What is the friction force between the rails and the crossbar?  A metal crossbar slides on a pair of conducting rails separated by a distance L = 0.35 m and connected to a battery that provides a current of 3 A. A magnetic field B = 1.2 T is established perpendicular to the crossbar and the rails. The crossbar moves at a constant velocity along the rails.

Expert Answers

An illustration of the letter 'A' in a speech bubbles

When a current flows through a wire that is placed in a magnetic field there is a force created due to the interaction of the field and the charges flowing through the wire.

The magnitude of this force is given by F = I*L*B where I is the current flowing through the wire, L is the length of the wire and B is the magnetic field.

In the problem, the length of the metal cross bar is 0.35 m, the current flowing through it is 3 A and a magnetic field of 1.2 T acts perpendicular to the cross bar and the rails. This results in a force along the rails equal to F = 3*0.35*1.2 = 1.26 N

But the crossbar moves at a constant velocity in spite of the force. This is due to frictional force between the crossbar and the rails that is equal to the force acting on it. The frictional force between the rails and the crossbar is 1.26 N.

Approved by eNotes Editorial Team
Soaring plane image

We’ll help your grades soar

Start your 48-hour free trial and unlock all the summaries, Q&A, and analyses you need to get better grades now.

  • 30,000+ book summaries
  • 20% study tools discount
  • Ad-free content
  • PDF downloads
  • 300,000+ answers
  • 5-star customer support
Start your 48-Hour Free Trial