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MINI QUIZ TO CHECK YOUR UNDERSTANDING

I. EXPLANATION  
· What is a magnetic field?

· What are magnets?

· How is magnetism used?

II. MULTIPLE CHOICE
1. What does the movement of an electric charge cause?
The movement of a magnetic charge (a)

An electron or proton (b)

A magnetic field (c)

2. What happens when two objects with magnetic fields are brought near each other?
A magnetic force either causes attraction or repulsion (a)

A magnetic force will cause electrical charges (b)

The objects will become magnets (c)

3. Is a magnet a dipole or monopole?

Monopole, because it is one magnet (a)

Dipole, because it has two poles (b)

It depends if the poles are like or different (c)

III. PROBLEM

1) Four wires are arranged into a rectangle; the short sides are 1.7 m in length, and the long sides are 8.1 m in length. A current of 7.9 A is passed through the pieces of wire, making it effectively a current loop. A magnetic field of 7.8 μT is established in the plane of the rectangle, parallel to the short sides. The magnitude of the net force on all the wires in the rectangle is ______ N.

Answer to Problem

Use F=il x B.

Because (the current in) the short wires are parallel to B, the force on the short wires is zero, and they can be ignored.

Also, the currents in the long sides is of equal magnitude and in opposite directions, so the force on one side is equal and opposite to the force on the other side and they cancel.

Thus the net force is zero.

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