Physics: CUET Mock Test - 3 - CUET MCQ

If the normal points in the opposite direction of the field, then θ = 180^o and the flux is taken as negative. If the magnetic field is pointing opposite the direction of the surface area then the value of this flux is negative.

The relationship between resistivity and temperature for a semiconductor material is given by the following equation:

s =

where s₀ is the resistivity at absolute zero temperature, Eg is the bandgap energy of the semiconductor material, k is Boltzmann's constant, and T is the temperature in Kelvin.

• This equation is known as the Arrhenius equation and describes the temperature dependence of the resistivity of semiconductors.
• As the temperature increases, the resistivity of a semiconductor decreases exponentially due to the increasing number of thermally excited charge carriers (electrons and holes).
• Since, the decay is exponential, the resistivity decreases as the temperature increases.
• So, the graph representing resistivity vs temperature would be exponential decay and represented by,

The correct answer is option (c)

Concept:

The radius of the trajectory of a charged particle moving in a uniform magnetic field is given by the formula:

r = (mv)/(qB)

where:

r is the radius of the trajectory
m is the mass of the particle
v is the velocity of the particle
q is the charge of the particle
B is the magnetic field strength
The ratio of the radii of the trajectories of a proton and an alpha particle can be found by dividing their respective radii:

r_(proton) / r_(alpha) = [(m_protonv_proton)/(q_protonB)] / [(m_alphav_alpha)/(q_alphaB)] ------(1)

Since both particles have the same kinetic energy, we can use the fact that the kinetic energy of a particle is given by:

K = (1/2)mv²

Thus, we have:

v_proton =
v_alpha =

Substituting these expressions into the ratio of radii equation(1),and Plugging in the values for the masses and charges of the particles, we get

r(proton) / r(alpha) = [(1/4)*(2/1)]*sqrt(4/1) = 1/2 * 2 = 1

Therefore, the ratio of the radii of the trajectories of the proton and the alpha particle is 1:1 or simply 1.

This means that the radii of their trajectories will be the same.

The correct answer is option (1)

Concept:

• When an electron is projected in a uniform magnetic field along the direction of the field lines, the electron will experience a force perpendicular to both its velocity and the magnetic field direction, known as the Lorentz force.
• The direction of the Lorentz force can be determined using the "right-hand rule."

Right-hand rule:

• Point your right thumb in the direction of the electron's velocity, point your fingers in the direction of the magnetic field, and the direction in which your palm faces gives you the direction of the force experienced by the electron.
• Since the velocity and magnetic field are both along the same direction, the angle between them is 0 degrees. Therefore, the force experienced by the electron will be zero, and the electron will continue to move along its original path without any deviation

The correct answer is option (3).

Concept:

• Plano- concave lens: It is the type of lens that has one side as a plane surface and the other side as a concave lens.
• Its focal length is always negative.
• The power of a lens is specified as the inverse of the focal length in meters, or P/1/f

Explanation:

Given, focal length, f = 10 cm = 0.1 m

Then power of the lens is P = 1/f = 1/0.1 = 10 D

• When the lens is cut in to two equal parts then there will be no effect on focal length as the radius of curvature will remain same and then the focus will be same.
• Then the power of each part is equal to the original lens.
• P = 10 D

The correct answer is option 1):(Iron)

Concept:
Semiconductor:

• A semiconductor is a substance that has resistivity in between the conductor and insulator.
• A semiconductor has 4 valance electrons that are C, Si, Ge, Sn, and Pb,Te
• Here Iron is not a semiconductor.It is a conductor
• Type of semiconductors are

• Semiconductors that are chemically pure, in other words, free from impurities are termed as intrinsic semiconductors
• Extrinsic semiconductors are semiconductors that are doped with specific impurities. The impurity modifies the electrical properties of the semiconductor and makes it more suitable for electronic devices such as diodes and transistors

Concept:

• The Refractive index also called the index of refraction measures the bending of a ray of light when passing from one medium into another.

• If i is the angle of incidence of a ray in vacuum (the angle between the incoming ray and the perpendicular to the surface of a medium, called the normal) and r is the angle of refraction (the angle between the ray in the medium and the normal),
• Then the refractive index n is defined as the ratio of the sine of the angle of incidence to the sine of the angle of refraction.
• 
• Refractive index of combined media = --- (1)
• Critical angle, C = sin^-1(μ^-1) --- (2)

Calculation:

Given, the refractive index of water,

Refractive index of a glass slab,

Refractive index of combined media =

From equation 1,

From equation 2 Critical angle,

Electric dipole moment:

• The electric dipole moment is a measure of the separation of positive and negative electrical charges.
• It consists of two equal and opposite charges that are infinitely close together.
• Its magnitude is equal to the product of the charge and the distance between the charges and having direction from the negative to the positive charge along the line between the charges.

Electric dipole moment p = qd

Where,

q = charge (Coulomb)

d = distance between charges (meter)

Concept:

Young's double slit experiment

• In the double slits experiment, we use two long parallel slits as the sources of light in place of pin holes.
• The light coming out of the two slits is intercepted on a screen placed parallel to the plane of the slits.
• The slits are illuminated by a parallel beam of a monochromatic light.
• A series of dark and bright strips, called fringes, are observed on the screen.
• The fringe-width is given by,
• Where, β = fringe width, λ = wavelength of light, D = distance of screen from slits, d = distance between slits.

