Physics: CUET Mock Test - 1 - CUET MCQ

The zone near a charge where its attraction or repulsion force works, is known as the electric field of that charge. Theoretically, it is up to infinite but practically it has limitations. If a unit positive charge is kept in that field, it will undergo some force which is known as electric field intensity at that point.

Concept:

Electric field:

• ​It is defined as the force per unit of positive charge.
• Formula, Electric field, E = F/q where F = force, q = positive charge
• The SI unit of electric charge is N/C.

Electric field due to an infinitely long straight wire:

• Consider an infinitely long straight, uniformly charged wire. Let the linear charge density of this wire be λ. P is the point that is located at a perpendicular distance from the wire. The distance between point P and the wire is r.

​

• The electric field is due to an infinitely long straight wire, .

Explanation:
Assuming the wire is infinitely long, the electric field will be radial and will have a magnitude given by:

E =

where
λ is the linear charge density of the wire,
ε₀ is the permittivity of free space,
r is the distance from the wire.

• The direction of the electric field will be radial and pointing away from the wire if the charge on the wire is positive and towards the wire if the charge on the wire is negative.
• Note that the above formula assumes that the wire is thin compared to the distance from it, and that the electric field is being measured at a point far away from the ends of the wire. If these assumptions are not satisfied, the electric field may be different.

• Infrared radiation is a part of the electromagnetic spectrum. Infrared radiations are also known as thermal or heat waves.
• The range of wavelength is between 710nm to 1mm.
• These consist of heat inducing property. These rays have applications in the area of heat production. these rays keep earth hot.
• These are emitted by certain semiconductor light-emitting diodes.
• Water vapour traps heat radiated from Earth so as infra red rays.
• The thermal motion of the materials increases after they absorb infrared rays. 

So, Option (i) and (iv) is are not correct.
Hence the correct answer is Option-1-Both (i) and (iv). 

• The iron core of a transformer is made of Laminated silicon steel with special insulated coating to limit Eddy current loss.
• Electrical steel, also called lamination steel is specialty steel tailored to produce certain magnetic properties, such as a small hysteresis area (small energy dissipation per cycle, or low core loss) and high permeability.
  

• When a conductive material is subjected to a time-varying magnetic flux, eddy currents are generated in the conductor.
• These eddy currents circulate inside the conductor generating a magnetic field of opposite polarity as the applied magnetic field. The interaction of the two magnetic fields causes a force that resists the change in magnetic flux.
• However, due to the internal resistance of the conductive material, the eddy currents will be dissipated into heat and the force will die out. As the eddy currents are dissipated, energy is removed from the system, thus producing a damping effect.

Coefficient of mutual induction:-
It is a measure of the induction between two circuits, It is the ratio of the electromotive force in a circuit to the corresponding change of current in neighboring circuits; usually measured in henries.
Coefficient of mutual induction is the ratio of induced e.m.f in secondary coil to the rate of change of current in primary coil.

Given :
            ϕ = 12t²+7t+C
where, C is a constant, t is in sec, ϕ in milli-weber
The induced e.m.f. in the loop at t=5, on differentiating the equation with respect to 't'.
        We know that,  E = - dϕ / dt

So,  d​(12t²+7t+C) / dt
                =  24t+7
 at            t = 5
                 E ​= 24×(5)+7
                          = 120+7
                          = 127 mV

So, E = - dϕ / dt = - 127 mV

4. 0.1063 m

The force on a charge q moving at a velocity v in a magnetic field B is described by the equation:

• The force can be calculated using the formula: F = q(v × B).
• Here, F is the magnetic force, q is the charge, v is the velocity, and B is the magnetic field.
• The direction of the force is determined by the right-hand rule.

In this scenario, the answer is C.

As,
B=μ_onI/2a
a ->radius
B ∝1/a
B₁/B₂=a₂/a₁
B₁=2B₂
B₂=(1/2) x B₁,
Magnetic field is halved.

From Biot-Savart law, magnetic field at a point p, B= (μ0​/4π)∫ [(Idl×r​)/ r3]
where r is the distance of point p from conductor and I is the current in the conductor.
Thus magnetic field due to current carrying conductor depends on the current flowing through conductor and distance from the conductor and length of the conductor.
 

Solution : 

The correct option is Option A.

Laws of refraction;-

The incident ray,the refracted ray and the normal to the refracting surface at the point of incidence lie in the same plane.

For a given pair of media and for a given colour of light the ration between the sine of angle of incidence to the sine of refraction is a constant.This constant is known as refractive index of the second medium with respect to the first medium.

When a ray of light passes through a glass slab, ∠i,∠r and the normal all lie in the same plane.

