Explanation:
Iron is a ferromagnetic substance, so there are no magnetic lines of force inside it. So to protect the sensitive equipment from external magnetic field, it should be placed inside an iron can.
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Plane figures made of thin wires of resistance R = 50 milli ohm/metre are located in a uniform magnetic field perpendicular into the plane of the figures and which decrease at the rate dB/dt = 0.1 m T/s. Then currents in the inner and outer boundary are. (The inner radius a = 10 cm and outer radius b = 20 cm)
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(a) 10– 4 A (Clockwise), 2 × 10– 4 A (Clockwise) |
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(b) 10– 4 A (Anticlockwise), 2 × 10– 4 A (Clockwise) |
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(c) 2 × 10– 4 A (clockwise), 10– 4 A (Anticlockwise) |
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(d) 2 × 10– 4 A (Anticlockwise), 10– 4 A (Anticlockwise) |
Penetrating power of X-rays can be increased by
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(a) Increasing the potential difference between anode and cathode |
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(b) Decreasing the potential difference between anode and cathode |
| (c) Increasing the cathode filament current |
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(d) Decreasing the cathode filament current |
Fraunhofer lines are obtained in
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(a) Solar spectrum |
(b) The spectrum obtained from neon lamp |
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(c) Spectrum from a discharge tube |
(d) None of the above |
An electric bulb is rated 60W, 220V. The resistance of its filament is
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(a) 708 W |
(b) 870 W |
(c) 807 W |
(d) 780 W |
Two concentric circular coils of ten turns each are situated in the same plane. Their radii are 20 and 40 cm and they carry respectively 0.2 and 0.3 ampere current in opposite direction. The magnetic field in 
at the centre is
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(a) |
(b) |
(c) |
(d) |
