#2201

Surface tension of a liquid may be defined as

(a) Surface energy per unit area

(b) Heat energy per unit area

(c) P.E. per unit area

(d) K.E. per unit area

Explanation: Surface tension is the surface energy per unit area (or work required to increase surface area), so option C is correct.

#2202

67. A body in equilibrium may not have:

(a) Momentum

(b) Velocity

(c) Acceleration

(d) Kinetic energy

Explanation: A body in equilibrium has zero acceleration; it may have velocity (dynamic equilibrium), so it 'may not have' acceleration.

#2203

Temperature of Argon kept in a vessel is raised by 1°C at constant volume. Heat supplied to the gas may be taken partly as translational and partly rotational kinetic energies. Their respective shares are

(a) 60%, 40%

(b) 40%, 60%

(c) 100%, zero

(d) 50%, 50%

Explanation: Argon is a monatomic gas, so all supplied heat at constant volume goes to translational degrees of freedom (100%) and none to rotational (0%).

#2204

Absolute zero may be regarded as the temperature at which

(a) all substances are solids

(b) all gases become liquids

(c) water freezes

(d) molecular motion in a gas would cease

Explanation: Absolute zero is defined as the temperature at which molecular motion would cease.

#2205

1. Surface tension may be defined as

(a) free surface energy per unit volume.

(b) the work done per unit area in increasing the surface area of a liquid under isothermal conditions.

(c) the work done per unit area in increasing the surface area of a liquid under adiabatic conditions.

(d) the work done per unit area in increasing the surface area of a liquid both under isothermal and adiabatic conditions.

Explanation: Surface tension is defined as work done per unit area to increase surface area under isothermal conditions (option A).

#2206

If a bar is made of copper whose coefficient of linear expansion is one and a half times that of iron, the ratio of the force developed in the copper bar to the iron bar of identical lengths and cross-sections, when heated through the same temperature range (Young's modulus for copper may be taken to be equal to that of iron) is

(a) 3/2

(b) 4/9

(c) 9/4

(d) 2/3

Explanation: Force developed ∝ YαΔT; with equal Y and ΔT, ratio = α_copper / α_iron = 1.5/1 = 3/2.

#2207

A light rod of length 2 m is suspended from the ceiling horizontally by means of two vertical wires of equal length tied to its ends. One wire is steel with cross-sectional area 1×10^-9 m^2 and the other is brass with cross-sectional area 2×10^-9 m^2. The position along the rod from the steel wire at which a weight may be hung to produce equal stress in both wires is

(a) 1.5 m

(b) 0.67 m

(c) 1.0 m

(d) 1.33 m

Explanation: Equal stress means tensions are proportional to areas (T_s/T_b = A_s/A_b = 1/2). Balancing torques: (1/2)T_b·x = T_b·(2−x) gives x = 4/3 ≈ 1.33 m from the steel end.

#2208

A child whose class is in a windowless room may have to be assigned to another class if he/she suffers from ____.

(a) Acrophobia

(b) Agoraphobia

(c) Claustrophobia

(d) None of these

Explanation: Claustrophobia is the fear of confined or enclosed spaces, so a windowless room could trigger this condition.

#2209

A paraprofessional may properly engage in all of the following activities except

(a) Assisting on parents night

(b) Conferring with parents about a child behaviour

(c) Making short answer tests

(d) None of these

Explanation: Paraprofessionals generally should not confer with parents about student behavior without a certified teacher present; such communications are typically handled by certified staff.

#2210

The light reflected by a plane mirror may form a real image

(a) If the rays incident on the mirror are diverging

(b) under no circumstances

(c) If the rays incident on the mirror are converging

(d) If the object is placed very close to the mirror

Explanation: A plane mirror can form a real image only if the incident rays on the mirror are already converging so that reflection brings them to a focus.

#2211

A LASER beam may be used to measure very large distance because it is

(a) unidirectional

(b) coherent

(c) monochromatic

(d) not absorbed

Explanation: Lasers are highly coherent, which allows precise interference and distance measurements over long ranges.

#2212

At what distance from a concave mirror of focal length 10 cm must an object be placed in order that an image double its size may be obtained?

(a) either 5 cm or 15 cm

(b) 5 cm only

(c) at 10 cm

(d) 15 cm only

Explanation: A concave mirror gives a magnification of 2 for an object at 15 cm (real inverted) and a virtual erect magnification 2 for an object at 5 cm, so both positions apply.

#2213

A diverging lens may not have

(a) positive focal length

(b) one plane surface

(c) one convex surface

(d) negative focal length

Explanation: A diverging lens always has a negative focal length, so it cannot have a positive focal length.

#2214

Light travelling from a transparent medium to air undergoes total internal reflection at an angle of incidence of 45°. Then refractive index of the medium may be

(a) 1.5

(b) √2

(c) 1.3

(d) 1.1

Explanation: For total internal reflection at 45°, the critical angle must be ≤45°, so n ≥ 1/sin45° = √2 ≈1.414; 1.5 satisfies this.

#2215

127. Optical fibres may be used

(a) to transmit signals without appreciable loss of energy

(b) to arrange rains

(c) to store solar energy

(d) to transmit signal with appreciable loss of energy

Explanation: Optical fibres are designed to transmit signals with very low loss, making option B correct.

#2216

The two vectors to be combined have magnitudes 65 N and 30 N. Which of the following magnitudes, the resultant may have?

(a) 100 N

(b) 15 N

(c) 85 N

(d) 125 N

Explanation: Resultant magnitude lies between |65-30| = 35 N and 65+30 = 95 N, so 85 N is possible while the others are outside this range.

#2217

A force of 120 N and a force of 20 N acting simultaneously at a point may produce a resultant force of

(a) 50 N

(b) 140 N

(c) 150 N

(d) none of these

Explanation: Maximum resultant is 120+20 = 140 N and minimum is 100 N, so 140 N is a possible resultant while 50 N and 150 N are not.

#2218

Which of the sets given below may represent the magnitudes of three vectors whose resultant is zero?

(a) 4, 5, 7

(b) 0.5, 1, 2

(c) 17, 5, 8

(d) 3, 9, 5

Explanation: Three vectors can sum to zero if their magnitudes satisfy triangle inequalities; 4, 5, 7 satisfy these (4+5>7, etc.), so they can form a closed triangle.

#2219

Simple harmonic motion may be assumed as a projection of uniform circular motion along a

(a) hypotenuse

(b) diagonal

(c) radius

(d) diameter

Explanation: The standard demonstration derives SHM as the projection of uniform circular motion onto a diameter (a line through the circle).

#2220

Simple harmonic motion may be assumed as projection of uniform circular motion along a

(a) diagonal

(b) diameter