#2621

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.

#2622

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.

#2623

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.

#2624

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.

#2625

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.

#2626

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).

#2627

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

(a) diagonal

(b) diameter

(c) radius

(d) hypotenuse

Explanation: SHM corresponds to projection of uniform circular motion onto a radius, giving sinusoidal motion.

#2628

How many 60 watt lamps may be safely run on a 230 volt circuit fitted with a 5-amp fuse?

(a) 4

(b) 20

(c) 19

(d) 2

Explanation: Each 60 W lamp draws 60/230 ≈ 0.261 A; 5 A ÷ 0.261 A ≈ 19 lamps, so option B is correct.

#2629

Thermistors may be in the form of:

(a) Either of these

(b) Washers

(c) Beads

(d) Rods

Explanation: Thermistors are manufactured in various shapes including beads, rods, and washers, so 'Either of these' covers the forms listed.

#2630

A hole in p-type may be due to:

(a) Either (a) or (b)

(b) Breaking of some covalent bond

(c) Trivalent impurity

(d) Germanium

Explanation: Holes in p-type material arise from trivalent impurity atoms creating acceptor levels or from breaking of covalent bonds; thus either (a) or (b) is correct.

#2631

Charge of +1 esu, +2 esu and +3 esu are placed at the three corners of a square. What charge should be placed at the fourth corner so that potential at the centre may be zero? One side of the square is 1/2 cm.

(a) -4 esu

(b) +4 esu

(c) +6 esu

(d) -6 esu

Explanation: Potential at centre is proportional to sum of corner charges (equal distances), so fourth charge must be -(1+2+3) = -6 esu to make sum zero.

#2632

Objects may acquire an excess or deficiency of charge by

(a) shielding them

(b) grounding them

(c) rubbing them together

(d) applying Coulomb's principle

Explanation: Common methods include friction (rubbing) which transfers charge; grounding is also a method but rubbing is the classic example listed.

#2633

44 As electric field intensity is a potential gradient, it may be expressed in the units of N C⁻¹ or

(a) volt metre

(b) joule

(c) volt

(d) volt per metre

Explanation: Electric field can be expressed as N/C or V/m which is volt per metre.

#2634

An inductor may store energy in its

(a) coils

(b) electric field

(c) magnetic field

(d) electric and magnetic fields

Explanation: An inductor stores energy in the magnetic field created around its coil when current flows, so option C is correct.

#2635

An inductor may store energy in

(a) its electric field

(b) a neighbouring circuit

(c) its magnetic field

(d) its coils

Explanation: An inductor stores energy in its magnetic field when current flows through it.

#2636

456 A generator running in reverse may be called as

(a) d.c. generator

(b) motor

(c) commutator

(d) a.c. generator

Explanation: A generator operated in reverse functions as a motor, so option C is correct.

#2637

"All magnetic effects may be due to circulating currents (i.e., moving charges)." This idea belongs initially to:

(a) Ampere

(b) Maxwell

(c) Tesla

(d) Faraday

Explanation: Ampère originally proposed that magnetic effects arise from electric currents (circulating charges), attributing magnetism to currents.

#2638

A semiconductor device is connected in a series circuit with a battery and a resistance. A current is found to pass through the circuit. If the polarity of the battery is reversed, the current drops almost to zero. The device may be

(a) An intrinsic semiconductor

(b) An N-type semiconductor

(c) A P-N junction

(d) A P-type semiconductor

Explanation: A P-N junction (diode) conducts easily in one polarity (forward bias) and blocks current when the polarity is reversed (reverse bias), so the behaviour matches a P-N junction.

#2639

An inductor may store energy in:

(a) Its magnetic field

(b) Its electric field

(c) Its coil

(d) A neighbouring circuit

Explanation: An inductor stores energy in the magnetic field created by current through its coil.

#2640

Stress may cause a change in:

(a) Any of these

(b) Volume

(c) Shape

(d) Length

Explanation: Stress can lead to changes in length, volume, or shape depending on its nature, so any of these may change.

May 2025 Current Affairs MCQs & Solutions