UPSC CDS-2 Archives

41. A metal wire of length l and diameter d has a resistance R. What would

A metal wire of length l and diameter d has a resistance R. What would be the resistance of another wire of the same metal and of same length but having double the diameter ?

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R/4

R/2

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The resistance (R) of a wire is given by the formula R = ρ(L/A), where ρ is the resistivity of the material, L is the length, and A is the cross-sectional area. The area A of a circular wire is given by A = π(d/2)^2 = πd^2/4, where d is the diameter. So, R is inversely proportional to the square of the diameter (R ∝ 1/d^2).
If the diameter is doubled (2d), the new area becomes A’ = π(2d)^2/4 = π(4d^2)/4 = πd^2. This means the area becomes four times the original area (A’ = 4A).
Since R ∝ 1/A, the new resistance R’ will be R’ = R / (A’/A) = R / 4.

– Resistance is inversely proportional to the cross-sectional area of the wire.
– Cross-sectional area is proportional to the square of the diameter.

The resistivity (ρ) depends on the material of the wire, which is stated as the same in the question. The length (L) is also stated as the same. Therefore, only the change in diameter affects the resistance in this case.

42. The device used for measuring electric current in a circuit is called

The device used for measuring electric current in a circuit is called

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Ammeter

Motor

Voltmeter

Generator

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An ammeter is specifically designed and used to measure the flow of electric current (measured in Amperes) through a point in a circuit.

– An ammeter is connected in series within the circuit to measure the total current flowing through that part of the circuit.

A voltmeter is used to measure the potential difference (voltage) across two points in a circuit. A motor converts electrical energy into mechanical energy. A generator converts mechanical energy into electrical energy.

43. The pitch of a sound wave depends upon which one of its following char

The pitch of a sound wave depends upon which one of its following characteristics ?

Speed

Loudness

Amplitude

Frequency

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The pitch of a sound wave is determined by its frequency. Higher frequency corresponds to a higher pitch, and lower frequency corresponds to a lower pitch.

– Pitch is the quality of a sound governed by the rate of vibrations producing it; the degree of highness or lowness of a tone.
– Frequency is the number of vibrations per unit of time.

Loudness of a sound is related to its amplitude, not frequency. Speed is the rate at which the sound wave travels through a medium and is dependent on the medium’s properties.

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44. An electrical circuit having combinations of resistances and capacitan

An electrical circuit having combinations of resistances and capacitance is given below. The current, flowing through the circuit will be

1 A

2 A

1·5 A

0·5 A

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The circuit consists of a 10V DC voltage source, a 10 ohm resistor, a 20 ohm resistor, and a 10 µF capacitor. We are asked for the current flowing through the circuit. In a DC circuit with a capacitor, after the capacitor has been fully charged (steady state), no current flows through the branch containing the capacitor.

– The diagram shows the 10 ohm resistor in series with a parallel combination.
– The parallel combination consists of two branches: one with the 20 ohm resistor and the capacitor in series, and another branch which appears to be a simple wire (zero resistance).
– In steady state DC, the capacitor acts as an open circuit, meaning the branch containing the 20 ohm resistor and capacitor has effectively infinite resistance to DC current flow.
– The other branch in parallel has zero resistance (a wire).
– Current always follows the path of least resistance. In parallel, a zero-resistance path effectively shorts out any parallel path with resistance. Thus, all the current passing through the 10 ohm resistor will flow through the wire branch, and no current will flow through the branch containing the 20 ohm resistor and capacitor in steady state.
– The equivalent resistance of the parallel combination is 0 ohms.
– The total resistance of the circuit is the sum of the series resistor and the equivalent parallel resistance: R_total = 10 ohms + 0 ohms = 10 ohms.
– The total current flowing from the battery is given by Ohm’s Law: I = V / R_total = 10V / 10 ohms = 1 A. This is the current flowing through the circuit from the battery.

The 20 ohm resistor and the capacitor only influence the current flow during the transient phase when the capacitor is charging. Once the capacitor is fully charged in DC steady state, its branch becomes effectively open circuit, and the parallel wire branch carries all the current.

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45. If an object of mass 10 kg is moving with a uniform speed of 10 m/s, t

If an object of mass 10 kg is moving with a uniform speed of 10 m/s, then the linear momentum and the kinetic energy of the object, respectively, are

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100 N.s and 500 J

100 N.s and 1000 J

200 N.s and 500 J

200 N.s and 1000 J

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We are given the mass and uniform speed of an object and asked to calculate its linear momentum and kinetic energy.

– Linear momentum (p) is given by the product of mass (m) and velocity (v). The unit of linear momentum is kg.m/s, which is equivalent to N.s (Newton-second).
Given m = 10 kg and v = 10 m/s,
p = m * v = 10 kg * 10 m/s = 100 kg.m/s = 100 N.s.

– Kinetic energy (KE) is given by the formula 0.5 * m * v². The unit of kinetic energy is Joules (J).
Given m = 10 kg and v = 10 m/s,
KE = 0.5 * 10 kg * (10 m/s)² = 0.5 * 10 kg * 100 m²/s² = 5 * 100 J = 500 J.

Therefore, the linear momentum is 100 N.s and the kinetic energy is 500 J.

Linear momentum is a vector quantity (direction matters), while kinetic energy is a scalar quantity. The N.s unit for momentum comes from the impulse-momentum theorem, where Impulse (Force x time) equals the change in momentum. 1 Newton = 1 kg.m/s², so 1 N.s = (kg.m/s²) * s = kg.m/s.

