Kpk Physics 2020 — Solved MCQs

Question 1

Potential difference between two points in an electric field is _ when 600 J energy moves a charge of 2C.

Accepted Answer

C. 300 V — As,K.E = eVwe need to calculate the potential difference (V),V= KE/eV = 600/2V = 300V

Question 2

The dielectric material are made up of _ type of moelcules.

Accepted Answer

A. Two — As the name shows, dielectric is made up of two types of molecules

Question 3

The restivity of lead is _ μΩm.

Accepted Answer

B. 0.219 — The resistivity of lead is 22μΩm.

Question 4

The temperature co-efficient of a thermistor can be _.

Accepted Answer

D. Both B and C — The temperature co-efficient of a thermistor can be positive (Metals) as well as negative (Semiconductors) .

Question 5

One weber per square meter is equal to _.

Accepted Answer

C. 1 Tesla — One weber per square meter is equal to one tesla.The tesla (T) is the unit of magnetic flux density (or magnetic induction) in the International System of Units (SI). It is defined as the magnetic flux through a square meter (m²) of a perpendicular plane.

Question 6

The magnetic flux is maximum for θ=_

Accepted Answer

D. 0º — When the angle between magnetic field and area is 00 Φ = BA cos(00)as cos 00 is equal to 1.so ,Φ = BA

Question 7

In step-up transformer _

Accepted Answer

C. Ns>Np — In step-up transformer, no of turns in secondary coil is greater than no of turns in primary coil.Ns>Np

Question 8

When magnetic flux changes by 2 x 10^-2 Wb at ∆I=0.01 A then co-efficient of mutual inductance is _

Accepted Answer

D. 2H — ϕ=Midϕ=MdiM = dΦ/ dIM = 2×10-2 / 1×10−2M = 2H

Question 9

In a pure inductance current lags behind voltage by _

Accepted Answer

C. 90º — In a pure inductance, the current lags behind the voltage by 90 degrees or π/2

Question 10

Shear Modulus of copper is _

Accepted Answer

C. 4,4 x 10^10 pa — shear modulus of copper is 4,4 x 10^10 pa

Question 11

_ is an example of paramagnetic material.

Accepted Answer

B. Antimony — Paramagnetic materials: These materials, such as aluminum,antimony, platinum, and certain metal oxides, are weakly attracted by a magnetic field. They have unpaired electrons that align with the magnetic field but do not retain any magnetization when the external field is removed.

Question 12

A transistor consists of _ regions of doped semiconductor.

Accepted Answer

A. Two — Semiconductor is doped in 2 regions, Pentavalent impurities(N-type) and trivalent impurities (P-type)

Question 13

Pair production cannot take place in vacuum because _ is not conserved.

Accepted Answer

D. Energy and momentum — the pair production can not take place in space or a vacuum, as the energy and the momentum can not be conserved at the same time.

Question 14

If K.E of a free electron doubles, its de-Broglie wavelength changes by the factor _

Accepted Answer

D. 1/√2 — When the kinetic energy (KE) of a free electron doubles, its de Broglie wavelength changes by a factor of 1/√2.

Question 15

The _ series lies in the visible region of the spectrum.

Accepted Answer

D. Balmer — Lyman = UV regionBalmer = Visible regionPaschen,bracket, pfund = Infrared region

Question 16

In discharge tube of Helium-Neon laser _ Helium gas is filled

Accepted Answer

D. 90% — In a Helium-Neon (HeNe) laser, the mixture of gases typically consists of approximately 10% helium (He) and 90% neon (Ne).The primary lasing transition in a HeNe laser occurs in the neon atoms, which provide the optical gain necessary for laser operation. Helium is added to the gas mixture to assist in the excitation process and to help stabilize the discharge.Therefore, in the discharge tube of a Helium-Neon laser, approximately 10% of the gas is helium.

Question 17

Unit of decay constant "λ" is _

Accepted Answer

D. S^-1 — Unit of decay constant "λ" is s-1as decay constant = 0.693/T

Question 18

The amount of radioactive isotope _ with time.

Accepted Answer

B. Decreases — The amount of a radioactive isotope decreases with time due to its natural process of radioactive decay. This decay occurs spontaneously, emitting radiation and transforming the nucleus of the isotope into a different nuclide.The rate at which the radioactive isotope decreases over time is described by its half-life. Each radioactive isotope has a characteristic half-life, which is the time it takes for half of the initial quantity of the isotope to decay.As time progresses, the amount of the radioactive isotope continues to decrease exponentially, following the decay curve described by its half-life.

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