Physics Test 205

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Physics Test 205

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Weekly Quiz Competition

Question 1
4 / -1

In an oscillating spring mass system, a spring is connected to a box filled with the sand. As the box oscillates, sand leaks slowly out of the box vertically so that the average frequency ω (t) and average amplitude A (t) of the system changes with time t. Which of the following options systemically depicts these changes correctly?

A

B

C

D

Solution

At any point of time, time period is given by

T = 2π √(m / k)

Here m is decreasing, so time period T will be decreasing

Since ω = 2π / T

Hence as mass leaks, ω will increase

Now, at any instant

mg = kx₀

So, equilibrium length x₀ = mg / k, where m is decreasing

So, equilibrium length will decrease.

So, amplitude also go on decreasing.
Question 2
4 / -1

At absolute zero temperature may be defined as that temperature at which

A
Volume is maximum

B
Root mean square velocity of the gas molecule reduces to zero

C
Temperature is 273 K

D
Mass of molecules of gas is zero

Solution

At 0K temperature we know that there is no molecular motion, that is the KE of the particles gets 0. Thus we can say the combined KE of a gaseous system is zero, but as there combined mass cant be zero thus the combined of the square of velocities of the particles is zero, which means that the root mean square velocity of the gas is zero.
Question 3
4 / -1

The restoring force in a simple harmonic motion is _________ in magnitude when the particle is instantaneously at rest.

A
zero

B
maximum

C
minimum

D
none of these

Solution

The restoring force in a simple harmonic motion is maximum in magnitude when the particle is instantaneously at rest because in SHM object’s tendency is to return to mean position and here particle is instantaneously at rest after that instant restoring force will be max to bring particle to mean position.
Question 4
4 / -1

In an interference experiment monochromatic light is replaced by white light, we will see:

A
uniform darkness on the screen

B
a few coloured bands and then uniform illumination

C
equally spaced white and dark bands

D
uniform illumination on the screen

Solution

white light is made up of seven colors VIBGYOR. All the seven colors will show interference, we can treat each color separately as a monochromatic light and study their interference separately. Each light will have their bright and dark fringes separately but at y=0 i.e for a center, each lights bright fringe will coincide. Two or more lights may have their bright and dark Fringe together or bright for one and dark for others may coincide depending upon the situation.
Question 5
4 / -1

A photodiode is used preferably in

A
to increase voltage

B
in forward bias condition

C
to convert electrical energy into light

D
in reverse bias condition

Solution

Photo diode is used to detect light.

In a reverse biased condition, the width of the depletion region increases as the applied reverse bias voltage increases across the diode. So, by applying a larger voltage, more of the incident photons are converted to electric current thereby increasing the efficiency.

In forward biased conditions, the width of the depletion region decreases so only a small portion of the incident photons get converted to electric current and hence the efficiency is less.

Hence photo diode in reverse biased condition detects light.
Question 6
4 / -1

Which one of the following statements is false?

A
Pure Si doped with trivalent impurities gives a p-type semiconductor.

B
The majority carriers in an n-type semiconductor are holes.

C
Minority carriers in a p-type semiconductor are electrons.

D
The resistance of intrinsic semiconductors decreases with an increase in temperature.

Solution
Question 7
4 / -1

Which one of the following phenomena is notexplained by Huygen’s construction ofwavefront?

A
Refraction

B
Reflection

C
Diffraction

D
Origin of spectra

Solution

Huygen's construction of wavefront does not apply to origin of spectra which is explained by quantum theory
Question 8
4 / -1

The truth table given below is for a gate with A and B as inputs and C as output. Which of the gates will obey this truth table?

A
OR

B
XOR

C
AND

D
NAND

Solution

We can observe from the table that Yˉ=A.B⇒Y=AB

So, the table represents a NAND gate.
Question 9
4 / -1

A light ray falls on a rectangular glass slab as shown. The index of refraction of the glass, if total internal reflection is to occur at the vertical face, is

A

B

C

D

Solution
Question 10
4 / -1

Just before setting, the sun may appear to be elliptical. This happens due to:

A
Refraction

B
Dispersion

C
Reflection

D
Diffraction

Solution

Refraction of light ray through the atmosphere may cause different magnification in mutually perpendicular directions.

Sunlight enters the Earth's atmosphere from the vacuum of space. The refractive index of air with respect to vacuum is 1.0029. This means that the speed of light in air is 1.0029 times slower than the speed of light in vacuum. This causes the light rays to bend towards the normal (refraction).