Q1.
Complete Table 13.1 using information from authentic sources like websites and books. (Table 13.1: Reflection of solar radiation by surfaces of materials — Snow 0.80 – 0.90; Ice 0.50 – 0.70; Crushed rock 0.25 – 0.30; Light coloured soil; Black soil; Ocean water)
Answer
The three missing rows, taken from standard published albedo tables:
| S. No. | Material | Albedo | What it means |
|---|---|---|---|
| 1. | Snow | 0.80 – 0.90 | Reflects 80 – 90% — stays very cold (printed in the book) |
| 2. | Ice | 0.50 – 0.70 | Reflects about half to two-thirds (printed in the book) |
| 3. | Crushed rock | 0.25 – 0.30 | Reflects about a quarter (printed in the book) |
| 4. | Light coloured soil | 0.30 – 0.40 | Pale, dry, sandy soil — reflects roughly a third |
| 5. | Black soil | 0.05 – 0.15 | Dark regur soil absorbs almost everything, so it heats fast |
| 6. | Ocean water | 0.06 – 0.10 | With the Sun high, water reflects only about 6% and absorbs the rest |
Why the pattern goes this way: albedo is the fraction of solar radiation a surface reflects. A surface that reflects little must absorb a lot, and absorbed radiation is what raises temperature. So a high albedo surface stays cool and a low albedo surface heats up. Whiteness and smoothness raise albedo; darkness and roughness lower it. This is why snow-covered polar regions remain intensely cold — they turn most of the incoming energy straight back to space — and why black cotton soil and the open ocean are comparatively warm.
If insolation on a surface = 1000 W m–2,
Energy absorbed = (1 – albedo) × insolation
Snow (a = 0.85): absorbed = (1 – 0.85) × 1000 = 150 W m–2
Black soil (a = 0.10): absorbed = (1 – 0.10) × 1000 = 900 W m–2
Six times as much energy into the black soil, from exactly the same Sun.
Energy absorbed = (1 – albedo) × insolation
Snow (a = 0.85): absorbed = (1 – 0.85) × 1000 = 150 W m–2
Black soil (a = 0.10): absorbed = (1 – 0.10) × 1000 = 900 W m–2
Six times as much energy into the black soil, from exactly the same Sun.
Did you know? Albedo makes a feedback loop in the Arctic. Sea ice (high albedo) melts to expose ocean water (low albedo); the ocean absorbs more radiation, warms, and melts more ice. This ice–albedo feedback is one reason the polar regions are warming faster than the rest of the planet. Ranges are quoted because albedo depends on the Sun's angle, on how wet the soil is, and on how fresh the snow is.