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Moving Charges And Magnetism
Question
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A short bar magnet of magnetic moment 0.4 JT-1 is placed in a uniform magnetic field of 0.16T. The magnet is stable equilibrium when the potential energy is

  • -0.64 J

  • zero

  • -0.082 J

  • 0.064 J

Answer

D.

0.064 J

We know that
U = - MB cos θ
For stable equilibrium θ = 0o
So, U = - MB

=- (0.4)(.16) = - 0.064 J 

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Some More Questions From Moving Charges And Magnetism Chapter

Two moving coil meters, M1 and M2 have the following particulars:
R1 = 10 Ω   N1 = 30,
A1 = 3.6 x 10–3 m2,  B1 = 0.25 T
R2 = 14 Ω;  N2 = 42,
A2 = 1.8 x 10–3 m2, B2 = 0.50 T
(The spring constants k are identical for the two meters).
Determine the ratio of (a) current sensitivity and (b) voltage sensitivity of M2 and M1.

Answer the following questions:
A charged particle enters an environment of a strong and non-uniform magnetic field varying from point to point both in magnitude and direction, and comes out of it following a complicated trajectory. Would its final speed equal the initial speed if it suffered no collisions with the environment?