A horizontal bar is rotating at an angular velocity v about a vertical axis through its centre in a region of constant magnetic field B directed parallel to its vertical axis.
What is the e.m.f. between the two ends of the bar?
- It is zero.
- It is proportional to the product Bv.
- It is proportional to the product Bv2.
- It is proportional to the product B2v2.
A coil carries a current in an anti-clockwise direction while a wire located at the axis of the coil carries a current that is coming out of the paper, as shown below.
- It does not experience any force.
- The resultant force on the coil is zero.
- It experiences an attractive force towards the centre.
- It experiences a repulsive force away from the centre.
Both currents are parallel to the magnetic fields produced by their counterparts; hence the currents will not interact with the magnetic field and produce a force.
A 20-turn square coil of side 8.0 mm is pivoted at the centre and placed in a magnetic field of flux density 0.010 T such that two sides of the coil are parallel to the field and two sides are perpendicular to the field, as shown below. A current of 5.0 mA is passed through the coil.
- 1.6 x 10-9 N m
- 3.2 x 10-8 N m
- 6.4 x 10-8 N m
- 3.2 x 10-5 N m
Magnetic force on a single coil = BIL
= 0.01 x 5.0 x 10-3 x 8.0 x 10-3
= 4.0 x 10-7 N m
Torque acting on the coil = 20 x 4.0 x 10-7 x 8.0 x 10-3
= 6.4 x 108 N m.
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