February 13, 2012

6.10 Sketch Magnetic fields

Sketch and recognise magnetic field patterns for a straight wire, a flat circular coil and a solenoid when each is carrying a current

Straight Wire
If you have a straight wire with a current flowing in a known direction, pointing your right-hand thumb in the direction of the current you can find the direction of the magnetic field by looking at the direction your hands curl around the wire.
For example, as in the diagram below, if the current is flowing upwards pointing your thumb upwards reveals that the magnetic field is flowing in a anti-clockwise motion.

Flat circular coil
Using the Right Hand Grip Rule (RHGR) we can predict that a coil of wire will produce a magnetic field similar to that of a small bar magnet.

A cylindrical coil of wire is called a solenoid. Passing a current through a solenoid produces a flux roughly the same shape as a bar magnet. Because of its shape is also produces a uniform magnetic field inside the solenoid.
You can predict the poles of a solenoid by using the graphic shown above. If you are looking at the solenoid from one end and the current is flowing anti-clockwise that end is the North Pole, this means that looking from the other direction the current would flow clockwise producing the South Pole.

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