Moving Charges in Magnetic Fields
chapter 12
lesson 3
Objective
you will be able to;
· use the third left hand rule
· calculate the magnitude and direction
of magnetic force.
What happens when a moving charge enters a
fixed magnetic field?
We must consider the magnetic field around
the moving charge and the fixed field.
Third Left Hand Rule
Whenever two magnetic fields interact, a magnetic
force is created. The direction of the force can be
predicted using this rule.
Direction of Moving Charge
Direction of fixed B
Direction of the force on the
moving charge.
Example
A proton moving to the right enters a magnetic
field that is directed to the top of the page.
Which direction will the proton be deflected?
Formula
The magnitude of the magnetic force (Fm) is given by
the formula;
Fm=Bqv
B is measured in Teslas (T).
q measured in Coulombs (C)
v measured in m/s
Example
An electron crosses a magnetic field at a right angle,
with a speed of 2.00 x 105 m/s , towards the bottom of
the page. The magnetic field is 3.00 x 10-4 T to the
right. Calculate the deflecting force.
Example
A alpha particle is traveling at 2.00 x 106 m/s into the
page, perpendicular to a magnetic field. It is acted
upon by a force of 3.20 x 10-13N, towards the top of
the page. Determine the direction and magnitude of
the magnetic field.
This is what happens when the charged
particle does not enter the fixed field at a
right angle?
Why is the path this shape?
Example
There is a 1.00 x 10-3 T magnetic field to the
right. A proton enters the field at an angle of
30.0° to the field with a speed of 1.00 x 106 m/s
towards the top of the page. What is the
magnetic force acting on the proton?
Assignment
Read text pages 593-601
SNAP p.120 #1,3-7
Text p. 601 #3,5,6
Answers to even
4: 1.30 x 10-13 N, [W]
6: 1.6 T [W]