Atomic and Nuclear Physics — Physics STD 12 Science — Question

A battery of e.m.f. 10 V and internal resistance 0.5 ohm is connected across a variable resistance R. The value of R for which the power delivered in it is maximum is given by(a) 2.0 ohm(b) 0.25 ohm(c) 1.0 ohm(d) 0.5 ohm

In an AC generator, a coil with N turns, all of the same area A and total resistance R, rotates with frequency 1rad/ s in a magnetic field B. The maximum value of emf generated in the coil is:

The sensitivity of a tangent galvanometer is increased if(a) Number of turn decreases (b) Number of turn increases(c) Field increases(d) None of the above

A concave mirror is used to focus the image of a flower on a nearby well 120 cm from the flower. If a lateral magnification of 16  is desired, the distance of the flower from the mirror should be(a) 8 cm  (b) 12 cm (c) 80 cm(d) 120 cm

Assertion   :   Two bulbs of same wattage, one having a carbon filament and the other having a metallic filament are connected in series. Metallic bulbs will glow more brightly than carbon filament bulb. 
Reason      : Carbon is a semiconductor.(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.

The number of electrons made available for conduction by dopant atoms depends strongly upon

The spectrum of iodine gas under white light will be(a) Only violet(b) Bright lines(c) Only red lines(d) Some black bands in continuous spectrum

An electric dipole is placed in an electric field generated by a point charge(a) The net electric force on the dipole must be zero(b) The net electric force on the dipole may be zero(c) The torque on the dipole due to the field must be zero(d) The torque on the dipole due to the field may be zero