Electromagnetic Waves — Physics STD 12 Science — Question

Effective capacitance between A and B in the figure shown is (all capacitance are in mF)

(a) 21 mF

(b) 23 mF

(c) F

(d)

Temperature above which a ferromagnetic substance becomes paramagnetic is called

(a) Critical temperature	(b) Boyle's temperature
(c) Debye's temperature	(d)  Curie temperature

The capacity of a parallel plate capacitor increases with the

(a) Decrease of its area	(b) Increase of its distance
(c) Increase of its area	(d) None of the above

Two circular loops of equal radii are placed coaxially at some separation. The first is cut and a battery is inserted in between to drive a current in it. The current c~anges slightly because of the variation in resistance with temperature. During this period, the two loops:

1. Attract each other.
2. Repel each other.
3. Do not exert any force on each other.
4. Attract or repel each other depending on the sense of the current.

The patient is asked to drink  for examining the stomach by X-rays because X-rays are

(a) Reflected by heavy atoms	(b) Refracted by heavy atoms
(c) Less absorbed by heavy atoms	(d) More absorbed by heavy atoms

Voltmeters V₁ and V₂ are connected in series across a D.C. line.  V₁ reads 80 volts and has a per volt resistance of 200 ohms.  V₂ has a total resistance of 32 kilo ohms.  The line voltage is

(a) 120 volts

(b) 160 volts

(c) 220 volts

(d) 240 volts

Two heater wires of equal length are first connected in series and then in parallel. The ratio of heat produced in the two cases is

(a) 2 : 1

(b) 1 : 2

(c) 4 : 1

(d) 1 : 4

The current gain of a transistor in common base mode is 0.995. The current gain of the same transistor in common emitter mode is?

What happens to the plates of the apparatus if we measure alternating charge using a Gold-leaf oscilloscope?

By a monochromatic wave, we mean

(a) A single ray	(b) A single ray of a single colour
(c) Wave having a single wavelength	(d) Many rays of a single colour