Physics: CUET Mock Test - 9 - CUET MCQ

A wire bound resistor is an electrical passive component that limits current. Wire-bound resistors are made by winding the wires of an alloy like manganin on an insulating base. They are relatively insensitive to temperature.

The correct option for the phase difference (Δϕ) between two superimposing waves to obtain constructive interference and hence a bright band is:
Δϕ = np; n = 1, 2, 3, 4, 5

• For constructive interference to occur, the waves must be in phase, i.e., their crests and troughs must coincide.
• If two waves of the same frequency and amplitude meet at a point with a path difference of integer multiple of wavelength (nλ), then they will be in phase and add up constructively to produce a bright band.
• The phase difference between the two waves in this case is Δϕ = 2π(nλ/λ) = 2πn, where n is an integer.
• Since 2πn is equivalent to np, where p is the wavelength, the correct option is Δϕ = np; n = 1, 2, 3, 4, 5.

The correct answer is option "1"

When two sources of intensities Io interfere, the resultant intensity depends on the phase difference ϕ between the two sources.

For all other values of ϕ, the resultant intensity is given by:
I = 4Io cos²(ϕ/2)

Since the phase difference ϕ is randomly varying, we need to take the average of the above equation over all possible values of ϕ. The average value of cos²(ϕ/2) over all possible values of ϕ is 1/2.

Therefore, the average value of I is:
I = 4Io × 1/2 = 2Io
we will observe an average intensity that will be given by I = 2 Io at all points.
So, the resultant intensity at the centre of the screen is 2Io
The correct answer is option "3"

• In Young's double-slit experiment, when both slits are open, light passing through the two slits creates an interference pattern on the screen with bright and dark fringes. However, when one of the slits is closed, the interference pattern disappears, and only a diffraction pattern is obtained on the screen.
• The diffraction pattern obtained when one of the slits is closed is due to the bending of light as it passes through the open slit.
• The light spreads out, creating a wider central maximum and a series of secondary maxima and minima on either side. The intensity of the central maximum decreases because the light from only one slit is contributing to it, while the intensity of the secondary maxima and minima increases because the light from one slit is focused into a narrower region.
• If one of the slits is closed in Young's double-slit experiment, the interference pattern disappears, and only a diffraction pattern is obtained on the screen.
• The width of the central maximum increases, and the intensity of the central maximum decreases while the intensity of the secondary maxima and minima increases.
  ​The correct answer is option "3"

Concept:
In Young's double slit experiment, the fringe width (w) is given by the equation:
w = λD/d
where λ is the wavelength of light,
D is the distance between the slits and the screen, and
d is the distance between the two slits.

Explanation:
If the separation between the slits is halved, then d is also halved. Therefore, the new value of d will be d/2.
If the distance between the slits and the screen is doubled, then the new value of D will be 2D.
Substituting these values in the above equation, we get:
w' = λ(2D)/(d/2) = 4λD/d
Therefore, the new fringe width (w') will be four times i.e., it gets quadrupled the original fringe width (w).
The correct answer is option (4)

Concept:
In Young's double slit experiment, the fringe width (wavelength of light λ divided by the distance between the two slits d) is given by the formula:
w = λd/D
where D is the distance between the slits and the screen.
When the whole apparatus is immersed in water of refractive index n, the wavelength of light effectively decreases by a factor of n.
This is because the speed of light in water is slower than in air, and the frequency of light remains constant. Therefore, the new fringe width w' can be calculated as:
w' = λd/nD
where λ/n is the new wavelength of light in water.
Since the refractive index of water is 4/3, the new wavelength of light in water is (3/4)λ.
Substituting this into the equation above, we get:
w' =
= (3/4)w
where w is the original fringe width in the air.
Therefore, the new fringe width in water is (3/4) times the original fringe width in air.
Substituting the given value of the original fringe width w = 0.4 mm, we get:
w' = (3/4) × 0.4 mm = 0.3 mm
Therefore, the new fringe width when the whole apparatus is immersed in water of refractive index 4/3 is 0.3 mm.
The correct answer is option (3)

CONCEPT:

• Electromagnetic Spectrum is the orderly distribution of electromagnetic waves in accordance with their wavelength(λ) or frequency(ν) into a group of waves having widely differing properties. There are no sharply defined boundaries and these different waves do overlap each other.
• The table below represents the frequency range and application of various electromagnetic waves

EXPLANATION:

• The spectrum represents the arrangement in the order of frequency and wavelength.
• The decreasing order of wavelengths is opposite to the increase in frequency.
• The wavelength and frequency of waves are inversely related.

-------(1)

Then the waves can be arranged as

According to relationship 1, Equation 2 can be rewritten as

• Hence Option 2 is the answer

CONCEPT:

The De Broglie wavelength of the electron is written as;

°A

here, is the wavelength in °A and V in Volt is the potential difference.

