81.

If an alternating voltage is represented as E = 141 sin (628 t), then the rms value of the voltage and the frequency are respectively

• 141 V, 628 Hz

• 100 V, 50 Hz

• 100 V, 100 Hz

• 141 V, 100 Hz

A step-down transformer is used on a 1000 V line to deliver 20 A at 120 V at the secondary coil. If the efficiency of the transformer is 80%, the current drawn from the line is

• 3 A

• 30 A

• 0.3 A

• 2.4 A

Band spectrum is also called

• molecular spectrum

• atomic spectrum

• flash spectrum

• line absorption spectrum

A fish at a depth of 12 cm in water is viewed by an observer on the bank of a lake. To what height the image of the fish is raised ?

• 9 cm

• 12 cm

• 3.8 cm

• 3 cm

A ray of light is incident at 50° on the middle of one of the two mirrors arranged at an angle of 60° between them. The ray then touches the second mirror, gets reflected back to the first mirror, making an angle of incidence

• 50°

• 60°

• 70°

• 80°

In a compound microscope, the intermediate image is

• virtual, erect and magnified

• real, erect and magnified

• real, inverted and magnified

• virtual, erect and reduced

A ray of light passes through an equilateral prism such that an angle of incidence is equal to the angle of emergence and the latter is equal to $\frac{3}{4}$th the angle of prism. The angle of deviation is

• 45°

• 39°

• 20°

• 30°

C¹⁴ has half-life 5700 yr. At the end of 11400 yr, the actual amount left is

• 0.5 of original amount

• 0.25 of original amount

• 0.125 of original amount

• 0.0625 of original amount

The ionization potential of hydrogen is 13.6 V. The energy required to remove an electron from the second orbit of hydrogen is

• 3.4 eV

• 6.8 eV

• 13.6 eV

• 1.51 eV

The depletion layer of a p-n junction

• is of constant width irrespective of the bias

• acts like an insulating zone under reverse bias

• has a width that increases with an increase in forward bias

• is depleted of ions