Physics: CUET Mock Test - 4 - CUET MCQ

Given: Output power (P_o) = 100 W; I_p = 0.5 A; V_p = 250 V
Input power (P_i) = V_p × I_p
P_i = 250 × 0.5 = 125 W
Efficiency = (Output power/Input power) × 100%
Efficiency = (100/125) x 100
Efficiency = 80
Therefore, the efficiency of the transformer is 80%.

Concept:

• To convert a galvanometer into an ammeter, a shunt resistor is connected in parallel with the galvanometer.
• A shunt resistor is a low resistance wire or a coil that is connected in parallel with the galvanometer to divert most of the current away from the galvanometer.
• The shunt resistor is designed to have a very low resistance so that most of the current flows through it instead of the galvanometer.
• By connecting the shunt resistor in parallel with the galvanometer, the total current is split between the shunt resistor and the galvanometer.
• The amount of current that flows through the galvanometer is then proportional to the voltage drop across it.
• By selecting an appropriate value for the shunt resistor, the current that flows through the galvanometer can be kept within its range, and the galvanometer can be used as an ammeter to measure higher currents.

The value of the shunt resistor is selected such that the full-scale deflection of the galvanometer occurs when the maximum current to be measured flows through the ammeter. The value of the shunt resistor is calculated using the following formula:

Rs =

where:

Rs is the resistance of the shunt resistor
G is the resistance of the galvanometer
I_g is the full-scale deflection current of the galvanometer
I_m is the maximum current to be measured by the ammeter
The shunt resistor should have a very low resistance compared to the resistance of the galvanometer to ensure that most of the current flows through it.

The value of the shunt resistor should also be such that it can handle the maximum current to be measured without getting damaged or changing its resistance value

The correct answer is option (3).

​Statement I

• The electric field is produced by electric charges and is a measure of the force per unit charge that would be exerted on a test charge placed in the field.

Statement II

• Statement II is incorrect because a current element (I dl) is not a magnetic field, but rather it is an infinitesimal segment of current-carrying wire that produces a magnetic field.
• The magnetic field is a vector field that describes the influence of magnetic forces on moving charges or magnetic materials.

The correct answer is option (3).

​LASIK:

• LASIK (Laser-Assisted in Situ Keratomileusis) is a type of refractive surgery that uses a laser to correct vision problems.
• During the LASIK procedure, a surgeon uses a laser to reshape the cornea, which is the clear front part of the eye.
• The laser used in LASIK surgery is an ultraviolet excimer laser.
• Therefore, ultraviolet excimer laser rays are used in doing LASIK eye surgery.

So, the Ultraviolet rays are used in doing LASIK.
The correct answer is option (1).

Concept:

• Electromagnetic wave: It can also be said that electromagnetic waves are the composition of oscillating electric and magnetic fields.
• Electromagnetic waves are shown by a sinusoidal graph.
• It consists of time-varying electric and magnetic fields which are perpendicular to each other and are also perpendicular to the direction of propagation of waves.

• If the electric field oscillated in the x-axis, then the magnetic field will oscillate in the y-axis and the direction of propagation of the electromagnetic wave is in the z-axis.
• The speed of electromagnetic waves equals the speed of light in air.
• The relation between the magnitude of the electric field and the magnetic field is given as E0 = B0 c

Explanation:
Given,
The magnetic field in a plane electromagnetic wave, Bx = 2 × 10-7 sin (0.6 × 103y + 2 × 1011t) T.
Take, the speed of light, c = 3 ×108 ms-1
The relation between the magnitude of the electric field and the magnetic field is given as E0 = B0 c
E0 = 2 ×10-7 × 3 ×108
E0 = 60 V/m
So, the electric field in a plane electromagnetic wave is Ez = 60 sin (0.6 × 103y + 2 × 1011t) V/M.
The correct answer is option (4)

Concept:

Keeping the frequency constant of incident radiation,

• The number of photoelectrons emitted per second is proportional to the intensity of incident light .This relationship is known as the photoelectric effect.
• According to the photoelectric effect, when light of a certain frequency is incident on a metal surface, electrons are emitted from the metal surface.
• The number of electrons emitted is proportional to the intensity of the incident light.

