- AAmplification.
- BRectification.
- CStabilisation.
- DAll of the above.
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The magnetic field at the centre of a circular coil of radius r is π times that due to a long straight wire at a distance r from it, for equal currents. Figure here shows three cases : in all cases the circular part has radius r and straight ones are infinitely long. For same current the B field at the centre P in cases 1, 2, 3 have the ratio
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(a) |
(b) |
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(c) - |
(d) |
Six charges, three positive and three negative of equal magnitude are to be placed at the vertices of a regular hexagon such that the electric field at O is double the electric field when only one positive charge of same magnitude is placed at R. Which of the following arrangements of charges is possible for P, Q, R, S, T and U respectively

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(a) +, -, +, -, -, + |
(b) +, -, +, -, +, - |
(c) +, +, -, +, -, - |
(d) -, +, +, -, +, - |
The adjoining figure shows two bulbs B1 and B2 resistor R and an inductor L. When the switch S is turned off

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(a) Both B1 and B2 die out promptly |
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(b) Both B1 and B2 die out with some delay |
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(c) B1 dies out promptly but B2 with some delay |
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(d) B2 dies out promptly but B1 with some delay |
0.2 Fcapacitor is charged to 600 V by a battery. On removing the battery, it is connected with another parallel plate condenser of 1F. The potential decreases to
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(a) 100 volts |
(b) 120 volts |
(c) 300 volts |
(d) 600 volts |
A region surrounding a stationary electric dipoles has
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(a) Magnetic field only |
(b) Electric field only |
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(c) Both electric and magnetic fields |
(d) No electric and magnetic fields |
Two coherent light sources S1 and S2 (l= 6000 Å) are 1mm apart from each other. The screen is placed at a distance of 25 cm from the sources. The width of the fringes on the screen should be
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(a) 0.015 cm |
(b) 0.025 cm |
(c) 0.010 cm |
(d) 0.030 cm |
X-rays and gamma rays are both electromagnetic waves. Which of the following statements is true
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(a) In general X-rays have larger wavelength than of gamma rays |
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(b) X-rays have smaller wavelength than that of gamma rays |
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(c) Gamma rays have smaller frequency than that of X-rays |
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(d) Wavelength and frequency of X-rays are both larger than that of gamma rays |
The ratio of minimum to maximum wavelength in Balmer series is
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(a) 5 : 9 |
(b) 5 : 36 |
(c) 1 : 4 |
(d) 3 : 4 |
In the following Wheatstone bridge P/Q = R/S. If key K is closed, then the galvanometer will show deflection
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(a) In left side |
(b) In right side |
(c) No deflection |
(d) In either side |