Page 10 - 10-phy-15 Electromagnetism

15. Electromagnetism eLearn.Punjab

Now apply Fleming’s left hand rule to each side of the coil (Fig 15.8).

We can see that on PQ side of the loop force acts upward while on the RS side of the loop force acts

downward. It is because the direction of the current through the two sides of the loop facing the

two poles is at right angles to the field

but opposite to each other. Activity

The two forces which are equal in Suppose direction of current passing through two straight wires is
magnitude but opposite in direction same. Draw the pattern of magnetic field of current due to each wire.
form a couple The resulting torque Would the wires attract or repel each other?

due to this couple

rotates the loop and

the magnitude of the

torque acting on the

loop is proportional

to the magnitude of

the current passing

through the loop.

If we increase the

number of loops, the

turning effect is also

increased. This is the

working principle of

electric motors.

Animation 15.6 : Rotating coil
Source & Credit : waiferx

15.4 D.C. MOTOR

We can see from Fig. 15.9 that the simple coil placed in a magnet cannot rotate more than 90°. The

forces push the PQ side of the coil up and the RS side of the loop down until the loop reaches the

vertical position.

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