A variable condenser is permanently connected to a 100 V battery. If the capacity is changed from 2μF to 10 μF, then change in energy is equal to
|
(a) 2 |
(b) 2.5 |
(c) 3.5 |
(d) 4 |
(d) 4 
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The radioactive decay of uranium into thorium is expressed by the equation 
where ‘X’ is
|
(a) An electron |
(b) A proton |
(c) A deuteron |
(d) An alpha particle |
The half life period of a radioactive substance is 5 min. The amount of substance decayed in 20 min will be
|
(a) 93.75% |
(b) 75% |
(c) 25% |
(d) 6.25% |
An electric potential difference will be induced between the ends of the conductor shown in the diagram, when the conductor moves in the direction
|
(a) P |
(b) Q |
(c) L |
(d) M |
Two concentric coplanar circular loops of radii 
and 
carry currents of respectively 
and 
in opposite directions (one clockwise and the other anticlockwise.) The magnetic induction at the centre of the loops is half that due to alone at the centre. If 
. the value of 
is
|
(a) 2 |
(b) 1/2 |
(c) 1/4 |
(d) 1 |
Length of a hollow tube is 5m, it’s outer diameter is 10 cm and thickness of it’s wall is 5 mm. If resistivity of the material of the tube is 1.7 × 
W × m then resistance of tube will be
|
(a) 5.6 × 10–5 W |
(b) 2 × 10–5 W |
(c) 4 × 10–5 W |
(d) None of these |
Assertion : Leclanche cell is used, when constant supply of electric current is not required.
Reason : The e.m.f. of a Leclanche cell falls, if it is used continuously.
|
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
|
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
|
(c) If assertion is true but reason is false. |
|
(d) If the assertion and reason both are false. |