Let's make some observations of a coil near a magnet. The coil is connected to a sensitive ammeter to measure the direction and size of any current flowing in the coil.

1. See what happens when the north pole of a bar magnet is moved toward a coil from one side.
   
   
2. What happens when the magnet is near the coil but stationary?
   
   
3. What if we take the magnet away, or turn it around?
   
   
4. What if we repeat the experiment at the other end of the coil?
   
   

What do you think happens if the complete circuit, consisting of the meter, two wires, and a coil, is broken by removing one of the wires? Will there still be a current in the coil when we move the magnet relative to the coil?

1. Yes, there will be a current
2. No, there's no current but there will be a potential difference
3. No there's no current, and no potential difference either

Because there is not a complete circuit there will be no current. However, moving the magnet relative to the coil still produces a voltage.

One conclusion we should be able to draw from all this is that exposing a coil to a changing magnetic field generates a voltage in the coil. The coil and meter make up a circuit with a particular resistance, and that determines the magnitude of the current in the circuit.

What happens when you change the orientation of a coil relative to a magnetic field? You can do this either by rotating the coil in the field, or rotating the field. Any change in the relative orientation of the coil and field results in a voltage in the coil.

Another way to induce an emf in a coil is to change the area of the coil. This gives us three ways to generate an emf in a coil or loop:

• change the magnetic field
• change the area
• change the orientation of the coil relative to the field

Wouldn't it be a good idea to define a quantity that includes all of these factors?