Physics: CUET Mock Test - 3 - JEE 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.

Motional electromotive is the emf induced by the motion of the conductor across the magnetic field. The expression for motional electromotive force is given by:
E = -vLB
This equation is true as long as the velocity, magnetic field, and length are mutually perpendicular to each other. The negative sign is associated with Lenz’s law.

The reactance of an inductor in a dc circuit is zero.
For dc → f = 0
X_L = 2π f L
X_L = 0
Therefore, the reactance of an inductor in a dc circuit is zero.

In an AC circuit, we can define three types of power, namely, Instantaneous power, Average power, and Apparent power. A circuit element produces or dissipates power according to the equation → P = IV, where I is the current through the element and V is the voltage across it.

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.

Factors on which the angle of deviation depends are → the angle of incidence, the material of the prism, the wavelength of light used, and the angle of the prism. So, the factor on which the angle of deviation that does not depend on is the angle of reflection.

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.

Refractive index of the prism material is μ = 

μ = √3.

L = 0.15 m; B = 40 T; v = 5 m/s; R1 = 10 Ω; R2 = 10 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

When the frequency of an ac is doubled → The inductive reactance (X_L) gets doubled.
This is because inductive reactance is directly proportional to the frequency of an alternating current circuit.

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)

For a step-up transformer, the voltage at the second terminal is greater than the primary terminal, i.e. → V_s > V_p. Similarly, the current in the secondary coil is lesser than that current flowing the primary coil, i.e. → I_s < I_p. Also, the number of turns in the secondary winding is greater than that in the primary winding, i.e. → N_s > N_p. So the transformation ratio will be greater than 1. So, the correct combination is given as:
k > 1; V_s > V_p, I_s < I_p, N_s > N_p

The reason is that for a given angle f incidence, the reflection is the same for all the wavelengths of white light while the angle of refraction is different for different wavelengths. Therefore, this is how dispersion is caused.

Van de Graff generator is used to create a large amount of static electricity. A Van de Graff generator uses static electricity and a moving belt to charge a large metal sphere to a very high voltage. As the belt moves, electrons move from the rubber belt to the silicon roller, causing the belt to become positively charged and the roller to become negatively charged. As a result, it builds up positive charge.

f = X_L/2πL
f = 3500/(2×3.14×2.5)
f = 222.9 Hz ≈ 223 Hz
Therefore, the frequency of a coil having reactance of 3500 Ω is 223 Hz.

A Van de Graff generator, by means of a moving belt and suitable brushes, transfers charge continuously to a large spherical conducting shell. As a result, a potential difference of the order of several million volts is built up and this can be used for accelerating charged particles.

Van de Graff generator was invented by Robert Jemison Van de Graff on November 28, 1933. Robert Jemison invented the Van de Graff generator, which is a kind of high-voltage electrostatic generator that accelerates particles, while he was doing his PhD in Princeton University.

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.

Given: L = 2 m; B = 50 T;
The bar is said to be falling freely, so → u = 0
According to Newton’s third equation → v² – u² = 2gh
v² = 2gh; h = 40 m

v = 28 m/s
Motional emf (E) = vLB
E = 28 × 2 × 50
E = 2800 V

For dc, f = 0,
X_L = 2π f L
X_L = 0
X_L is zero for dc and has a finite value for ac Hence an inductor offers an easy path to dc and a resistive path to ac.

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)

For a step-down transformer, the voltage at the second terminal is lesser than the primary terminal, i.e. → V_s < V_p. Similarly, the number of turns in the secondary winding is lesser than that in the primary winding, i.e. → N_s < N_p. Also, the current in the secondary coil is greater than that current flowing the primary coil, i.e. → I_s > I_p. So the transformation ratio will be lesser than 1. So, the correct combination is given as:
k < 1; V_s < V_p, I_s > I_p, N_s < N_p

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

Core of a transformer is used to transfer the flux produced by primary coils of transformer to secondary coils of a transformer. Therefore, the core of a transformer is made of soft iron because it has high permeability so it provides complete linkage of magnetic flux of the primary coil to the secondary coil.

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.