83.
The electromagnet has 50 turns and a current of 1A flows through the coil. If the length of the magnet circuit is 200 mm, what is the magnetic field strength?

84.
If a copper disc is rotated rapidly below a freely suspended magnetic needle, the magnetic needle shall start rotating with a velocity

86.
A 200 turn coil having an axial length of 30 mm and a radius of 10 mm is pivoted in a magnetic field having a flux density of 0.8 T. If the coil carries a current of 0.5 A, the torque acting on the coil will be
[Hint. Torque = 2BIlNr N-m]

87.
The working of a meter is based on the use of a permanent magnet. In order to protect the meter functioning from stray magnetic fields

88.
The initial permeability of an iron rod is