Magnetic Currents

Magnetic Force on Current-Carrying Wire

By Rachel Wampler

Magnetic Force on a Curent-Carrying Wire

Speakers

• Speakers are coils of wire attached to a cone

• They are enclosed by a magnet

• Avarying current is run through the wire

• The current in the B-field makes the speaker cone move back and forth​

Magnetohydrodynamic Propulsion

Multiple Choice

A 2 m wire is in a 2x10^-6 T magnetic field pointing into the page. It carries 2 A of current flowing up. What is the force on the wire?

• 2x10^-6 N, Left

• 8x10^-6 N, Left

• 2x10^-6 N, Left

• 8x10^-6 N, Right

Looped Wire in B-field

• What happens when you put a loop of wire in a magnetic field?

• Side 1 is forced up and side 2 is ​forced down(RHR)

• These rotating forces produce a torque

• The loop then turns until its normal is aligned with the B-field

  • The normal is perpendicular to the plane of the loop​

Torque on a Loop of Wire

Electric Motor

• Many loops of current carrying wire placed between two magnets

• The loops are attached to half-rings

• The torque turns the loops until the normal is aligned to the B-field

• At that point the half-rings don't connect to electric current

• Momentum makes the loop turn more

• The half-rings connect with the current to repeat the process​

Multiple Choice

A simple electric motor needs to supply a maximum torque of 10 Nm. It uses 0.1 A of current. The magnetic field in the motor is 0.02 T. If the coil is a circle with radius of 2 cm, how many turns should be in the coil?

• 9.56x10⁶ Turns

• 1.57x10⁶ Turns

• 3.98x10⁶ Turns

• 2.51x10⁶ Turns