-3Which direction should the magnetic field be

to give zero force?

MagnetismA charged particle moving with a

velocity perpendicular to a uniform magnetic field, will move in a circle.

Figure 22-11The Electromagnetic Flowmeter

Magnetism

2 2

Recall

a Fcp cp

v mv

r r

Magnetism

2mvq vB=

r

Magnetism

mvr =

q B

Figure 22-12Circular Motion in a Magnetic Field

Example 22-3Uranium Separation

•Forces on a long straight current carrying wire in a magnetic field.

Magnetism

•Forces on a long straight current carrying wire in a magnetic field.

Magnetism

•A long straight current carrying wire has charges moving inside it.

Magnetism

•If it is placed in a magnetic field, it will experience a force

Magnetism

MagnetismThe magnitude of the force is

F = ILBsin

Where F is the magnitude of the force

B is the magnitude of the magnetic field

Magnetism

L is the length of the wire in the magnetic field

is the angle between the direction of the

magnetic field vector,

and the direction of the current.

Figure 22-15The Magnetic Force on a

Current-Carrying Wire

Direction of magnetic forces in a current carrying loop in a

magnetic field.

Magnetism

Figure 22-16Magnetic Forces on a Current Loop

Example 22-5Torque on a Coil

MagnetismThe magnitude of the torque is

= IABsin

Where is the torque

B is the magnitude of the magnetic field

A is the area of the loop

MagnetismFor a loop of N turns,

= NIABsin

Where is the torque

B is the magnitude of the magnetic field

A is the area of the loop

•To calculate the magnitude and direction of the magnetic field in the

vicinity of a long straight current carrying wire.

Magnetism

Apply the magnetic field right hand rule.1. Point your thumb in the direction of

current flow.2. Curl your fingers around the wire 3. They will point in the direction of

the magnetic field.

Magnetism

Figure 22-19The Magnetic Field

of a Current-Carrying Wire

Magnetism

7

2 permeability of free space =

4 10

o

o

IB

r

T m

A

Magnetism