This relationship is expressed by the equation:

I = K *I₀

Where I is the number of photoelectrons emitted per second, I₀ is the intensity of the incident light, and K is a proportionality constant known as the photoelectric constant.

This equation shows that the number of photoelectrons emitted per second increases with increasing intensity of the incident light. However, the maximum kinetic energy of the photoelectrons is only dependent on the frequency of the incident light, and is independent of the intensity of the light.

The correct answer is option (1)

CONCEPT
→ When an electron comes down from a higher state (n > 2) to n = 2 state, the e-m radiation emitted is called Balmer lines.
→ Visible spectrum lies in the range 380 to 700 nm. Only Balmer lines emit e-m radiation which lies in the visible spectrum.

So, the correct answer is option (2).

The correct answer is A.

Key Points

Number of turns of solenoid = N
∴ Number of turns per unit length is,
n = N/I
Where, l is the length of the solenoid.
Magnetic field inside the solenoid is,
B = μ0ni

The correct answer is 2Ω.
When resistors are connected in parallel, the formula for calculating the equivalent resistance is given by -

Given:
R₁ = 3 and R₂ = 6
Substituting given values and solving the above equation

R = 2Ω

Thus, the value of equivalent resistance when the resistors of 3 ohm and 6 ohm are parallel will be 2Ω.

CONCEPT:

• Davison Germer experiment was conducted in 1927 to study the wave nature of the electron.
• The electrons are emitted by an electron gun and are accelerated by applying a suitable potential difference between anode and cathode.
• The finely collimated beam is directed towards the Ni crystal.
• The scattered electrons are collected using a movable detector and a graph is plotted between applied potential and angle of reflection.
• Analysis of those graphs showed the wave nature of the electron.

EXPLANATION:

• The velocity of an electron accelerated through a potential is given by

Where e = Charge of electron and V_o = potential, m = mass of the particle

• From the above equation it is clear that

⇒ V ∝ √V_o

• The velocity of the electron is directly proportional to the square root of the potential difference between the anode and filament. Hence, option 2 is the answer

Concept:

​Magnetic flux:

• It is defined as the number of magnetic field lines passing through a given closed surface.
• It provides the measurement of the total magnetic field that passes through a given surface area.
  
• Formula, ϕ = BA cosθ , where B = magnetic field, A = area, θ = angle between the area and magnetic field
• The relation between the magnetic flux and current is given as, ϕ = LI, where L = self-inductance, I = current​

Calculation:
Given,
self inductance, L = 100 mH, current, I = 8 mA
The magnetic flux linked with each turn of the coil is given as,
ϕ = LI
ϕ = 100 × 10^-3 × 8 × 10^-3
ϕ = 8 × 10^-4 Wb
Hence, the magnetic flux linked with each turn of the coil is 8 × 10-4 Wb.

We know that, P_av = V_rms I_rms cos⁡Φ ……1 and cosΦ;= R/Z ....2
In LCR, cosΦ = V_R/V = IR/IZ and I_rms = V_rms/Z ....3
Substituting 2 and 3 in 1


Given: V_rms = 24 V; Resistance (R) = 70 Ω; Inductance (I) = 30 mH = 20 × 10^-3 H; Capacitance (C) = 300 μF
X_L = 2πυL = 2π (60)(30 × 10^-3)
X_L= 11.304 Ω
X_C = (1/(2πvC)) = (1/(2π(60)(300×10⁻⁶)))
X_C = 8.846 Ω
For series LCR circuit → Z = 

Z = 70.04 ≈ 70 Ω
So, the energy used in 1000 seconds is → P_avt =

Therefore, the energy dissipated in the circuit at 1000 seconds is 8.22 × 10³J.

