Moving Charges and Magnetism Test

Result

Moving Charges and Magnetism Test - 4

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Weekly Quiz Competition

Question 1
1 / -0

A loop of irregular shape carrying current is located in an external magnetic field. If the wire is flexible, why does it change to a circular shape?

A
for a given perimeter, circle encloses greater area than any other shape.

B
to maximize the total amount of flux passing through it.

C
both A and B

D
the torque acting on the loop exerts a force in the outward direction, extending it into a circular shape.

Solution

It assumes circular shape with its plane normal to the field to maximize flux, since for a given perimeter, a circle encloses greater area than any other shape.
Question 2
1 / -0

A 100 turn closely wound circular coil of radius 10 cm carries a current of 3.2 A. A uniform magnetic field of 2T in the horizontal direction exists such that initially the axis of the coil is in the direction of the field. The coil rotates through an angle of 90º under the influence of the magnetic field. What are the magnitudes of the torques on the coil in the initial and final position respectively?

A
zero, zero

B
16 Nm, zero

C
zero, 20 Nm

D
6Nm, 20 Nm

Solution

The torque exerted on a current loop is expressed as,

τ = |m× B| = m B sin(θ)

Initially, θ = 0. Thus, initial torque τ_i = 0.

Finally, θ = π/2 (or 90º). Thus, final torque τ_f = m B = 10 × 2 = 20 N m.