UPSC CDS-1

31. The area under the velocity-time graph for a particle moving in a stra

The area under the velocity-time graph for a particle moving in a straight line with uniform acceleration gives

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its average velocity
its net displacement
the distance travelled by it
its average speed
This question was previously asked in
UPSC CDS-1 – 2023
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For a particle moving in a straight line, the area under the velocity-time graph represents the displacement of the particle during the given time interval. If the velocity is plotted on the y-axis and time on the x-axis, the area under the curve between two time points gives the change in position (displacement) over that period. This is valid even if the velocity is non-uniform or changes direction.
The area under the velocity-time graph represents the net displacement.
If the particle moves in only one direction (velocity does not change sign), the magnitude of the displacement is equal to the distance traveled. However, if the velocity-time graph goes below the time axis (indicating motion in the opposite direction), the area below the axis is considered negative displacement. The net displacement is the sum of the signed areas. The total distance traveled would be the sum of the magnitudes of the areas. The question specifies uniform acceleration, which means the graph is a straight line, but it doesn’t preclude the velocity from changing direction (e.g., starting with negative velocity and accelerating in the positive direction).

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32. A 100 W electric bulb is used for 10 hours a day. How many units of el

A 100 W electric bulb is used for 10 hours a day. How many units of electrical energy are consumed by the bulb in 3 days? (1 unit = 1 kWh)

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3.00
1.08
2.16
0.33
This question was previously asked in
UPSC CDS-1 – 2023
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The energy consumed by an electrical appliance is calculated by multiplying its power rating by the time it is used.
Power (P) = 100 W.
Time used per day = 10 hours.
Total time used in 3 days = 10 hours/day × 3 days = 30 hours.
Energy consumed (in Watt-hours) = P × Time = 100 W × 30 hours = 3000 Wh.
To convert Watt-hours to kilowatt-hours (units), divide by 1000:
Energy consumed (in kWh) = 3000 Wh / 1000 Wh/kWh = 3 kWh.
Since 1 unit = 1 kWh, the energy consumed is 3 units.
Electrical energy consumed is calculated as Power × Time. Energy unit (kWh) = Power (kW) × Time (h).
Electricity meters in homes measure energy consumption in kilowatt-hours (kWh), which are commonly referred to as ‘units’. The cost of electricity is usually charged per unit consumed.

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33. Consider the following statements about the microphone and the speaker

Consider the following statements about the microphone and the speaker of a mobile phone :

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  • 1. The microphone converts sound to a mechanical signal.
  • 2. The microphone converts sound to an electrical signal.
  • 3. The speaker converts a mechanical signal to sound.
  • 4. The speaker converts an electrical signal to sound.

Which of the statements given above are correct?

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1 and 3
1 and 4
2 and 3
2 and 4
This question was previously asked in
UPSC CDS-1 – 2023
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A microphone is a transducer that converts sound waves (acoustic energy) into electrical signals. This electrical signal is then processed. A speaker is also a transducer that converts an electrical signal back into sound waves (acoustic energy). Therefore, statement 2 (microphone converts sound to an electrical signal) and statement 4 (speaker converts an electrical signal to sound) are correct. Statements 1 and 3 involving “mechanical signal” in this context are incorrect as the primary conversion involves energy forms like sound and electricity, mediated by mechanical *vibrations* but the output/input are electrical/sound signals.
Microphones convert sound energy into electrical energy. Speakers convert electrical energy into sound energy.
Microphones typically work by diaphragm vibration caused by sound waves, which then generates an electrical signal (e.g., carbon, dynamic, condenser microphones). Speakers work by an electrical current flowing through a coil in a magnetic field, causing the coil (and an attached diaphragm/cone) to vibrate, producing sound waves.

34. A person burned a firecracker in front of a cliff and heard its echo 5

A person burned a firecracker in front of a cliff and heard its echo 5 s after it burst. The distance of the cliff from the person, if the speed of the sound is 340 m/s, is close to

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1700 m
170 m
85 m
850 m
This question was previously asked in
UPSC CDS-1 – 2023
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The time taken for the echo to be heard is the time it takes for the sound to travel from the person to the cliff and then back to the person. The total distance covered by the sound is therefore twice the distance between the person and the cliff. Given the speed of sound (v) is 340 m/s and the total time (t) for the echo is 5 s, the total distance (d_total) is v × t = 340 m/s × 5 s = 1700 m. The distance to the cliff (d_cliff) is half of the total distance: d_cliff = d_total / 2 = 1700 m / 2 = 850 m.
The total distance covered by an echo is twice the distance to the reflecting surface. Distance = Speed × Time.
Echo is the reflection of sound waves from a surface. The time delay between the original sound and the echo is used to determine the distance of the reflecting surface. This principle is used in sonar and ultrasound imaging.

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35. The blood pressure of a normal human being is found to be 120/80 mmHg.

The blood pressure of a normal human being is found to be 120/80 mmHg. These ‘numbers’ represent the blood pressure at

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ventricular contraction and ventricular relaxation, respectively
ventricular relaxation and ventricular contraction, respectively
auricular contraction and auricular relaxation, respectively
ventricular contraction and auricular contraction, respectively
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UPSC CDS-1 – 2023
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The blood pressure reading 120/80 mmHg represents the systolic pressure (120 mmHg) over the diastolic pressure (80 mmHg). Systolic pressure is the peak pressure in the arteries during ventricular contraction (systole), while diastolic pressure is the lowest pressure in the arteries during ventricular relaxation (diastole). Therefore, 120 mmHg represents the pressure during ventricular contraction and 80 mmHg represents the pressure during ventricular relaxation.
Systolic pressure corresponds to ventricular contraction; diastolic pressure corresponds to ventricular relaxation.
Blood pressure is typically measured in the brachial artery of the arm. The measurement reflects the pressure exerted by the blood on the walls of the arteries. Normal blood pressure is considered to be around 120/80 mmHg, though this can vary slightly among individuals. High blood pressure (hypertension) is a significant risk factor for cardiovascular diseases.

