UGC NTA NET/JRF Exam, Environmental Sciences, January-2025

Albedo is the fraction of solar energy (shortwave radiation) reflected from the Earth back into space.

It is a dimensionless value between 0 and 1, often expressed as a percentage. Surfaces with high albedo reflect most of the sunlight, while those with low albedo absorb more.

A. Pure, Fresh Snow: Reflects 80-95% of incoming sunlight, making it one of the highest albedo surfaces on Earth due to its bright white colour and fine crystalline structure that scatters light efficiently.

B. Pure, Old Snow: Slightly less reflective, typically with an albedo of 50-70%, because aging, dust deposition, and partial melting reduce its whiteness and increase absorption.

C. Ice: Has a lower albedo than snow, ranging from 30-40%. It appears darker and smoother than snow, absorbing more sunlight, especially if it has surface water or impurities.

D. Desert: Sandy surfaces reflect about 25-30% of sunlight. While relatively lightcoloured, deserts also absorb substantial heat, particularly where rock or dark soils are exposed.

E. Savanna: Covered with grass and scattered trees, savannas have a lower albedo around 15-20% due to darker vegetation and soil, leading to more absorption of heat.

Thus, the correct decreasing order based on albedo is:
Fresh Snow > Old Snow > Ice > Desert > Savanna.

The Shannon-Weaver Diversity Index (H') isa widely used ecological metric that assesses biodiversity by considering two critical components:

A. Species Richness: This refers to the number of different species present in a community. A more diverse ecosystem will have more species.

D. Equitability (Evenness): This measures how evenly the individuals are distributed across the different species. A community where all species have equal representation has high evenness.

The formula used is:
H' = -∑(pᵢ, x In pᵢ)
where p, is the proportion of individuals in the i-th species.
The index does not distinguish between endemic or invasive species (so B and C are incorrect).
It also does not measure genetic diversity directly (E is also incorrect).

Hence, only richness (A) and equitability (D) are valid components, making option 3 correct.

The question involves correctly identifying terms related to atmospheric moisture and energy fluxes:

A. Mixing Ratio (IV): Defined as the mass of water vapour per unit mass of dry air. It is commonly used in meteorology due to its conservative properties during air parcel ascent or descent.

B. Specific Humidity (III): This is the mass of water vapour per unit mass of moist air (i.e., dry air + water vapour). It remains nearly constant as long as there is no condensation or evaporation.

C. Absolute Humidity (II): Defined as the mass of water vapour per unit volume of air. It changes with temperature and pressure, making it less reliable for atmospheric studies.

D. Bowen Ratio (1): This ratio compares sensible heat flux to latent heat flux at the Earth's surface. A high Bowen ratio implies more energy is used to warm the air than to evaporate moisture, common in arid areas.

So the correct match of terms to definitions is: A-IV, B-III, C-II, D-I.

The concentration of dissolved oxygen (DO) in lake water is strongly influenced by its trophic state, which reflects nutrient enrichment and biological activity.

D. Hypereutrophic lakes: Extremely nutrientrich, with excessive algal blooms and high microbial activity leading to massive oxygen consumption. DO is often depleted, especially in deeper waters.

B. Eutrophic lakes: High nutrient levels, increased productivity, and frequent oxygen depletion in bottom layers due to microbial decay of organic matter.

C. Mesotrophic lakes: Intermediate conditions with moderate biological activity and relatively balanced oxygen levels.

A. Oligotrophic lakes: Deep, nutrient-poor, and typically oxygen-rich throughout the water column due to low biological demand and effective mixing.

Thus, increasing order of DO concentration is: Hypereutrophic < Eutrophic < Mesotrophic < Oligotrophic, i.e., D, B, C, А.

Tidal Range is a vertical measurement of the difference between the height of a high tide and the following low tide. It reflects how much the sea level changes due to the gravitational forces exerted by the moon and the sun.

• Tidal range varies with location and lunar cycle. For example, during spring tides (full/ new moon), the range is largest. During neap tides (first/third quarter), the range is smallest.

• For instance, if high tide is 4.8 m and low tide is 1.3 m, the tidal range = 4.8- 1.3 = 3.5 m.

• This range is important for navigation, fishing, coastal construction, and understanding sediment transport.

Therefore, tidal range is best defined as: The difference in water levels between two consecutive high and low tides.

The sound pressure level (SPL) in decibels from a point source follows the inverse square law, meaning that when the distance from the source increases, SPL decreases logarithmically.
The formula used is:

Two events A and B are independent if the occurrence of one does not affect the probability of the other. This implies:

• P(AB) = P(A) and P(B|A) = P(B)
These are basic identities for independent events. Other expressions like:
• P(AB) = P(A)/P(B) or
• P(B|A) = P(B)/P(A)

The second order moment about the mean is defined as:
μ₂ = El(X - μ)²]
where
• μ = mean of the distribution
• X = random variable
• E = expected value operator
This is by definition the variance of a distribution, representing the average squared deviation from the mean.
So. the second order moment about the mean is equal to the variance.

Albedo is the fraction of solar energy reflected by a surface. The global average albedo is around 0.30 (or 30%).

Now compare:
A. Ice → Albedo around 30-45% or more depending on type and cleanliness.
B. Cumulus Clouds → Very reflective, albedo can range 40-70%, hence higher than global average.
C. Stratus Clouds → Thick cloud layers, albedo 60-90%, much higher than global average.
D. Dark wet Soil→ Low albedo (10-15%), well below global average.
E. Forest → Dense vegetation absorbs much light, albedo ~10-20%.
Hence, only A, B, and C have albedos greater than the global average.

In a hydropower plant, water stored in a reservoir is conveyed to the turbines through large pipes under high pressure. These pipes are called penstocks.

A penstock is a closed conduit that delivers water from the reservoir or forebay to the turbines.

It plays a critical role in converting potential energy into kinetic energy before it strikes the turbine blades.

Other terms:
• Head: vertical height of water
• Reservoir: water storage
• Spillway: safety outlet to discharge excess water
Thus, the correct term for the delivery pipe is Penstock.