A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. The energy required to rotate it by 60º is W. Now the torque required to keep the magnet in this new position is
Wext = Uf – Vi
= – MB cos 60° – (–MB)
= MB(1 – cos 60°) = MB/2 = W
r = MB sin 60° = MB $\dfrac{\sqrt{3}}{2}$ =$ \sqrt{3}$W
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Which of the following combinations should be selected for better tuning of an L–C–R circuit used for communication? |
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A linear aperture whose width is 0.02 cm is placed immediately in front of a lens of focal length 60 cm. The aperture is illuminated normally by a parallel beam of wavelength 5 × 10–5 cm. The distance of the first dark band of the diffraction pattern from the centre of the screen is |
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