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36. Which one of the following statements regarding bile secreted by liver

Which one of the following statements regarding bile secreted by liver is not correct?

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Bile contains enzymes for digestion of lipids.
Bile facilitates emulsification of fats.
Bile neutralizes the acidic pH of the food coming from stomach.
Bile makes the pH of the food alkaline and facilitates action of pancreatic enzymes.
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UPSC CDS-1 – 2023
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Bile is secreted by the liver and stored in the gallbladder. It plays a crucial role in digestion, particularly of fats, but it does not contain digestive enzymes itself. Statement A is incorrect because bile lacks the enzymes necessary for the chemical breakdown of lipids or any other macromolecules.
The functions of bile primarily include emulsification of fats and neutralization of acidic chyme.
Bile contains bile salts, bile pigments, cholesterol, and phospholipids. Bile salts act as emulsifying agents, breaking large fat globules into smaller droplets, increasing the surface area for enzymatic action by lipases (which are present in pancreatic juice). Bile is alkaline (pH ~7.5-8.8) and helps neutralize the acidic food entering the duodenum from the stomach, creating an optimal environment for the action of pancreatic enzymes.

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37. If the red blood cells (RBCs) of human blood are isolated and are dilu

If the red blood cells (RBCs) of human blood are isolated and are diluted in normal saline (an isotonic solution to blood), what will happen to the RBCs?

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The RBCs will swell
The RBCs will swell and burst
The RBCs will shrink
No change in the diameters of the RBCs
This question was previously asked in
UPSC CDS-1 – 2023
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If red blood cells are placed in normal saline, there will be no change in their diameters.
Normal saline (0.9% sodium chloride solution) is isotonic to the cytoplasm of human red blood cells. This means it has the same solute concentration and thus the same water potential as the inside of the RBCs.
In an isotonic solution, there is no net movement of water across the cell membrane via osmosis. Water molecules move in and out of the cell at equal rates, maintaining the cell’s shape and volume. If RBCs were placed in a hypotonic solution (lower solute concentration), water would enter the cells causing them to swell and possibly burst (hemolysis). If placed in a hypertonic solution (higher solute concentration), water would leave the cells causing them to shrink (crenation).

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38. A leaf was plucked from a plant on a sunny day and kept for 2 minutes

A leaf was plucked from a plant on a sunny day and kept for 2 minutes in boiling water. It was subsequently immersed in boiling alcohol and treated with iodine solution. What will be the final colour of the leaf after the test?

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Colourless
Green
Blue
White
This question was previously asked in
UPSC CDS-1 – 2023
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After treating the leaf with iodine solution following de-colourisation, the final colour will be blue (specifically blue-black).
This experiment is a standard test for the presence of starch in a leaf, which is a product of photosynthesis. Keeping the leaf on a sunny day ensures starch production. Boiling water kills the cells. Boiling alcohol removes the chlorophyll, making the leaf pale so the colour change with iodine is visible. Iodine solution turns blue-black in the presence of starch.
The steps are designed to isolate the starch and make its detection by iodine possible. Removing chlorophyll is crucial because it would mask the colour change. A leaf from a plant kept in darkness for a day or two would show no starch and would remain brown/yellow with iodine.

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39. A sprinter feels cramps and pain in the thigh muscles after a run. Thi

A sprinter feels cramps and pain in the thigh muscles after a run. This is due to accumulation of

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lactic acid
CO₂
pyruvic acid
ethanol
This question was previously asked in
UPSC CDS-1 – 2023
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Muscle cramps and pain after intense exercise like sprinting are primarily caused by the accumulation of lactic acid.
During strenuous exercise when oxygen supply to muscle cells is limited, muscles switch to anaerobic respiration. This process breaks down glucose to produce energy (ATP) and lactic acid as a byproduct. The buildup of lactic acid lowers the pH in muscle cells, contributing to fatigue, pain, and muscle cramps.
Under sufficient oxygen conditions, muscles perform aerobic respiration, breaking down glucose completely to produce much more ATP, carbon dioxide, and water. Pyruvic acid is an intermediate product in both aerobic and anaerobic respiration. Ethanol is produced during anaerobic respiration in yeast and some plant tissues, but not typically in human muscles.

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40. Recently, archaeological studies at which one among the following reve

Recently, archaeological studies at which one among the following revealed that by 1200 BCE there was a flourishing agrarian civilization and the cultivation of rice was well-established at this place ?

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Raichur Doab
Krishna Delta
Vicinity of Vamsadhara river
Vicinity of Thamirabarani river
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UPSC CDS-1 – 2022
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Recent archaeological excavations near the Thamirabarani river in Tamil Nadu have provided evidence of a flourishing agrarian civilization and established rice cultivation dating back to around 1200 BCE.
Excavations at sites like Sivakalai, located in the vicinity of the Thamirabarani river, have yielded datable materials, including rice grains in burial urns, which have been dated to about 3200 years ago (circa 1200 BCE). This finding pushes back the timeline of established Iron Age culture and paddy cultivation in Tamil Nadu.
Archaeological investigations along the Thamirabarani river valley are part of broader efforts to understand the ancient history and culture of Tamil Nadu, including the origins of its script and civilization. Other important sites like Adichanallur are also located in this region.

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