Kpk Physics 2013 — Solved MCQs

Question 1

The energy stored in a charged capacitor is given by

Accepted Answer

B. ﻿U=1/2​CV2 — The energy (U) stored in a charged capacitor is given by the formula: U=1/2​CV2Where:C is the capacitance of the capacitor.V is the voltage across the capacitor.So, the correct option will be 1/2 CV². This formula tells us that the energy stored in a capacitor is directly proportional to the square of the voltage across it and the capacitance of the capacitor itself.

Question 2

The negative of the potential gradient is

Accepted Answer

B. Electric field intensity — The negative of the potential gradient is the Electric Field Intensity.In physics, the electric field is a vector field that shows the direction that a positively charged particle will move when placed in the field. The electric field is defined mathematically as the electric force per unit charge. The potential gradient is a measure of how the electric potential changes with respect to the spatial coordinates. When you take the negative of this, you get the direction of the electric field. This is because the electric field always points from regions of high potential to regions of low potential.

Question 3

A wire of uniform cross section "A", Length "L" and resistance "R" is cut in two equal parts. The resistivity of each part is:

Accepted Answer

C. Remains the same — The resistivity of a material is a property that is independent of its shape or size. It’s a characteristic of the material itself. So, when you cut a wire into two equal parts, the resistivity of each part remains the same as the original wire.The formula for resistance is given by: R = ρ L/Awhere:R is the resistance,ρ (rho) is the resistivity,L is the length of the wire, andA is the cross-sectional area of the wire.When the wire is cut into two equal parts, the length of each part becomes L/2, but the resistivity (ρ) and the cross-sectional area (A) remain the same. Therefore, the resistivity of each part is still ρ.

Question 4

Joule's law for heat dissipation in Resistance "R" carrying Current "I" is given by:

Accepted Answer

A. W = I2Rt — Joule’s law of electric heating states that the heat dissipated in a resistor is directly proportional to the square of the current passing through it, the resistance it offers to the current, and the time for which the current is passed. It can be mathematically expressed as: W = I2RtWhere:I is the current through the resistor (in amperes),R is the resistance (in ohms), andt is the time for which the current is passed (in seconds).

Question 5

The resonance frequency of LCR series circuit is:

Accepted Answer

C. 1/ 2π√LC — The resonance frequency (f) of an LCR series circuit is given by the formula: f = 1/ 2π√LCWhere:L is the inductance of the inductor measured in henries (H),C is the capacitance of the capacitor measured in farads (F),f is the resonance frequency measured in hertz (Hz).This formula gives the frequency at which the circuit will resonate, i.e., the frequency at which the inductive and capacitive reactances are equal, thereby causing the impedance of the circuit to be minimum. At this frequency, the circuit allows maximum current for a given applied voltage. It’s a fundamental concept in the study of AC circuits.

Question 6

The unit of magnetic flux density is:

Accepted Answer

A. Wb.m-2 — The unit of magnetic flux density is indeed expressed as Weber per square meter (Wb.m-2).

Question 7

One Pascal = Pa =

Accepted Answer

A. Nm-2 — The Pascal ( Pa) is the unit of pressure in the International System of Units (SI). It is defined as one newton per square metre (N/m²). 1 Pascal (Pa) = 1 Newton per square meter (N/m²)

Question 8

The rest mass of photon is:

Accepted Answer

B. Zero — The rest mass of a photon is 0. This is because photons are particles of light and they always move at the speed of light in a vacuum. According to the theory of relativity, any particle that moves at the speed of light must have zero rest mass. Therefore, the rest mass of a photon is 0.m0​=0where (m0) is the rest mass of the photon.

Question 9

Irms is equal to:

Accepted Answer

A. 0.707 I0 — For a sinusoidal wave, the RMS value is approximately 0.707 times the peak value (Imax). As: Irms = 0.707IoThis factor, 0.707, is the square root of 1/2, and it comes from the mathematical process used to calculate the RMS value.

Question 10

The device that stores electrical energy into magnetic field is called _.

Accepted Answer

B. Inductor — The device that stores electrical energy into a magnetic field is called an inductor. An inductor has the capability to store energy in its magnetic field.

Question 11

Shunted Galvanometer is called

Accepted Answer

B. Ammeter — A shunted galvanometer can be referred to as an Ammeter. This is because a shunt, which is a low resistance path, is connected in parallel to the galvanometer to allow it to measure current without being damaged by high currents. The shunt effectively diverts the majority of the current away from the galvanometer’s sensitive coils, allowing it to function as an ammeter.

Question 12

A diode consists of _.

Accepted Answer

A. One junction — A diode typically consists of one junction. It’s a two-terminal electronic component that conducts current primarily in one direction. The device is made up of a piece of semiconductor material with a P-N junction attached to two electrical terminals. The P-N junction refers to the boundary between the two types of semiconductors, “P” (positive) and “N” (negative). The junction allows current to flow more easily in one direction than the other, which is a fundamental property of a diode.

Question 13

When a charged particle is projected perpendicular to a uniform snape magnetic field, it's trajectory is

Accepted Answer

A. A circle — When a charged particle is projected perpendicular to a uniform magnetic field, its trajectory is a circle. This is due to the Lorentz force which acts as a centripetal force, causing the particle to move in a circular path. The radius of the circle can be determined by the equation: r = mv / qBwhere:m is the mass of the particle,v is the velocity of the particle,q is the charge of the particle, andB is the magnetic field strength.The direction of motion is given by the right-hand rule. If the thumb of the right hand points in the direction of the velocity of the positive charge and the fingers in the direction of the magnetic field, then the force (and hence the acceleration) is in the direction of the palm. For a negative charge, the force is in the opposite direction. This is why the charged particle moves in a circular path.

Question 14

De- Broglie suggested that every material particle has a wave length associated with it, given by

Accepted Answer

B. λ = h/mv — According to Louis de Broglie, every material particle has an associated wavelength, which is given by the de Broglie equation: λ = h/mvHere, ( λ ) is the wavelength, ( h ) is Planck’s constant, and ( p=mv) is the momentum of the particle.

Question 15

An 'a' particle has the charge _.

Accepted Answer

B. +2e — An ‘a’ particle, also known as an alpha particle, has a positive charge. Specifically, it has a net electrical charge of +2e. This is because an alpha particle is identical to the nucleus of the helium-4 atom, consisting of two protons and two neutrons bound together. Since protons carry a positive charge, the absence of electrons in an alpha particle results in a net positive charge.

Question 16

Wein's formula is:

Accepted Answer

A. mt = constant — It refers to the product of the maximum wavelength (m) at which the intensity of radiation is maximum, and the absolute temperature (T) of the black body. This product is a constant.

Question 17

Mathematical form of the uncertainty principle is

Accepted Answer

C. Δx × Δp = h / 4π — This equation: Δx × Δp = h / 4πis known as the Heisenberg Uncertainty Principle. It’s a fundamental concept in quantum mechanics that states it is impossible to simultaneously measure the exact position. The more precisely one of these values is known, the less precisely the other can be known.

Question 18

Velocity of light is given by

Accepted Answer

A. c = 1 / √ε0 μ0 — The speed of light in a vacuum, denoted by "c" is indeed given by the equation c = 1 / √ε0 μ0where;ε0​ is the permittivity of free space.μ0​ is the permeability of free space.

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