Peoples Physics Concepts

14.5. Generators and Motors http://www.ck12.org

Example 2

To create a simple generator, you are holding a single coil of wire in place on a table. You hold a bar magnet
directly above the center of the wire and move it toward the wire and away from the wire repeatedly to create a
current in loop. (a) As you bring the bar magnet toward the loop, which direction does the current flow? (b) As you
move the magnet away from the loop, which direction does the current flow?

Solution

(a): As you bring the magnet closer to the loop, the magnetic field will increase in strength thus increasing the

magnetic flux going into the table through the loop. In order to oppose this change in flux, the induced current will

need to create a magnetic field that will point out of the table through the loop. We can use the first right hand rule,

starting with the direction of them magnetic field instead of the direction of the current, to determine that the

current will need to move in the CCW direction.

(b): When you move the magnet away from the loop, the magnetic field will be decreasing thus decreasing the

magnetic flux going into the table through the loop. The induced current will need to create a magnetic field that is

also pointed into the table through the loop to oppose this change in flux. Again, we use the second right hand rule

to find that the current must go in the CW direction.

Watch this Explanation

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/323

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/3632