Ray Optics and Optical Instruments — Physics STD 12 Science — Question

As the switch S is closed in the circuit shown in figure, current passed through it is

(a) 4.5 A

(b) 6.0 A

(c) 3.0 A

(d) Zero

Which of the following statement is not correct

(a) Photographic plates are sensitive to infrared rays

(b) Photographic plates are sensitive to ultraviolet rays

(c) Infra-red rays are invisible but can cast shadows like visible light

(d) Infrared photons have more energy than photons of visible light

If a current of 3.0 amperes flowing in the primary coil is reduced to zero in 0.001 second, then the induced e.m.f. in the secondary coil is 15000 volts. The mutual inductance between the two coils is

(a) 0.5 henry

(b) 5 henry

(c) 1.5 henry

(d) 10 henry

The magnetic field in a coil of 100 turns and 40 square cm area is increased from 1 Tesla to 6 Tesla in 2 second. The magnetic field is perpendicular to the coil. The e.m.f. generated in it is

(a)

(b) 1.2 V

(c) 1.0 V

(d)

A bright star is indicated to have a brightness magnitude of – 5 compared to a star of brightness zero magnitude. It means that this star compared to the reference star of zero brightness is           

(a) 100 times less bright	(b) 5 times more bright
(c) 5 times less bright	(d) 100 times more bright

If a star is moving towards the earth, then the lines are shifted towards

(a) Red

(b) Infrared

(c) Blue

(d) Green

Consider the circuits shown in the figure. Both the circuits are taking same current from battery but current through R in the second circuit is  th of current through R in the first circuit. If R is 11 W, the value of R₁

(a) 9.9 W

(b) 11 W

(c) 8.8 W

(d) 7.7 W

Which of the following is the most suitable material for making permanent magnet?