⚛️ Physics Quiz 19: Magnetic Forces and Fields

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⚛️ Physics · Quiz 019

Introduce magnetic fields as forces on moving charge and current, using current from PHYS-018 and circular-motion ideas from PHYS-007.

Learning goalDetermine magnetic-force magnitudes and directions and connect perpendicular magnetic force to circular charged-particle motion.

  • 5 questions
  • Foundation
  • Explanations after finishing
Answered 0/5
FoundationA charged particle is instantaneously at rest in a magnetic field, with no electric field present. What magnetic force acts on it?
Need a small nudge?

Use the speed dependence in F = |q|vB sin theta.

UnderstandingA positive charged particle moves in a uniform magnetic field with velocity exactly perpendicular to the field. If only the magnetic force acts, what happens to the particle's speed?
Need a small nudge?

Compare the direction of magnetic force with the instantaneous velocity.

ApplicationA positive charge of 2.0 microC moves at 3.0 x 10^4 m/s perpendicular to a uniform 0.20 T magnetic field. What is the magnetic-force magnitude?
Need a small nudge?

For perpendicular motion, sin theta = 1, so F = |q|vB.

InterpretationA straight 0.40 m wire carries 5.0 A east through a uniform 0.30 T magnetic field directed north. The wire and field are horizontal and perpendicular. What magnetic force acts on the wire?
Need a small nudge?

First calculate F = ILB. Then use the right-hand rule for current east crossed with field north.

ConnectionA positive ion of mass 2.0 x 10^-26 kg and charge 1.6 x 10^-19 C enters a uniform 0.50 T magnetic field at 4.0 x 10^5 m/s perpendicular to the field. If no other forces matter, which statement is correct?
Need a small nudge?

Set magnetic force qvB equal to centripetal force mv^2/r, then interpret the work done by the magnetic force.

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