Calculation:

Given, λ = 5898 Å, number of fringes = 92

Let the length of the screen on which the fringes are obtained be L₀
​⇒ 92 × β₁ = L₀

⇒
⇒

⇒ --- (1)

Now for λ = 5461 Å, Let the number of fringes = n

⇒ β₂ = --- (2)

From equation 1, and 2

⇒

⇒ n = 99

Potentiometer measures the potential difference using null deflection method, where no current is drawn from the cell; whereas voltmeter needs a small current to show deflection. So, accurate measurement of p.d is done using a potentiometer.

• Copper is a conductor and we know that for conductors, resistance is directly proprtional to temperature. Therefore on decreasing temperature resistance also decreases.
• Whereas, germanium is a semiconductor and for semiconductors, resistance is inversely proportional to temperature.
• So on decreasing temperature resistance increases.

In electromagnetic waves the ratio of amplitudes of electric field and magnetic field is equal to the velocity of the electromagnetic waves in free space.

(E₀ / B₀) = c

Electromagnetic waves are used in various applications such as:

• Detecting invisible writing (UV light)
• Keeping plants warm in greenhouses (infrared radiation)
• Enhancing vision in warfare (thermal imaging)

However, global warming is primarily caused by greenhouse gases trapping heat. This process involves electromagnetic waves indirectly through the greenhouse effect. Therefore, while electromagnetic waves contribute to the mechanisms of global warming, they are not directly used in the phenomenon itself.

Thus, option B is correct as it represents an effect rather than a direct application.

Red light has the lowest energy and is least scattered and has thus least frequency, thus we get that it has the largest wavelength. Similarly violet has maximum frequency.

V(velocity/speed)= ω/wave number (K)
V= 12×10¹⁵/4×10⁷
V=3×10⁸ m/s

For a full-wave rectifier,

Form factor = I_rms/I_dc
Form factor = 
Form factor =  1.11

Transformers are used to convert low alternating voltage to a high alternating voltage and vice versa. Transformers are based on the phenomena of mutual induction. A transformer consists of a soft iron coil with two coils wound around it which are not connected to one another. The other statements are not valid.

Length (L) = 0.7 m; Speed (v) = 1 m/s; Magnetic field (B) = 20 T
The required equation E = -vLB (The negative sign only applies to the direction)
E = 1 × 0.7 × 20
E = 0.7 × 20
E = 14 V
Therefore, the motional emf in the bar and rails is 14 V.

For a purely inductive circuit, Φ = ± (π/2)
Power factor = cos (±(π/2))
Power factor = 0
Therefore, the power factor will be minimum for an inductive circuit.

Instantaneous power is defined as the power in an AC circuit at any instant of time. It is equal to the product of values of alternating voltage and alternating current at that time. And, because instantaneous power varies in both magnitude and sign over a cycle, it seldom has any practical importance.

L = 0.15 m; B = 40 T; v = 5 m/s; R1 = 20 Ω; R2 = 20 Ω; R3 = 5 Ω
Emf (E) = vLB = 5 × 0.15 × 40
E = 5 × 6
E = 30 V
R1 and R2 are in parallel ➔ 
R_TOT = R + R3 = 10 + 5 = 15 Ω
Therefore, current (I) = E/R
I = 30/15
I = 2 A

Average power can be defined as the power averaged over one full cycle of alternating current. It is also known as true power. The expression for average power is given by:
P_av=V_rmsI_rmscos⁡Φ = (V₀I₀/2)(cosΦ)

When light passes from a rarer to a denser medium, the wavelength of light changes but the frequency remains unchanged. Therefore, there is no change in the frequency of light, only the wavelength changes.

The power factor of an AC electrical power system is defined as the ratio of the real or true power absorbed by the load to the apparent power flowing in the circuit, and in the closed interval of −1 to 1. The expression for power factor is given as:
cos⁡Φ = (True power/Apparent power)

Absolute refractive index = (Speed of light in vacuum/Speed of light in the medium). The relative refractive index of water with respect to glass is less than unity.

Given: B = 0.5 T; v = 70 cm/s = 70 × 10^-2 m/s; L = 45 cm = 45 × 10^-2 m; R = 10 Ω
Motional emf (E) = vLB = 70 × 10^-2 × 45 × 10^-2 × 0.5
E = 0.15 V
Current (I) = E/R
I = 0.15/10
I = 0.015 A
Rate of energy or power (P) = I²R
P = 0.015² × 10
P = 2.25 × 10^-3 W
Therefore, the rate of energy transfer is 2.25 × 10^-3 W.

Conductors have low resistivities in the range of 10^-8 Ωm to 10^-6 Ωm. Metals are good conductors. Conductors are objects or types of material that allows the flow of charge in one or more directions, and a result, the resistance offered against the flow of charge will be less.

A circuit containing only a pure resistance in an AC circuit is known as a pure resistive AC Circuit. For a purely resistive circuit, the power factor is one, because the reactive power equals zero, i.e.
Φ = 0 → Power factor (cos⁡0)=1

Insulators are materials which do not conduct electric current, and thereby, offer high resistance to the flow of charges. Insulators like bakelite and hard rubber have very high resistivities in the range of 10¹⁴ to 10¹⁶ Ωm.