Kpk Physics 2023 — Solved MCQs

Question 1

Self inductnance (L) in terms of magnetic flux (¢), no of turns(N) and electric current (I) can be written as_.

Accepted Answer

B. L=N¢I — Self inductance (L) in terms of magnetic flux (¢), no of turns(N) and electric current (I) can be written as: L=N¢/I

Question 2

The ratio of power in AC circuit to that of DCcircuit is equal to_

Accepted Answer

C. Tan θ — Explanation will be added soon

Question 3

Pair product cannot take place in vaccum because_is not conserved.

Accepted Answer

D. Both energy and momentum. — Pair production, also known as pair creation, cannot take place in a vacuum because both energy and momentum are not conserved in such a process. Here’s a detailed explanation:Energy Conservation: For pair production to occur, a photon (or another high-energy particle) must convert into a particle-antiparticle pair (such as an electron and a positron). The energy of the incoming photon must be at least equal to the combined rest mass energy of the particle-antiparticle pair. However, even if this condition is met, energy conservation alone is not sufficient for pair production to occur in a vacuum.Momentum Conservation: The more critical issue in a vacuum is the conservation of momentum. In a vacuum, a single photon cannot simply convert into a particle-antiparticle pair without violating momentum conservation laws. This is because a photon has momentum but no rest mass, whereas the produced particles have both rest mass and momentum. The momentum of the photon cannot be split into two particles without some external object to balance the equation.In other words, if pair production were to occur in a vacuum, the initial photon momentum would need to be equal to the vector sum of the momenta of the resulting particle and antiparticle. Since there is no other object to absorb the excess momentum in a vacuum, this condition cannot be satisfied.Therefore, for pair production to occur, the presence of a nearby object, such as a nucleus or another particle, is required to take up the excess momentum, ensuring both energy and momentum conservation.

Question 4

An electric charge q is Placed at the centre of cube of side ‘a’ the electric flux on its one side will be _

Accepted Answer

C. q/6ε0 — Explanation will be added soon

Question 5

A/zX=A-4/z-2Y+Q The given reaction is completed by_

Accepted Answer

A. Alpha 𝜶 — The given nuclear reaction equation A/zX=A-4/z-2Y+Q is completed by an alpha particle emission. Here’s the reasoning:- The initial nucleus X has a mass number A and an atomic number Z .- The final nucleus Y has a mass number A-4 and an atomic number Z-2 .Therefore, the reaction is completed by the emission of an alpha particle.

Question 6

By increasing applied anode voltage, wavelength (A) of X rays_

Accepted Answer

C. Decreases — By increasing the applied anode voltage, the wavelength (λ) of the produced X-rays decreases.As,K.E = eVWhen the anode voltage in an X-ray tube is increased, the kinetic energy of the electrons striking the anode increases. This higher kinetic energy results in the production of higher-energy X-rays.E=hc/YSince higher energy corresponds to shorter wavelength, increasing the applied anode voltage leads to the generation of X-rays with shorter wavelengths.

Question 7

The seismometer works on the principle of_

Accepted Answer

A. Electromagnetism — A seismometer uses the principle of electromagnetism to convert the relative motion (caused by inertia) between a suspended mass and the frame into an electrical signal that can be measured and analyzed.

Question 8

98238 U contains_ number of nucleons.

Accepted Answer

B. 238 — Explanation will be added soon

Question 9

For one complete cycle, the simple mean value of AC cycle is_

Accepted Answer

A. Zero — The mean average value of alternating current (or emf) during a half, cycle is given by Im = 0.636 I0 or Em = 0.636 E0During the next half cycle, the mean value of ac will be equal in magnitude but opposite in direction.For this reason the average value of ac over a complete cycle is always zero. So the average value is always defined over a half cycle of ac.

Question 10

“mho” is a unit of_

Accepted Answer

A. Resistivity — Explanation will be added soon

Question 11

The function of unipolar junction transistors depends on_

Accepted Answer

A. Majority carriers — Unipolar junction transistors operate based on the majority charge carriers.

Question 12

The super conductor has a_resistance.

Accepted Answer

C. Zero — In a superconductor, the electric resistance is equal to zero. This is why an electric current can circulate forever in a superconducting ring even when the battery has been unplugged! This is how magnetic fields are created in MRIs.

Question 13

How much voltage is required to make 2A flow through a resistance of 80 Ω?

Accepted Answer

C. 160AΩ — How much voltage is required to make 2A flow through a resistance of 80 Ω?as V = IR,PUTTING VALUESV = 2 * 80V = 160V or 160AΩ

Question 14

Which of the given is a boson?

Accepted Answer

A. Photon — Photon is an example of boson.

Question 15

The reverse process of x-rays Production car be related to_

Accepted Answer

B. Photoelectric effect — In photoelectric effect, the photon having the energy greater than the work function of the material when strikes the material, the electron gets knocked out from the inner shell of the atom. Thus, we can say that it is the reverse process of production of continuous X-ray

Question 16

Volt per meter is a non Sl unit of _

Accepted Answer

D. Electric intensity — V/m is equilent to N/C which is the unit of electric field or electric intensity

Question 17

Charge to mass ratio of electron is_that of proton.

Accepted Answer

B. Greater than — Charge to mass ratio of electron is greater than that of proton because proton is 1837 times heavier than electron and e/m have inverse relation with mass.

Question 18

According to wein"s displacement law with rise in temperature of black body,the product λmaxT is_

Accepted Answer

D. None of these — The product of λmaxT is always constant.﻿λmaxT = 2.9 × 10−3 m K

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