Current Electricity — Physics STD 12 Science — Question

Two resistances R and 2R are connected in parallel in an electric circuit. The thermal energy developed in R and 2R are in the ratio:

1. 1 : 2
2. 2 : 1
3. 1 : 4
4. 4 : 1

An observer on earth observes that wave length of spectral line in spectrum of a milky way shifts towards red end of spectrum. According to the observer, the milky-way is:

A P-type semiconductor can be obtained by adding

(a) Arsenic to pure silicon	(b) Gallium to pure silicon
(c) Antimony to pure germanium	(d) Phosphorous to pure germanium

In a triode amplifier, the value of maximum gain is equal to

(a) Half the amplification factor	(b) Amplification factor
(c) Twice the amplification factor	(d) Infinity

A diffraction is obtained by using a beam of red light. What will happen if the red light is replaced by the blue light

(a) Bands will narrower and crowd full together

(b) Bands become broader and further apart

(c) No change will take place

(d) Bands disappear

A metal surface of work function 1.07 eV is irradiated with light of wavelength 332 nm. The retarding potential required to stop the escape of photo-electrons is

(a) 4.81 eV

(b) 3.74 eV

(c) 2.66 eV

(d) 1.07 eV

On what basis is the classification of electromagnetic waves done?

A transformer is employed to reduce 220 V to 11 V. The primary draws a current of 5 A and the secondary 90 A. The efficiency of the transformer is

(a) 20%

(b)  40%

(c) 70%

(d)  90%

Mutual inductance of two coils is M. If current change in time t in first coil is I, then induced emf in the second coil is: