Two cells, e.m.f. of each is E and internal resistance r are connected in parallel between the resistance R. The maximum energy given to the resistor will be, only when
|
(a) R = r/2 |
(b) R = r |
(c) R = 2r |
(d) R = 0 |
(a) R = r/2
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A bar magnet of magnetic moment 200 A-m2 is suspended in a magnetic field of intensity 0.25 N/A-m. The couple required to deflect it through 30o is
|
(a) 50 N-m |
(b) 25 N-m |
(c) 20 N-m |
(d) 15 N-m |
A circular coil of radius 4 cm has 50 turns. In this coil a current of 2 A is flowing. It is placed in a magnetic field of 0.1 
. The amount of work done in rotating it through 180° from its equilibrium position will be
|
(a) 0.1 J |
(b) 0.2 J |
(c) 0.4 J |
(d) 0.8 J |
When a resistance of 2 ohm is connected across the terminals of a cell, the current is 0.5 A. When the resistance is increased to 5 ohm, the current is 0.25 A. The e.m.f. of the cell is
|
(a) 1.0 V |
(b) 1.5 V |
(c) 2.0 V |
(d) 2.5 V |
A magnet oscillating in a horizontal plane has a time period of 2 second at a place where the angle of dip is 30o and 3 seconds at another place where the angle of dip is 60o. The ratio of resultant magnetic fields at the two places is
|
(a) |
(b) |
(c) |
(d) |
Solid targets of different elements are bombarded by highly energetic electron beams. The frequency (f) of the characteristic X-rays emitted from different targets varies with atomic number Z as
|
(a) f ∝ |
(b) f ∝ |
(c) f ∝ Z |
(d) f ∝ |
