Download magnetic fields - King`s Senior Science

What is the direction of this force?
Just use the right hand slap rule…
 Fingers point in the direction of the magnetic
field (B)
 Forward slap is the force acting on a (+ve)
charge
 Back hand slap is force acting on a (-ve)
charge eg for electrons
 Thumb is direction of charge (velocity vector)
In the following examples, is the charge + or - ?
x
x
x
x
?
x
x
x
x
x
x
x
x
x
x
x
x
?
?
Determine the magnitude and direction of the force
on an electron traveling horizontally to the east in
an outward magnetic field of strength 0.75 T.
V = 8750 ms-1
north
Direction?
east
FM  qvB



FM  1.6 x 1019 C 8.75 x 103 m/s 0.75T 
FM  1.05 x 10
15
N
When the charge moves
perpendicular to the B-field,
we can show that:
F  qvB
mv 2
qvB 
r
qrB  mv
2
v2
v
a
F  m
r
r
-
An electron in a magnetic field moves at a speed
of 1.3 x 106 m/s in a circle of radius .35 m. Find
the magnitude and direction of the magnetic field.
Electron mass 9.11 x 10-31 kg
q electron 1.60 x 10-19 C
B
-
v
x
x
x
x
x
x
x
x
x
x
E
As the electron enters the crossed fields:
The Electric Field deflects it in what direction?
The Magnetic Field deflects it in what direction?
If E and B are adjusted so that the electron continues
in a straight line…
E
v
B
What is the velocity of a beam of
electrons that go undeflected when
passing through perpendicular electric
and magnetic fields of magnitude 8.8
x 103 V/m and 3.5 x 10-3 T,
respectively? What is the radius of the
electron orbit if the electric field is turned off?
FE  FM
qE  qvB
E 8.8 x 103 V/m
v 
B 3.5 x 10 3 T
v  2.5 x 106 m/s
mv 2
FM  qvB 
r
mv
r
qB
FE
v
FM

9.11 x 10  31 kg 2.5 x 106 m/s 

1.6 x 1019 C3.5 x 10 3 T
r  4.1 x 10 3 m