A coil of self-inductance L is connected in series with a bulb B and an AC source. Brightness of the bulb decreases when
A
a capacitance of reactance XC = XL is included in the same citcuit.
B
an iron rod is inserted in the coil.
C
frequency of the AC source is decreased.
D
number of turns in the coil is reduced.
2
NEET 2013
MCQ (Single Correct Answer)
+4
-1
The condition under which a microwave oven heats up a food item containing water molecules most efficiently is
A
Microwaves are heat waves, so always produce heating.
B
Infra-red waves produce heating in a microwave oven.
C
The frequency of the microwaves must match the resonant frequency of the water molecules.
D
The frequency of the microwaves has no relation with natural frequency of water molecules.
3
NEET 2013
MCQ (Single Correct Answer)
+4
-1
A plano convex lens fits exactly into a plano concave lens. Their plane surfaces are parallel to each other. If lenses are made of different materials of refractive indices $$\mu $$1 and $$\mu $$2 and R is the radius of curvature of the curved surface of the lenses, then the focal length of the combination is