Moving Charges and Magnetism — Practice

Question 1

A long straight wire carries a current of 10 A. Find the magnetic field at a perpendicular distance of 20 cm from it.

Accepted Answer

Apply B = mu_0 I/(2 pi a), converting the distance to metres first. Answer: B = 1.0 x 10^-5 T.

Question 2

A circular coil of 50 turns and radius 10 cm carries a current of 2.0 A. Find the field at its centre.

Accepted Answer

Use B = mu_0 N I/(2R), since the centre is the x = 0 case of the axial formula. Answer: B = 6.3 x 10^-4 T.

Question 3

A solenoid 50 cm long has 500 turns and carries 3.0 A. Find the field inside it.

Accepted Answer

First convert to turns per unit length, n = 500/0.5 = 1000 per metre, so B = mu_0 n I. Answer: B = 3.8 x 10^-3 T.

Question 4

A proton of speed 2.0 x 10^6 m/s enters a field of 0.50 T perpendicular to it. Find the radius of its path and its frequency.

Accepted Answer

Use r = mv/(qB) and nu = qB/(2 pi m), noting that the frequency does not depend on the speed. Answer: r = 4.2 x 10^-2 m; nu = 7.6 x 10^6 Hz.

Question 5

A wire of length 25 cm carrying 4.0 A is placed at 30 degrees to a field of 0.30 T. Find the force on it.

Accepted Answer

Apply F = BIl sin(theta) with the angle measured between the wire and the field. Answer: F = 0.15 N.

Question 6

Two long parallel wires 10 cm apart carry 5.0 A and 8.0 A in opposite directions. Find the force per metre and say whether it is attractive or repulsive.

Accepted Answer

Use F/l = mu_0 I1 I2/(2 pi d), then apply the direction rule for antiparallel currents. Answer: F/l = 8.0 x 10^-5 N/m, repulsive.

Question 7

A rectangular coil of 100 turns and area 2.0 x 10^-2 m squared carries 1.5 A in a field of 0.25 T. Find the torque when the plane of the coil is parallel to the field, and when it is perpendicular.

Accepted Answer

Use torque = N I A B sin(theta) with theta measured from the normal, so a plane parallel to B means theta = 90 degrees. Answer: 0.75 N m when parallel; zero when perpendicular.

Question 8

A galvanometer has 40 turns, area 1.8 x 10^-3 m squared, field 0.25 T and spring constant 1.0 x 10^-6 N m per radian, with resistance 20 ohm. Find its current and voltage sensitivities.

Accepted Answer

Current sensitivity is NAB/k and voltage sensitivity divides that by the resistance R. Answer: Current sensitivity 18 rad/A; voltage sensitivity 0.9 rad/V.

Question 9

A long straight wire of radius 2.0 mm carries 8.0 A uniformly across its cross-section. Find the field at 1.0 mm from the axis.

Accepted Answer

Choose a circular Amperian loop inside the wire, so the enclosed current is only the fraction of the area it contains. Answer: B = 4.0 x 10^-4 T.

Practice — Moving Charges and Magnetism

Sign in to save attempts to your dashboard and track your accuracy over time

Find a verified tutor

Join a live course

Browse coaching centres

About

Categories

Support

Documentation

Get Study Tips & Updates

Download Our App

Download for iOS

Download for Android

Popular Cities