When a ray of light passes from one medium to another, here from air to glass or glass to air, the ratio sini / sinr = constant.

When the lens is in air, we have (from lens maker's equation), 1/20 = [(1.5/1) - 1) (1/R1- 1/R2). 
We are not bothered about the signs of R1 and R2 since they are unknown quantities. 
Even though we know that the convergent lens will become divergent in the denser medium, we write the lens maker's equation without bothering about the sign of its unknown focal length in the liquid. If if is the focal length in the liquid, we can write, 
1/f = ((1.5/1.6) - 1) (1/R1 - 1/R2). 
Dividing the first equation by the second, we obtain f/20 = 0.5x1.6/(-0.1) from which f = -160 cm

In the photoelectric effect, the work function is the minimum amount of energy (per photon) needed to eject an electron from the surface of a metal.Electrons ejected from a sodium metal surface were measured as an electric current.The minimum energy required to eject an electron from the surface is called the photoelectric work function.
This energy (work function) is a measure of how firmly a particular metal holds its electrons. The work function is important in applications involving electron emission from metals, as in photoelectric devices and cathode-ray tubes.

The correct answer would be option B. Applying a very strong magnetic field.
Applying a very strong magnetic field to a metal we don’t know the electron emission.

Φ= hνλ => 2eV= 6.626 x 10^-34 x ν

2 x 1.6 x 10^-19= 6.626 x 10^-34 x ν

On solving we get ν = 4.6 x 10¹⁴ Hz.

The plum pudding model is one of several scientific models of the atom. According to J.J. Thomson atomic models the positive particles in the atom form something like the "batter" in a plum pudding, while the negative electrons are scattered through this "batter".

A spectrum is an assembly of energy levels in the form of radiations emitted by an atom in its excited state. Every atom gives discontinuous line spectra. Each line in the spectra corresponds to a specific wavelength and it is unique to a given element so no two elements give the same pattern of lines in their spectra.

Using formula for Paschen series,
1/λ=R[(1/3²)-1/n₂²],n₂=4,5,6….
For shortest wavelength, n₂=∞
∴1/λ=R[(1/3²)-1/∞²],n₂=R/9 or λ=9/R ≈ 820.4 nm

The nuclide (nucleus) consists of neutrons and protons (when combined called nucleons).
Thus,
No. of protons in 92U²³⁸ = 92,
No. of neutrons = 146 (238 – 92)
No. of nucleons = 238 (146 + 92)

Most nuclei are approximately spherical. The average radius of a nucleus with A nucleons is R = R₀A^1/3, where R⁰ = 1.2*10^-15 m. The volume of the nucleus is directly proportional to the total number of nucleons. This suggests that all nuclei have nearly the same density.

Knee voltage- it is that forward voltage beyond which current start increasing rapidly, but below knee voltage variation of forward current and applied voltage is linear.
The electric field in a region is given by, E=V/l.
where V is the potential and l is the length or distance of the region in which it has to be measured.
now, E=V/l
E=0.8/2×10^-6 m
E= 0.4 MV/m
 

A rectifier is a device which converts a.c (alternating current) to d.c( direct current), which flows in only one direction. This process is known as Rectification.
This is done using a p-n junction diode. 
A p-n junction diode allows electric current in only forward bias condition and blocks electric current in reverse bias conditions.
 In other words, a diode allows electric current in one direction. This unique property of diode allows it to act like a Rectifier.
 

In a half wave rectifier, the secondary coil S of the transformer is connected to​ both junction diode and a load resistance.

In full wave rectification the input frequency is doubled. Because all the negative components in the AC input signal are converted into positive components. Hence, the positive components are doubled.
Therefore in full wave rectification output frequency will be 100 Hz i.e. double that of input frequency 50 Hz.
 

Photoconductivity, as a well-known optical and electrical phenomenon in semiconductor, is an effect that the electrical conductivity increases due to the absorption of light radiation.

When the resistors are connected in series, and current is passed through them, the current passing through each of the resistor is the same. This is because, the resistors are connected end to end and, therefore, there is only one path for the current to flow through.

When three resistors are connected in series, then the equivalent resistance of this combination is R_s = R₁ + R₂ + R₃. So, if 3 resistors having resistances 10, 15, and 20 ohms, are connected in series, then equivalent resistance of this combination is R_s = 10 + 15 + 20 = 45 ohms.

The equation → ∑e = ∑IR is applicable to Kirchhoff’s second law. This law is also known as Kirchhoff’s loop rule. This expression tells us that in a closed loop, the algebraic sum of the emfs is equal to the algebraic sum of the products of the resistance and currents flowing through them.