46. Deficiency of iron causes

Deficiency of iron causes

Anaemia

Scurvy

Rickets

Cholera

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Iron is an essential mineral required for many bodily functions, most notably the synthesis of hemoglobin, the protein in red blood cells that carries oxygen.

– Deficiency of iron leads to decreased production of hemoglobin. This results in a condition called iron-deficiency anaemia, characterized by a reduced number of red blood cells or a reduced amount of hemoglobin in the blood, impairing oxygen transport. Symptoms include fatigue, weakness, and paleness.
– Scurvy is caused by Vitamin C deficiency.
– Rickets is caused by Vitamin D deficiency (leading to impaired calcium and phosphorus absorption).
– Cholera is an infectious disease caused by bacteria, not a nutrient deficiency.

Iron is also important for myoglobin (oxygen storage in muscles), enzyme function, and immune function. Dietary sources of iron include red meat, beans, lentils, and fortified cereals.

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47. Urea is produced by metabolism of

Urea is produced by metabolism of

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Proteins

Carbohydrates

Lipids

Both Proteins and Carbohydrates

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Urea is the main nitrogen-containing metabolic waste product in mammals. It is synthesized in the liver and excreted by the kidneys.

– Urea is produced from the breakdown of amino acids, which are the building blocks of proteins. When proteins are consumed in excess of the body’s needs or when tissues are broken down, the amino groups from amino acids are removed (deamination). These amino groups are converted into ammonia, which is toxic. The liver then converts ammonia into urea through the urea cycle.
– Carbohydrates and lipids are primarily metabolized for energy, producing carbon dioxide and water as waste products, not significant amounts of nitrogenous waste like urea.

Elevated levels of urea in the blood (azotemia or uremia) can indicate kidney dysfunction, as the kidneys are responsible for filtering urea out of the blood.

48. Which one of the following pairs of enzymes do not work at acidic pH ?

Which one of the following pairs of enzymes do not work at acidic pH ?

Trypsin and Pepsin

Chymotrypsin and Pepsin

Trypsin and Amylase

Pepsin and Amylase

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Enzymes have optimal pH ranges at which they function effectively. Different enzymes in the digestive system operate at different pH levels corresponding to the environment in which they are found. We need to identify the pair of enzymes that do not function in an acidic environment.

– Pepsin is a protease found in the stomach, which has a highly acidic pH (around 1.5-2.5) due to the secretion of hydrochloric acid. Pepsin has an optimal pH in this acidic range.
– Trypsin and Chymotrypsin are proteases found in the small intestine, where the environment is alkaline (pH around 8) due to the secretion of bicarbonate from the pancreas. They do not work at acidic pH.
– Amylase (like salivary amylase and pancreatic amylase) works best at neutral to slightly alkaline pH (around 6.7-7.0 for salivary, around 8 for pancreatic). It is largely inactive at acidic stomach pH.
The question asks for the pair of enzymes that *do not* work at acidic pH. Trypsin and Amylase both have optimal pH values in the neutral or alkaline range and are inactive in acidic conditions. Pepsin, however, works at acidic pH.

The pH in different parts of the human digestive system varies significantly. The mouth is near neutral, the stomach is highly acidic, the small intestine is alkaline, and the large intestine is slightly acidic. This variation allows for optimal activity of different digestive enzymes.

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49. Kwashiorkor, a form of malnutrition, is caused by the deficiency of

Kwashiorkor, a form of malnutrition, is caused by the deficiency of

Minerals

Vitamins

Fats

Proteins

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Kwashiorkor is a severe form of malnutrition affecting children, particularly in regions with high rates of poverty and food insecurity. It is characterized by fluid retention (edema), poor growth, and other symptoms.

– Kwashiorkor is primarily caused by a severe deficiency of dietary protein, often occurring even when calorie intake from carbohydrates is relatively adequate.
– Protein is essential for growth, tissue repair, synthesis of enzymes and hormones, and maintaining fluid balance. Its deficiency leads to the characteristic symptoms of kwashiorkor.

Another major form of severe acute malnutrition is marasmus, which is characterized by severe deficiency of both calories and protein, leading to extreme wasting of body fat and muscle. Kwashiorkor and marasmus are sometimes referred to collectively as protein-energy malnutrition (PEM).

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50. Which one of the following statements about the process of photosynthe

Which one of the following statements about the process of photosynthesis is correct ?

Light energy is directly converted to kinetic energy which oxidizes carbon dioxide.

Light energy is directly converted to chemical energy which causes reduction of water.

Chlorophyll absorbs the chemical energy of light which causes oxidation of carbon dioxide.

Chlorophyll absorbs light energy which causes splitting of water molecules and reduction of carbon dioxide.

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Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll pigment. This process involves converting light energy into chemical energy.

– Chlorophyll absorbs light energy from sunlight.
– This light energy is used to split water molecules (photolysis of water) into oxygen, protons, and electrons. This is the oxidation of water.
– The energy captured and the electrons/protons generated are then used to reduce carbon dioxide into glucose (a sugar). This is the reduction of carbon dioxide.
Thus, chlorophyll absorbs light energy which causes splitting of water molecules and reduction of carbon dioxide.

The overall equation for photosynthesis is 6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂. The process occurs in two main stages: the light-dependent reactions (where light energy is captured and water is split) and the light-independent reactions (Calvin cycle, where CO₂ is reduced to sugar).

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