Given: N_s = 20; N_p = 100; V_p = 120 V
For a step-down transformer → N_s/N_p = V_s/V_p

V_s = 24 V
Therefore, the voltage output from the secondary coil is 24 V.

Fringe width is given as:
β = Dλ/d
As the screen is moved closer to the two slits, the distance denoted by D decreases and so fringe width β increase.

According to Bohr’s second postulate, an electron revolves around the nucleus of an atom in orbits and, therefore, the angular momentum of the revolution is an integral multiple of (h/2p), where h is the Planck’s constant. Thus, the expression for angular momentum is given as: L = nh/2p

Lens is a portion of a transparent refracting medium bound by two spherical surfaces or one spherical surface and the other plane surface. Lenses are divided into two classes, namely, convex lens or converging lens, and concave lens or diverging lens.

On doubling the diameter, the area of the objective increases four times. Its light-gathering power increases four times. The brightness of the image also increases four times. Therefore, the intensity of the image increases by four.

λ = 589 nm, μ = 1.33.
Wavelength in water, λ_W = λ/μ
λ_W = 589/1.33
λ_W = 443 nm.

Fringe width is expressed as:
β = Dλ/d.
Since the wavelength are related as shown → λ_G < λ_Y < λ_O, we can say that → β_G < β_Y < β_O.

de – Broglie hypothesis did modify Bohr’s second postulate. This postulate of Bohr regarding the quantization of the angular momentum of an electron was further explained by Louis de Broglie. According to de – Broglie, a moving electron in its circular orbit behaves like a particle-wave.

When the lens is thicker in the middle than at the edges, then it is convex lens. When the lens is thicker at the edges than in the middle, then it is concave lens. Therefore, X = convex lens, and Y = concave lens.

The fly will not be seen in the final image. But the intensity of the final image gets reduced because light will not enter the telescope from that part of the object where the fly is sitting. Therefore, a reduction effect will be observed in the final image of the fly.

When a light wave enters from the air medium into the glass medium, the energy of the wave decreases because a part of the light wave is reflected in the air. Therefore, in this way, energy will be affected.

Fringe width is given as:
β = Dλ/d.
So β = (1×500×10⁻⁹)/(10⁻³)
β = 0.5 mm
Therefore, the fringe separation when blue-green light of wavelength 500 nm is used is 0.5 mm.

A string is used to represent the behavior of a particle analogously to the waves traveling on it. Particle waves can lead to standing waves held under resonant conditions. When a stationary string is plucked, it causes several wavelengths to be excited. But, we know that only the ones which have nodes at the ends will survive.

The resistivities of semiconductors lie between 10-6 Ωm and 104 Ωm. A semiconductor material has an electrical conductivity value falling between that of a conductor, such as metallic aluminum, and an insulator, such as wood. Silicon and germanium are typical semiconductors.

In a telescope, the objective should have a large focal length than the eyepiece. So the lens of 50 cm focal length will be used as the objective. So, the smaller one of the two, i.e. the 5 cm focal length lens will be used as the eyepiece.

When a wave undergoes refraction, the phase change will be zero. The phase change is what guides the process. Therefore, no phase change occurs to a wave during refraction.

Resultant intensity at the point of destructive interference will be as follows:
I = I₀ + I₀ + 2√I₀ I₀ cos 180^o
I = 0
Therefore, the value of the resultant intensity at a point of destructive interference is zero.

Given: number of turns (n) = 200 turns per meter; current (I) = 2 A; Relative permeability (µ_r) = 200
Magnetic intensity is given by: H = nI = 200 × 2 = 400 A/m
μ_r = 1 + γ → γ is the magnetic susceptibility of the material
γ = μ_r – 1
Magnetization → M = γ x H
M = (μ_r – 1) × H
M = (200 – 1) × 200
M = 199 × 200
M = 79600
M = 7.96 × 10⁴ A/m ≈ 8 × 10⁴ A/m