NEET-XII-Physics
36: Permanent Magnets
- #17A moving-coil galvanometer has a 50-turn coil of size 2 cm × 2 cm. It is suspended between the magnetic poles producing a magnetic field of 0.5 T. Find the torque on the coil due to the magnetic field when a current of 20 mA passes through it.Ans : Given:
Number of turns in the coil, n = 50
Area of the cross section of the coil, A = 2 cm × 2 cm = 2 × 2 × 10-4 m2
Current flowing through the coil, I = 20 × 10-3 A
Magnetic field strength due to the presence of the poles, B = 0.5 T
The torque experienced by the coil placed in an external magnetic field `` \left(\tau \right)`` is given by
`` \tau \mathit{=}nI\left(\stackrel{\mathit{\to }}{A}\mathit{\times }\stackrel{\mathit{\to }}{B}\right)``
`` \Rightarrow \tau \mathit{=}nIAB\,\mathrm{\,sin\,}90°``
`` \Rightarrow \tau =50\times 20\times {10}^{-3}\times 4\times {10}^{-4}\times 0.5``
`` \Rightarrow \tau =2\times {10}^{-4}\,\mathrm{\,N\,}-\,\mathrm{\,m\,}``
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