Transcript Force on a Charged Particle

Bellwork
A wire carrying a current of 3.0 A is in a uniform
magnetic field. The wire makes an angle of 15°
with the field. The wire is 35 cm in length and the
force on the wire is 0.80 N. What is the strength of
the magnetic field?
Force on a Charged Particle
• Charged particles are not confined to a wire.
• Cathode-ray tube in monitors and TVs use magnetic
fields to deflect electrons to form pictures on the
screen.
• The screen in coated with phosphor to glow when an
electron hits it.
• The force produced by a magnetic field on a charged
particle depends on it’s velocity, it’s charge (+/-),
and on the strength of the field.
• Direction of force is perpendicular to both the
velocity of the particle and the B-field.
• F= Bqv
• B- magnetic field (T)
• q- charge of particle (C) (no negatives)
• v- velocity of particle (m/s)
To determine directions:
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Use the 2nd RHR:
Thumb point in the direction of the velocity
Fingers faces the direction of the field
Your palm points to the direction of the force on a
POSITIVE particle. It will be opposite for a
NEGATIVE particle.
Practice
• A proton travels at 3.0 x 106 m/s to the west through
a uniform magnetic field of 0.04 T toward the north.
What is the force on the proton?
• An electron travels at 2.7 x 105 m/s to the west
through a uniform magnetic field of 0.07 T toward
the north. What is the force on the electron?
Review
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1st RHR
Magnetic Field Lines
F = BIL
2nd RHR
F = Bqv
3rd RHR