Physics: CUET Mock Test - 6 - CUET MCQ

Each of the message signals has different ranges of frequencies. The type of communication system needed for a given signal depends on the bad of frequencies which are considered essential for the communication process.

The frequencies for transmitting music is which of the following?
a) Low
b) High
c) Moderate
d) Very high

When the bandwidth is large enough to accommodate a few harmonics, the information is not lost and the rectangular signal is more or less recovered. This is so because the higher the harmonic, the less is its contribution to the waveform. Therefore, the value of the harmonic is inversely proportional to its contribution to the waveform.

For speech signals, the frequency range of 300 Hz to 3100 Hz is considered adequate. Therefore, speech signals require a bandwidth of 2800 Hz (3100 Hz – 300 Hz) for commercial telephonic communication.

SiO₂ acts as a diffusion mask permitting selective diffusions into the silicon wafer through the window etched into oxide. In other words, it is used for creating a protective SiO₂ layer on the wafer surface of the IC. Therefore, SiO₂ acts as an insulating component for integrated circuits.

An Integrated circuit (IC) is an assembly of electronic components, fabricated as a single unit, in which miniaturized active devices and passive devices and their interconnections are built upon a thin substrate of semiconductor material. There are about 600 different types of Integrated circuits.

Silicon is the one mainly used in the production of Integrated circuits. This is because silicon possesses many characteristics that are ideal for ICs. Silicon is used because it can be used as either an insulator or a semiconductor. This property is crucial for the manufacture of Integrated Circuits.

The maximum power rating possible for a microcircuit is 10 Watts. Integrated Circuits can’t be repaired because the individual components inside the IC are too small. As a result, the facility rating for many of the IC’s doesn’t exceed quite 10 watts. It’s impossible to manufacture high power IC’s and this is often one among the most important disadvantages of Integrated Circuits.

ICs are both small in size as well as in weight. As the fabrication process is used for the integration of active and passive components on a silicon integrated circuit, the IC becomes a lot smaller. Also, due to its small size, the weight of the IC reduces, when compared to a discrete circuit.

Capacitors are not easy to fabricate on an Integrated Circuit. In fact, they are the most difficult ones to fabricate. This is because capacitors require a lot of attributes such as electromagnetic compatibility, microfabrication techniques, new magnetic materials, etc. and to integrate them, it costs a lot. Therefore, fabricating capacitors is a challenging task.

A transistor has three doped regions forming two p-n junctions between them. There are two types of transistors, namely n-p-n transistors and p-n-p transistors. In n-p-n transistors, the two segments of the n-type semiconductor are separated by a segment of p-type semiconductor, and in a p-n-p transistor, it’s just the opposite scenario.

The collector is the section on the other side of the transistor that collects the charge carriers supplied by the emitter. It is moderately doped but large in size and is always kept in reverse bias with respect to the base.

In an n-p-n transistor, as the base is very thin and lightly doped, a very few electrons from the emitter combine with the holes of the base, giving rise to base current and the electrons finally collected by the positive terminal of the battery gives rise to collector current. This base current is a small fraction of collector current depending on the shape of a transistor, thickness of the base, doping levels, and bias voltage.

The expression for current gain is given as:
β = I₀ / I_B
I_C = 50I_B
Since, I_E = I_B+I_C 
⇒ I_E = I_B + 50I_B
I_E = 51I_B
I_B = IE51 = 5.551 = 0.107 mA

The expression of voltage gain is as follows:
A_V = αR_L / R_e
Given: α = 0.90, R_L = 5.0 kΩ = 5000 Ω, R_e = 50 Ω
A_V = 0.90 × 5000 / 50
A_V = 90

Power gain is defined as the ratio of output power to input power. It can also be determined as the product of current gain and voltage gain.
Given: α = 0.80, voltage gain (A_V) = 95
The required equation
⇒ A_P = α × A_V
A_P = 0.80×95
A_P = 76

I_E = I_B + I_C
I_E / I_C = I_B / I_C + 1
1α = 1 / β + 1
α = β / 1 + β
Therefore, β = α / 1−α

Emitter is the section or region on one side of the transistor that supplies charge carriers. It is heavily doped and is always kept forward biased with respect to the base so that it can supply a large number of charge carriers to the base.

The radius of an electron orbit in a hydrogen atom is of the order of 10^-11 m. It is equal to the most probable distance between the nucleus and the electron in a hydrogen atom in its ground state.

Increase in angular momentum = h /2π.
h /2π = 6.6 × 10⁻³⁴ /2 × 3.14
h /2π = 1.05 × 10^-34 Js.

For the first excited level, n = 2.
r₂ = (2)²r₀ = 4r₀.
So, when a hydrogen atom is in its first excited level, its radius is 4 times of the Bohr radius.

n = 4.
The number of spectral lines emitted = .
(4*3)/2
= 6

Bohr model of atoms assumes that the angular momentum of electrons is quantized. The atom is held between the nucleus and surroundings by electrostatic forces. The other options are not valid.

λ = 6557 × 10^-10 m.

The equation is given as:

From this, we can understand that r_n is directly proportional to n².

Davisson and Germer experiment proves the concept of wave nature of matter particles. The Davisson–Germer experiment provides a critically important confirmation of the de-Broglie hypothesis, which said that particles, such as electrons, are of dual nature.

The crystal used in the Davisson – Germer experiment is nickel. A fine beam of electrons is made to fall on the surface of the nickel crystal. As a result, the electrons are scattered in all directions by the atoms of the crystal.

Bragg’s law is a special case of Laue diffraction, it gives the angles for coherent and incoherent scattering from a crystal lattice. The expression for Bragg’s law is given as:
2d sin⁡θ=nλ

Davisson – Germer experiment uses an electron gun to produce a fine beam of electrons which can be accelerated to any desired velocity by applying a suitable voltage across the gun. The others mentioned do not find an application here.

From Einstein’s photoelectric equation, we have
12 mv² = h(v – v₀).
Since the frequency of blue light is greater than that of the red light, blue light emits electrons of greater kinetic energy.