Electric Charges and Fields — Physics STD 12 Science — Question

Which of the following did Bohr use to explain his theory?

A rocket is going away from the earth at a speed of 10⁶ m/s If the wavelength of the light wave emitted by it be 5700 Å, what will be its Doppler's shift

(a) 200 Å

(b) 19 Å

(c) 20 Å

(d) 0.2 Å

When the electrical conductivity  of a semi-  conductor  is due to the breaking of its covalent bonds, then the semiconductor is said to be

(a) Donar

(b) Acceptor

(c) Intrinsic

(d) Extrinsic

To an observer on the earth the stars appear to twinkle. This can be ascribed to

(a) The fact that stars do not emit light continuously

(b) Frequent absorption of star light by their own atmosphere

(c) Frequent absorption of star light by the earth's atmosphere

(d) The refractive index fluctuations in the earth's atmosphere

A thin lens made of glass of refractive index 1.5 has a front surface + 11 D power and back surface – 6 D. If this lens is submerged in a liquid of refractive index 1.6, the resulting power of the lens is

(a) – 0.5 D

(b) + 0.5 D

(c) – 0.625 D

(d) + 0.625 D

Three charges Q(+q)  and (+q)  are placed at the vertices of an equilateral triangle of side l as shown in the figure. If the net electrostatic energy of the system is zero, then Q is equal to

(a)

(b) (-q)

(c) (+q)

(d) Zero

Figure shows two capacitors connected in series and joined to a battery. The graph shows the variation in potential as one moves from left to right on the branch containing the capacitors:

1. C₁ > C₂
2. C₁ = C₂
3. C₁ < C₂
4. The information is not sufficient to decide the relation between C₁ and C₂.

A straight conductor of length 0.4 m is moved with a speed of 7 m/s perpendicular to the magnetic field of intensity of 0.9 Wb/m². The induced e.m.f. across the conductor will be

(a) 7.25 V

(b) 3.75 V

(c) 1.25 V

(d) 2.52 V

Consider the following statements A to B  and identify the correct answer

A. Polarised light can be used to study the helical surface of nucleic acids.

B. Optics axis is a direction and not any particular line in the crystal

(a) A and B are correct	(b) A and B are wrong
(c) A is correct but B is wrong	(d) A is wrong but B is correct

In the given current distribution what is the value of I

(a) 3A

(b) 8 A

(c) 2A

(d) 5A