IIITH-UGEE SERIES

Physics

Kinetic Theory

16 previous year questions.

Volume: 16 Ques

Yield: Medium

High-Yield Trend

14

2025

2

2024

Chapter Questions
16 MCQs

01

PYQ 2024

medium

physics ID: iiith-ug

Helium is two times heavier than H2. The average kinetic energy per molecule for helium at 300K is

1

twice as H2

2

same as H2

3

half as H2

4

one fourth of H2

02

PYQ 2024

easy

physics ID: iiith-ug

Consider a rope fixed at both ends under tension so that it is horizontal (i.e. assume the rope is along x-axis, with gravity acting along z-axis). Now the right end is continually oscillated at high frequency n (say n=100 Hz) horizontally and in a direction along the rope; amplitude of oscillation is negligible. The oscillation travells along the rope and is reflected at the left end. Let the total length of rope be l, total mass be m and the acceleration due to gravity be g. After initial phase (say a mintue or so), the rope has __(BLANK-1)__ wave, which is __(BLANK-2)__ in nature. It results from superposition of left travelling and right travelling __(BLANK-3)__ waves. This resulting wave has a frequency __ (BLANK-4)_ that of oscillation frequency nu. Simple dimensional analysis indicates that the frequency of can be of the form: ___(BLANK-5)__ .

1

BLANK-1: travelling, oscillating, stationary, regular

2

BLANK-2: transverse, longitudinal, regular, irregular

3

BLANK-3: transverse, longitudinal, regular, irregular

4

BLANK-4: equal to, half, double, independent from

Official Solution

Correct Option: (1)

03

PYQ 2025

medium

physics ID: iiith-ug

For an air cooler to work at maximum efficiency:

1

Placed away from window & water has salt

2

Placed away from window & no salt in water

3

Placed towards window & water has salt

4

Placed towards window & no salt in water

04

PYQ 2025

medium

physics ID: iiith-ug

Water takes 10 minutes to boil on Earth. If the boiling point of water is lower on Mars, it would take textunderscoretextunderscoretextunderscoretextunderscoretextunderscoretextunderscore than 10 minutes.

1

Less

2

Same

3

More

4

Cannot boil properly

05

PYQ 2025

medium

physics ID: iiith-ug

If you shrink to one billionth of your size, how would the world appear?

1

Radiant and shiny

2

Jagged landscape

3

Wet

4

Frozen lake

06

PYQ 2025

medium

physics ID: iiith-ug

In summer, an air cooler is used in a room. To achieve maximum cooling efficiency, which of the following setups is best?

1

Cooler fan facing the window, no salt in water

2

Cooler fan facing away from window, no salt

3

Cooler fan facing window, salt added to water

4

Cooler fan facing away from window, salt added

07

PYQ 2025

medium

physics ID: iiith-ug

Aryan and Mira are playing with soap bubbles in sunlight. Aryan notices that the bubble appears purple, which is unusual. A scientist explains the phenomenon and gives the following statements: I. The colour is due to interference of light in a thin film. II. As the bubble thickness increases, the reflected colour shifts towards higher wavelength. III. Purple colour appears because shorter wavelengths undergo constructive interference first. IV. The colour is due to absorption of light by soap. Which of the above statements correctly explain the observation?

1

I and II only

2

I, II and III only

3

II and IV only

4

I and IV only

Official Solution

Correct Option: (1)

08

PYQ 2025

medium

physics ID: iiith-ug

To increase cooling efficiency of an air cooler, which setup is best?

1

Fan towards open window, no salt in water

2

Fan away from window, no salt

3

Fan towards window, salt added

4

Fan away from window, salt added

09

PYQ 2025

medium

physics ID: iiith-ug

As the thickness of a soap bubble increases under sunlight, which colour appears later?

1

Violet

2

Blue

3

Green

4

Red

10

PYQ 2025

medium

physics ID: iiith-ug

Rice takes about 10 minutes to boil on Earth in open conditions. If the same experiment is performed on Mars, what will happen?

1

Rice will boil in the same time

2

Rice will boil faster

3

Rice will take more time to boil

4

Rice will not boil properly

11

PYQ 2025

medium

physics ID: iiith-ug

When an air cooler is used in a closed room, air is pulled through the cooler pads. Which thermodynamic process does the air approximately undergo?

1

Isothermal

2

Adiabatic

3

Isochoric

4

Isoenthalpic

5

Isentropic

Official Solution

Correct Option: (4)

12

PYQ 2025

medium

physics ID: iiith-ug

An air cooler will work most efficiently under which condition?

1

Cooler facing window, no salt in water

2

Cooler facing away from window, no salt

3

Cooler facing window, salt added in water

4

Cooler facing away from window, salt added

13

PYQ 2025

medium

physics ID: iiith-ug

Air blown out by an air cooler in a closed room approximately undergoes which process?

1

Isothermal

2

Adiabatic

3

Isoenthalpic

4

Isobaric

5

None

14

PYQ 2025

medium

physics ID: iiith-ug

In summer, when an air cooler is used, the room temperature decreases. What is the primary thermodynamic process responsible for cooling?

1

Conduction

2

Convection

3

Evaporation

4

Radiation

15

PYQ 2025

medium

physics ID: iiith-ug

For maximum cooling efficiency, an air cooler should be placed:

1

Facing the window

2

Away from the window

3

In the center of the room

4

Near the ceiling

16

PYQ 2025

medium

physics ID: iiith-ug

Two children observe soap bubbles in sunlight. Initially the bubble appears bluish, but after some time it turns yellowish. Which of the following statements are correct? I. The colour shifts towards higher wavelength. II. Blue/violet colours disappear earlier than red. III. For sufficiently thick bubbles, the bubble appears white.

1

I and II only

2

II and III only

3

I and III only

4

I, II and III

Official Solution

Correct Option: (4)

Step 1: Understanding the Question: The question describes the changing colors of a soap bubble and asks which of the given statements about the phenomenon are correct. The color change is due to thin-film interference. Step 2: Detailed Explanation: Analysis of Statement I: The colour shifts towards higher wavelength. The initial color is bluish (shorter wavelength) and it turns yellowish (longer wavelength). The visible spectrum in order of increasing wavelength is Violet-Indigo-Blue-Green-Yellow-Orange-Red (VIBGYOR). A shift from blue to yellow is indeed a shift towards a higher wavelength. Thus, statement I is correct. Analysis of Statement II: Blue/violet colours disappear earlier than red. The color seen is due to constructive interference, for which the condition (for near-normal incidence) is (2nt = (m + 1/2)lambda), where (n) is the refractive index, (t) is the film thickness, and (lambda) is the wavelength. Over time, a soap bubble thins due to gravity and evaporation, so its thickness (t) decreases. As (t) becomes very small, it can no longer satisfy the constructive interference condition for any visible wavelength. Since blue/violet light has the shortest wavelength, it requires the smallest thickness to interfere constructively. As the film thins further, it becomes too thin even for blue light, causing it to "disappear" first, before the longer wavelengths like red. Thus, statement II is correct. Analysis of Statement III: For sufficiently thick bubbles, the bubble appears white. When the bubble film is very thick compared to the wavelengths of visible light (e.g., many micrometers), constructive and destructive interference occur for many different wavelengths across the visible spectrum at the same location. The reflected light is a mix of all these colors, and the combination of all colors of the spectrum appears as white light to the human eye. Thus, statement III is correct. Step 3: Final Answer: All three statements accurately describe phenomena related to thin-film interference in soap bubbles. Therefore, all three statements are correct.