#2221

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.

#2222

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.

#2223

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.

#2224

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.

#2225

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.

#2226

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.

#2227

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.

#2228

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.

#2229

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.

#2230

"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.

#2231

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.

#2232

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.

#2233

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.

#2234

X-rays spectrum may be

(a) discontinuous spectrum

(b) continuous and line spectrum

(c) continuous spectrum

(d) line spectrum

Explanation: X-ray emissions include both a continuous Bremsstrahlung background and discrete characteristic line spectra, so both types occur.

#2235

(131) Nucleus of a hydrogen atom may contain:

(a) One proton and two neutrons

(b) One proton only

(c) Any of these

(d) One proton and one neutron

Explanation: Hydrogen nuclei can be a single proton (protium), proton+neutron (deuteron), or proton+two neutrons (triton), so any of these.

#2236

A nucleus with an excess of neutrons may decay radioactively with the emission of:

(a) A neutron

(b) An electron

(c) A positron

(d) A proton

Explanation: The OCR answer key lists option A for this question in the answer listing provided for question 100.

#2237

Which of the following describes that the time interval between two events may be different in different frames of reference?

(a) Mass variation

(b) Time dilation

(c) Simultaneously

(d) Length contraction

Explanation: Time dilation is the relativistic effect where elapsed time between events differs between reference frames.

#2238

(132) Nucleus of a hydrogen atom may contain:

(a) One proton only

(b) One neutron only

(c) Two protons and one neutron

(d) Two protons and two neutrons

Explanation: The simplest hydrogen nucleus contains one proton only; other options do not represent hydrogen nuclei.

#2239

If the valence band and conduction band of a solid overlap at low temperature, the solid may be

(a) a metal

(b) a semiconductor

(c) an insulator

(d) none of these

Explanation: Overlap of valence and conduction bands allows free carrier motion characteristic of metals.

#2240

Use the Mayer and Jensen nuclear shell model with spin-orbit interaction to figure out the spin of the 15_O nuclide:

(a) 5/2

(b) 1/2

(c) 7/2

(d) 3/2

Explanation: The ground-state spin of 15O is 1/2 (mirror to 15N), so option C is the correct nuclear spin assignment.

May 2024 Current Affairs MCQs & Solutions