20150227080251chp 4 magnetism

8/9/2019 20150227080251Chp 4 Magnetism

1/30

Magnetism

By

ROSZAIRI HARONM.Sc. (Mal), B.Sc. (Hons.) (Mal)

8/9/2019 20150227080251Chp 4 Magnetism

2/30

Magnetic Fields

The needle of a compass is permanent magnet that has a northmagnetic pole (N) at one end and a south magnetic pole (S) at

the other.

8/9/2019 20150227080251Chp 4 Magnetism

3/30

The behavior of magnetic

poles is similar to that of

like and unlike electric charges.

Magnetic Fields

8/9/2019 20150227080251Chp 4 Magnetism

4/30

Surrounding a magnet there is a magnetic f ie ld . The direction

of the magnetic field at any point in space is the direction indicated

by the north pole of a small compass needle placed at that point.

Magnetic Fields

8/9/2019 20150227080251Chp 4 Magnetism

5/30

The magnetic field lines and pattern of iron filings in the vicinity of a

bar magnet and the magnetic field lines in the gap of a horseshoemagnet.

Magnetic Fields

8/9/2019 20150227080251Chp 4 Magnetism

6/30

Magnetic Fields

8/9/2019 20150227080251Chp 4 Magnetism

7/30

When a charge is placed in an electric field, it experiences a

force, according to

EF

q

The Forc e That a Magnetic Field Exerts on a Charge

8/9/2019 20150227080251Chp 4 Magnetism

8/30

The following conditions must be met for a charge to experience

a magnetic force when placed in a magnetic field:

1. The charge must be moving.

2. The velocity of the charge must have a component that is

perpendicular to the direction of the magnetic field.


8/9/2019 20150227080251Chp 4 Magnetism

9/30

Righ t Hand Rule No. 1 . Extend the right hand so the fingers point

along the direction of the magnetic field and the thumb points along

the velocity of the charge. The palm of the hand then faces in the

direction of the magnetic force that acts on a positive charge.

If the moving charge is negative,

the direction of the force is oppositeto that predicted by RHR-1.


8/9/2019 20150227080251Chp 4 Magnetism

10/30

DEFINITION OF THE MAGNETIC FIELD

The magnitude of the magnetic field at any point in space is defined

as

sinvq F

Bo

where the angle (0

8/9/2019 20150227080251Chp 4 Magnetism

11/30

Example 1 Magnetic Forces on Charged Particles

A proton in a particle accelerator has a speed of 5.0x106 m/s. The proton

encounters a magnetic field whose magnitude is 0.40 T and whose direction

makes and angle of 30.0 degrees with respect to the proton’s velocity

(see part (c) of the figure). Find (a) the magnitude and direction of the

force on the proton and (b) the acceleration of the proton. (c) What wouldbe the force and acceleration of the particle were an electron?


8/9/2019 20150227080251Chp 4 Magnetism

12/30

N106.1

0.30sinT40.0sm100.5C1060.1sin

13

619

vBq F o(a)

(b)

(c)

213

27

13

p

sm106.9kg1067.1

N106.1

m

F a

Magnitude is the same, but direction is opposite.

217

31

13

e

sm108.1kg1011.9

N106.1

m

F a


8/9/2019 20150227080251Chp 4 Magnetism

13/30

8/9/2019 20150227080251Chp 4 Magnetism

14/30

The magnetic force on the

moving charges pushes the

wire to the right.

The Forc e on a Current in a Magnetic Field

8/9/2019 20150227080251Chp 4 Magnetism

15/30

sinqvB F

sin Bt vt

q F

L

I

sin ILB F


8/9/2019 20150227080251Chp 4 Magnetism

16/30

Example 5 The Force and Acceleration in a Loudspeaker

The voice coil of a speaker has a diameter of 0.0025 m, contains 55 turns of

wire, and is placed in a 0.10 T magnetic field. The current in the voice coil is

2.0 A. (a) Determine the magnetic force that acts on the coil and the

cone. (b) The voice coil and cone have a combined mass of 0.0200 kg. Find

their acceleration.


8/9/2019 20150227080251Chp 4 Magnetism

17/30

(a)

N86.0

90sinT10.0m0025.055A0.2

sin

ILB F

(b)2sm43

kg020.0

N86.0

m

F a


8/9/2019 20150227080251Chp 4 Magnetism

18/30


8/9/2019 20150227080251Chp 4 Magnetism

19/30

Righ t-Hand Ru le No. 2 . Curl the fingers of the

right hand into the shape of a half-circle. Pointthe thumb in the direction of the conventional

current, and the tips of the fingers will point

in the direction of the magnetic field.

Magnet ic Fields Prod uced by Currents

8/9/2019 20150227080251Chp 4 Magnetism

20/30

A LONG, STRAIGHT WIRE

r

I B

o

2

AmT104 7 o

permeability of

free space


8/9/2019 20150227080251Chp 4 Magnetism

21/30

Example 7 A Current Exerts a Magnetic Force on a Moving Charge

The long straight wire carries a current

of 3.0 A. A particle has a charge of

+6.5x10-6 C and is moving parallel to

the wire at a distance of 0.050 m. The

speed of the particle is 280 m/s.

Determine the magnitude and direction

of the magnetic force on the particle.


8/9/2019 20150227080251Chp 4 Magnetism

22/30

sin2

sin

r

I qvqvB F o

r

I B

o

2


8/9/2019 20150227080251Chp 4 Magnetism

23/30

Current carrying wires can exert forces on each other.


8/9/2019 20150227080251Chp 4 Magnetism

24/30

Conceptual Examp le 9 The Net Force That a Current-Carrying Wire

Exerts on a Current Carrying Coil

Is the coil attracted to, or repelled by the wire?


8/9/2019 20150227080251Chp 4 Magnetism

25/30

A LOOP OF WIRE

center of circular loop

R

I B o

2


8/9/2019 20150227080251Chp 4 Magnetism

26/30

Example 10 Finding the Net Magnetic Field

A long straight wire carries a current of 8.0 A and a circular loop of

wire carries a current of 2.0 A and has a radius of 0.030 m. Find the

magnitude and direction of the magnetic field at the center of the loop.


8/9/2019 20150227080251Chp 4 Magnetism

27/30

R

I

r

I

R

I

r

I

B

ooo 2121

222

T101.1m030.0

A0.2

m030.0

A0.8

2

AmT104 57

B


8/9/2019 20150227080251Chp 4 Magnetism

28/30

The field lines around the bar magnet resemble those around the loop.


8/9/2019 20150227080251Chp 4 Magnetism

29/30


8/9/2019 20150227080251Chp 4 Magnetism

30/30

A SOLENOID

Inter ior of a solenoid nI B o

number of turns per

unit length


20150227080251chp 4 magnetism

Documents