Electric Charges and Fields — Physics STD 12 Science — Question

A semiconductor X is made by doping a germanium crystal with arsenic (Z = 33). A second semiconductor Y is made by doping germanium with indium (Z = 49). The two are joined end to end and connected to a battery as shown. Which of the following statements is correct

(a) X is P-type, Y is N-type and the junction is forward biased

(b) X is N-type, Y is P-type and the junction is forward biased

(c) X is P-type, Y is N-type and the junction is reverse biased

(d) X is N-type, Y is P-type and the junction is reverse biased

Which of the following is NOT a postulate of Bohr's model of the hydrogen atom? 

Wavelength of a 1 keV photon is . What is the frequency of 1 MeV photon

(a) 1.24

(b) 2.4

(c) 1.24

(d) 2.4

A virtual image three times the size of the object is obtained with a concave mirror of radius of curvature 36 cm. The distance of the object from the mirror is

(a) 5 cm

(b) 12 cm

(c) 10 cm

(d) 20 cm

Correct exposure for a photographic print is 10 seconds at a distance of one metre from a point source of 20 candela. For an equal fogging of the print placed at a distance of 2 m from a 16 candela source, the necessary time for exposure is

(a) 100 sec

(b) 25 sec

(c) 50 sec

(d) 75 sec

The heat generated through 2 ohm and 8 ohm resistances separately, when a condenser of 200 μF capacity charged to 200 V is discharged one by one, will be

(a) 4 J and 16 J respectively	(b) 16 J and 4 J respectively
(c) 4 J and 8 J respectively	(d) 4 J and 4 J respectively

A spectral line λ = 5000 Å in the light coming from a distant star is observed as a 5200 Å. What will be recession velocity of the star

(a) 1.15

(b) 1.15

(c) 1.15

(d) 1.15 km/sec

The air film in a Newton's ring apparatus is replaced by an oil film. The radii of the rings:

0.2 Fcapacitor is charged to 600 V by a battery. On removing the battery, it is connected with another parallel plate condenser of 1F. The potential decreases to

(a) 100 volts

(b) 120 volts

(c) 300 volts

(d) 600 volts

Nucleus produced due to a-decay of the nucleus   is

(a)

(b)

(c)

(d)