The potential difference that must be applied to stop the fastest photoelectrons emitted by a nickel surface, having work function 5.01 eV, when ultraviolet light of 200 nm falls on it, must be

2.4 V
– 1.2 V
– 2.4 V
1.2 V

Solution

Atomic weight of boron is 10.81 and it has two isotopes ₅B¹⁰ and ₅B¹¹. Then ratio of ₅B₁₀: ⁵B¹¹ in nature would be

19 : 81
10 : 11
15 : 16
81 : 19

Solution

A transformer is used to light a 140 W, 24 V bulb from a 240 V a.c. mains. The current in the main cable is 0.7 A. The efficiency of the transformer is

63.8 %
83.3 %
16.7 %
36.2 %

Solution

Power of source = EI = 240 × 0.7 = 166

⇒ Efficiency =\(\frac{140}{160}\Rightarrow \eta =83.3\)%

When sound waves travel from air to water which one of the following remains constant?

Time period
Frequency
Velocity
Wavelength

Solution

Frequency remains constant if medium is changed.

Two planets of radii r₁ and r₂ are made from the same material. The ratio of the acceleration due to gravity g₁/g₂ at the surfaces of the two planets is

r₁/r₂
r₂/r₁
(r₁/r₂)²
(r₂/r₁)²

Solution

The resultant of two forces 3P and 2P is R. If the first force is doubled then the resultant is also doubled. The angle between the two forces is

60º
120º
70º
180º

Solution

Solve two equations : R² = 9P²+ 4P²+ 12P² cosθ and 4R²= 36P²+ 4P²+ 24P²cosθ.

In terms of Bohr radius r₀, the radius of the second Bohr orbit of a hydrogen atom is given by

4 r₀
8 r₀
√2 r₀
2 r₀

Solution

As r α n², therefore, radius of 2nd Bohr’s orbit = 4 r₀

The time constant of C–R circuit is

1/CR
C/R
C R
R/C

One milligram of matter convert into energy will give

90 joule
9 × 10³ joule
9 × 10⁵ joule
9 × 10¹⁰ joule

Solution

A crystal has a coefficient of expansion 13×10^-7 in one direction and 231 × 10^-7 in every direction at right angles to it. Then the cubical coefficient of expansion is

462 × 10^-7
244 × 10^-7
475 × 10^-7
257 × 10^-7

Solution

γ = α₁ + α₂ + α₃

=13 × 10^-7 + 231 × 10^-7 + 231 × 10^-7

= 475 × 10^-7

Hail storms are observed to strike the surface of the frozen lake at 30° with the vertical and rebound at 60° with the vertical. Assume contact to be smooth, the coefficient of restitution is

e = ¹⁄_√3
e = ¹⁄₃
e = √3
e = 3

Solution

If a source is transmitting electromagnetic wave of frequency 8.2 × 10⁶ Hz, then wavelength of the electromagnetic waves transmitted from the source will be

36.6 m
40.5 m
42.3 m
50.9 m

Solution

The ratio of maximum to minimum wavelength in Balmer series is

3 : 4
1 : 4
5 : 36
5 : 9

Solution

If coefficient of self induction of a coil is 1 H, an e.m.f. of 1V is induced, if

current flowing is 1A
current variation rate is 1 As^–1
current of 1A flows for one sec.
None of these

Solution

From e =LdI / dt, dI / dt = ^e⁄_L = ¹⁄₁ = 1 As^-1

A real image is formed by a convex lens. If we put a concave lens in contact with it, the combination again forms a real image. The new image

is closer to the lens system.
is farther form the lens system.
is at the original position.
may be any where depending on the focal length of the concave lens.

Solution

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