Question

magnetic field at the centre of a coil carrying current in clock wise direction is
a. towards the centre of the coil
b. away from the centre of the coil
c. towards you
d . away from you

Answer 1

10.2 Magnetic field associated with a current (ESBPS)

If you hold a compass near a wire through which current is flowing, the needle on the compass will be deflected.

Since compasses work by pointing along magnetic field lines, this means that there must be a magnetic field near the wire through which the current is flowing.

The magnetic field produced by an electric current is always oriented perpendicular to the direction of the current flow. Below is a sketch of what the magnetic field around a wire looks like when the wire has a current flowing in it. We use B⃗ to denote a magnetic field and arrows on field lines to show the direction of the magnetic field. Note that if there is no current there will be no magnetic field.

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The direction of the current in the conductor (wire) is shown by the central arrow. The circles are field lines and they also have a direction indicated by the arrows on the lines. Similar to the situation with electric field lines, the greater the number of lines (or the closer they are together) in an area the stronger the magnetic field.

Important: all of our discussion regarding field directions assumes that we are dealing with conventional current.

To help you visualise this situation, stand a pen or pencil straight up on a desk. The circles are centred around the pencil or pen and would be drawn parallel to the surface of the desk. The tip of the pen or pencil would point in the direction of the current flow.

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You can look at the pencil or pen from above and the pencil or pen will be a dot in the centre of the circles. The direction of the magnetic field lines is counter-clockwise for this situation.

To make it easier to see what is happening we are only going to draw one set of circular fields lines but note that this is just for the illustration.