CALCULATION:

Given,

The wavelength of the electron is 1.227 × 10−2 nm

1.227 × 10−2 nm = 1.227 × 10−11 m

1.227 × 10−11 m = 1.227 × 10−11 × 1010 °A

1.227 × 10−2 nm = 12.27 × 10−2 °A

Using equation (1) we have;

°A

⇒

⇒ ​

⇒ V = 10⁴ volts

Hence, option 2) is the correct answer.

The correct answer is rate of change in magnetic flux.Key Points

• Induced EMF in a coil during the phenomenon of electromagnetic induction is directly proportional to the rate of change in magnetic flux.
• Electromagnetic induction is the process of generating an electromotive force (EMF) in a conductor by changing the magnetic field around it.
• The magnitude of the induced EMF depends on the rate of change of magnetic flux through the coil.
• This means that the faster the magnetic field changes, the greater the induced EMF will be.

Additional Information

• Magnetic flux is the amount of magnetic field passing through a surface.
  • It is given by the product of the magnetic field strength and the area of the surface perpendicular to the field.
  • However, the induced EMF is directly proportional to the rate of change of magnetic flux, not the magnetic flux itself.
• Resistance of the circuit does not affect the magnitude of induced EMF.
  • It only affects the current flowing through the circuit according to Ohm's Law.
• The phenomenon of electromagnetic induction was discovered by Michael Faraday in 1831.
• Faraday's Law of Electromagnetic Induction states that the EMF induced in a circuit is proportional to the rate of change of magnetic flux through it.
• The direction of induced EMF is given by Lenz's Law, which states that the direction of the induced EMF is such that it opposes the change in magnetic flux that produced it.

Zener Diode is mostly used as Voltage Regulator.

CONCEPT:

Zener diode: A Semiconductor Diode blocks current in the reverse direction, but will suffer from premature breakdown or damage if the reverse voltage applied across becomes too high.

Zener diode as voltage regulator: The Zener diode is connected with its cathode terminal connected to the positive rail of the DC supply so it is reverse biased and will be operating in its breakdown condition. Resistor Rs is selected so to limit the maximum current flowing in the circuit.

EXPLANATION:

• A Zener diode is used as a voltage regulator in reverse biased mode.
• The breakdown voltage in the Zener diode when connected in the reverse-biased is called Zener voltage. This Zener voltage so steady and constant, it has huge applications in circuits, most importantly, voltage regulation.

So option 4 is correct.

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.

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.

A Van de Graff generators produces large voltage and less current. A Van de Graff generator is an electrostatic generator which creates very high electric potentials. It produces very high voltage direct current electricity at low current levels.

In Amplitude modulation, the modulating wave is superimposed on a high-frequency carrier wave such that the amplitude of the modulated wave varies as the amplitude of the modulating wave.

Amplitude modulation (AM) is used for broadcasting because it avoids receiver complexity. Moreover, only a diode and a capacitor are sufficient to separate the audio signal from the amplitude-modulated wave.

The modulation index for an AM wave is defined as the ratio of change in the amplitude of the carrier wave to the amplitude of the original carrier wave.

The communication channel for the transmission of a message signal that has a bandwidth of 200kHz is FM radio. AM radio is the channel required for a message signal having a bandwidth of 5 MHz. Other options are not valid.

In Amplitude modulation, the modulating wave is superimposed on a high-frequency carrier wave such that the amplitude of the modulated wave varies as the amplitude of the modulating wave. The frequency of the modulated wave is equal to the frequency of the carrier wave.

Noise is a form of amplitude variations in the transmitted signal due to several factors such as the atmosphere, industries, etc. This noise can be reduced by increasing the deviation of the frequency of the signal.

Pulse code modulation is the one preferred for digital communication. Pulse codes are used to convert an analog signal to a digital one. It is the standard form of digital audio in computers, compact discs, etc.

AGC stands for automatic gain control. Automatic gain control changes (AGC) the overall gain of a receiver automatically so that the strength of the received signal remains almost constant.

A rectifier is based on the fact that a forward bias p-n junction conducts and a reverse bias p-n junction does not conduct electricity. The rectifier is used to convert alternating current voltage (ac) to direct current voltage (dc).

For a half-wave rectifier,

r =1.21

The flow of electrons is termed electronic current. Electrons flow from the negative terminal to the positive.

Power P= V²/R​
If length reduced 10% then new resistance of filament will be R′.
R′=R−10% of R
R′=0.9R
Now new power of heater is P2​
P_2​= V²​​/R′ = V²/0.9R​​=1.1P
% increase power=11%

Potentiometer is a long wire of uniform cross section made of manganin.

• Both potentiometer and voltmeter are devices to measure potential difference.
• EMF is the terminal p.d between the electrodes of a cell in open circuit, i.e., when no current is drawn from it.
• 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.