Current Electricity — Physics STD 12 Science — Question

The shape of wave front at a very large distance from source is ______.

Carbon, silicon and germanium have four valence electrons each. At room temperature the appropriate statement is:

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

A slit of width a is illuminated by white light. For red light (λ = 6500 Å), the first minima is obtained at θ = 30°. Then the value of a will be

(a) 3250 Å

(b) 6.5

(c) 1.24 microns

(d) 2.6

Consider an electron (m = 9.1   confined by electrical forces to move between two rigid walls separated by 1.0  metre, which is about five atomic diameters. The quantised energy value for the lowest stationary state is

(a) 12

(b) 6.0

(c) 6.0

(d) 6 Joule

Let r be the distance of a point on the axis of a magnetic dipole from its centre. The magnetic field at such a point is proportional to:

Light of wavelength 1824 Å, incident on the surface of a metal, produces photo-electrons with maximum energy 5.3 eV. When light of wavelength 1216 Å is used, the maximum energy of photoelectrons is 8.7 eV. The work function of the metal surface is

(a) 3.5 eV

(b) 13.6 eV

(c) 6.8 eV

(d) 1.5 eV

If the wavelength of light is 4000 Å, then the number of waves in 1 mm length will be

(a) 25

(b) 0.25

(c) 0.25

(d) 25

In a triclinic crystal system

(a) a ≠ b ≠ c, α ≠ β ≠ γ	(b) a = b = c, α ≠ β  ≠ γ
(c) a ≠ b ≠ c, α ≠  β =  γ	(d) a  = b ≠ c, α  = β = γ