Lecture 19-Wednesday March 11

Magnetic Forces on Moving ChargesMass Spectrometers

Review of Monday

• Field of a long straight wire• Field of a loop• Field of a solenoid

Drawing Field Vectors and Field Lines of a Current-Carrying Wire

Slide 24-21

0( )2

IB r

r

Point P is 5 cm above the wire as you look straight down at it. In which direction is the magnetic field

at P?

A B C D E

20% 20% 20%20%20%

1. A2. B3. C4. D5. E

Checking Understanding

A. 10 A to the right.

B. 5 A to the right.

C. 2.5 A to the right.

D. 10 A to the left.

E. 5 A to the left.

F. 2.5 A to the left.

The magnetic field at point P is zero. What are the magnitude and direction of the current in the lower wire?

Slide 24-27

The Magnetic Field of a Current Loop

Slide 24-23

0

2CENTER OF LOOP

IB

R

The Magnetic Field of a Solenoid

A short solenoid A long solenoid

Slide 24-24

The Magnetic Field Inside a Solenoid

Magnetic field inside a solenoid of length L with N turns.

B0 IN

L

Slide 24-31

Quiz #7

• What is the magnetic field strength and direction at point A?

10 A

10 A

2 cm

2 cmA

The Force on a Charged Particle Moving in a Magnetic Field

Slide 24-32

The Right-Hand Rule for Forces

Slide 24-33

Slide 24-34

Paths of Charged Particles in Magnetic Fields

r mv

qB

Slide 24-35

Charged particle moving perpendicular to uniform magnetic field

• Magnetic force is perpendicular to velocity:

• What path if F ┴ v ?

sinmF qvB qvB

2

Circ

mvF q vB

rmv

rq B

The Mass Spectrometer

Slide 24-36

qBrm

v

Next Monday

• Read: 24: 6—Force on a current carrying wire• Problems: 24: CQ10, MC33, 22, 25, 26, 29, 31,

WB 24: 16-22