Solution:
Key concept: As we know whenever the number of magnetic lines of force (magnetic flux) passing through a circuit changes, an e.m.f is produced in the circuit called induced e.m.f. The induced e.m.f persists only as long as there is a change or cutting of flux.
In this problem, magnetic flux linked with the isolated coil changes when the coil is placed in the region of a time varying magnetic field, the coil moving in a constant magnetic field or in time varying magnetic field.
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Four wires AB, BC, CD, DA of resistance 4 ohm each and a fifth wire BD of resistance 8 ohm are joined to form a rectangle ABCD of which BD is a diagonal. The effective resistance between the points A and B is
|
(a) 24 ohm |
(b) 16 ohm |
(c) |
(d) |
A and B are two concentric circular conductors of centre O and carrying currents 
and 
as shown in the adjacent figure. If ratio of their radii is 1 : 2 and ratio of the flux densities at O due to A and B is 1 : 3, then the value of 
is
|
(a) |
(b) |
(c) |
(d) |
The focal length of the field lens (which is an achromatic combination of two lenses) of telescope is 90 cm. The dispersive powers of the two lenses in the combination are 0.024 and 0.036. The focal lengths of two lenses are
|
(a) 30 cm and 60 cm |
(b) 30 cm and – 45 cm |
|
(c) 45 cm and 90 cm |
(d) 15 cm and 45 cm |
A radioactive nucleus with Z protons and N neutrons emits an a-particle, 2b-particles and 2 gamma rays. The number of protons and neutrons in the nucleus left after the decay respectively, are
|
(a) Z – 3, N – 1 |
(b) Z – 2, N – 2 |
(c) Z – 1, N – 3 |
(d) Z, N – 4 |
When a body is earth connected, electrons from the earth flow into the body. This means the body is….
|
(a) Unchanged |
(b) Charged positively |
(c) Charged negatively |
(d) An insulator |
