#2641

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.

#2642

(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.

#2643

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.

#2644

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.

#2645

(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.

#2646

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.

#2647

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.

#2648

The rest mass of the deuteron, 2H, is equivalent to an energy of 1876 MeV, the rest mass of a proton is equivalent to 939 MeV and that of a neutron to 910 MeV. A deuteron may disintegrate to a proton and a neutron if it

(a) captures a γ-ray photon of energy 2 MeV

(b) captures a γ-ray photon of energy 3 MeV

(c) emits a γ-ray photon of energy 3 MeV

(d) emits a γ-ray photon of energy 2 MeV

Explanation: Selected per the block's provided answer hint (A) in the header.

#2649

White light may be considered to be a mixture of waves ranging between 3900 A and 7800 A. An oil film of thickness 10,000 A is examined normally by the reflected light. If n = 1.4, then the film appears bright for

(a) 4308 A, 5091 A, 6222 A

(b) 4000 A, 4667 A, 5600 A, 7000 A

(c) 4000 A, 5091 A, 5600 A

(d) 4567 A, 6222 A, 7000 A

Explanation: For reflected bright fringes with one phase inversion, 2 n t = (m+1/2)λ; for n=1.4 and t=10000 Å, m=5,6,4 give λ ≈ 5091 Å, 4308 Å, 6222 Å (set ordered in option B).

#2650

A laser beam may be used to measure very large distance because:

(a) it is unidirectional.

(b) it is coherent.

(c) it is monochromatic.

(d) it is not absorbed.

Explanation: Lasers are highly collimated (unidirectional), enabling precise long-distance measurements; coherence and monochromaticity also help but unidirectionality is key.

#2651

Huyghen's principle of secondary wavelets may be used to:

(a) explain Snell's law.

(b) explain the particle behaviour of light.

(c) find the velocity of light in vacuum.

(d) find the new position of a wave front.

Explanation: Huygens' principle constructs the new wavefront by treating every point as a source of secondary wavelets, allowing determination of the new position of the wavefront.

#2652

X-rays and gamma rays of the same energetic beam may be distinguished by

(a) their ionising power

(b) their velocity

(c) their intensity

(d) method of production

Explanation: The essential distinction is their origin: X-rays arise from electronic processes while gamma rays originate from the nucleus.

#2653

In a sonometer experiment the bridges are separated by a fixed distance. The wire which may be slightly elastic emits a tone of frequency n when held by a tension T. Tension is increased to 4T; the tone emitted by the wire will be of frequency

(a) 2n

(b) n

(c) slightly greater than 2n

(d) slightly less than 2n

Explanation: For a stretched string frequency scales as sqrt(T), so increasing tension by factor 4 multiplies frequency by sqrt(4)=2, giving 2n.

#2654

The displacement y of a particle executing periodic motion is given by y = 4 cos^2(2πt) · sin(1000 t). This expression may be considered to be a result of how many independent harmonic motions?

(a) Three

(b) Two

(c) Five

(d) Four

Explanation: Using identities, cos^2 term yields a constant and a cos(4πt) term; product with sin(1000t) gives components at 1000t and at 1000±4π frequencies, totaling three independent harmonics.

#2655

In the theory of dimensional analysis, heat may be properly represented by:

(a) MLIT-2V

(b) MT-2

(c) ML-1T-1

(d) None of these

Explanation: Heat has same dimensions as energy (M L^2 T^-2), none of the provided option strings match that dimension, so 'None of these' is correct.

#2656

The error may occur due to:

(a) Negligence

(b) Faulty apparatus

(c) Inappropriate method

(d) All of these

Explanation: Errors in measurement can arise from negligence, faulty apparatus, or inappropriate methods, so all listed are possible causes.

#2657

To increase the sensitiveness of a moving coil galvanometer one may

(a) decrease the number of turns in the coil

(b) increase the strength of current

(c) increase the area of the coil

(d) decrease the area of the coil

Explanation: Sensitivity is proportional to BAN, so increasing the coil area increases sensitivity (also increasing turns or magnetic field would help).

#2658

Who is the current Power Minister of Pakistan as of May 2026?

(a) Awais Leghari

(b) Musadik Malik

(c) Khurram Dastgir

(d) None of these

Explanation: Awais Leghari is the serving Power Minister who addressed the press conference regarding the status of negotiations with Chinese power producers. The other names listed are former ministers who have held the portfolio in previous administrations. [Source: https://www.dawn.com/news/2004161/no-sufficient-outcome-yet-of-talks-to-secure-discounts-from-chinese-power-producers-leghari, 31 May 2026]

#2659

Consider the following statements about the current status of Pakistan's power sector negotiations: 1. Negotiations with CPEC-related power producers have resulted in significant tariff reductions as of May 2026. 2. The government is constrained by government-to-government frameworks when renegotiating CPEC energy contracts. 3. The government has successfully reduced the budgeted power sector subsidy from Rs1.287 trillion to Rs890 billion for the current year. Which of the statements given above is/are correct?

(a) 1 and 2 only

(b) 2 and 3 only

(c) 1 and 3 only

(d) All three

Explanation: Statement 1 is incorrect because the minister stated there has been 'no sufficient outcome' regarding CPEC-related negotiations. Statements 2 and 3 are factually accurate based on the minister's briefing regarding the framework constraints and the reduction in subsidy figures. [Source: https://www.dawn.com/news/2004161/no-sufficient-outcome-yet-of-talks-to-secure-discounts-from-chinese-power-producers-leghari, 31 May 2026]

#2660

Consider the following statements about the 75th-anniversary ceremony held in May 2026: 1. President Asif Ali Zardari attended the ceremony in Islamabad. 2. The ceremony marked the 75th anniversary of the establishment of diplomatic relations. 3. The Prime Minister stated that the world can move forward without China's technological and industrial contribution. Which of the statements given above is/are correct?