Chapter 22
1.
Picture the Problem:
A proton moves in a magnetic field that is directed at right angles to its velocity.
Strategy:
Combine Newton's Second Law with the magnetic force (equation 221) to find the
acceleration of the particle.
Solution:
Set the magnetic force equal to the
mass multiplied by the acceleration and
solve for
a
:
Insight:
If the magnetic field were parallel to the velocity, the angle
θ
=
0° and the force and
acceleration would be zero.
8.
Picture the Problem:
An electron moves in a region in which a magnetic field exists.
Strategy:
The ion experiences no magnetic force when it is moving in the
direction, so we conclude
that the magnetic field also points along either the
direction. We can use either the LeftHand
Rule for negative charges, or use the RightHand Rule and remember to reverse the direction of the
force because the charge on the electron is negative. Try pointing your left thumb downwards (
direction) and the fingers of your left hand in the
direction to find that the magnetic field must point
in the
direction. Then use equation 221 and the force experienced by the electron when it moves in
the
direction to find the magnitude of
Solution:
Use equation 221 to
find
Insight:
If instead the electron were to travel in the
direction, it would experience a force
9.
Picture the Problem:
Two charged particles travel in a magnetic field along the same direction and
experience the same magnetic force, but they travel at different speeds.
Strategy:
Use equation 221 to calculate the ratio of the speeds of the particles.
Solution:
1. (a)
Since the magnetic force is directly proportional to both the charge and the speed of
the particles, and since the particles experience the same force, particle 2 must have a greater speed
because particle 1 has the greater charge.
2.
(b)
Use equation 221 to find the ratio:
Insight:
Suppose both charges were allowed to travel in circles as described in section 223.
Assuming both charges have the same mass, we find that
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 Spring '08
 Dr.G
 Physics, Acceleration, Force, Magnetic Field, 0°, Electric charge, 2.0 mm

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