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NCERT Solutions for Class 7th Science Chapter 7 .2.1 Land and Sea Breeze — Activity 7.4: Let us investigate

Book page 94–957 Updated on2026-09-19

Q1.
Measure the temperature of soil and water every 5 minutes and record the data in Table 7.4.
Table 7.4: Temperature of soil and water when heated
S.No.Time (min)Temperature of soil (°C)Temperature of water (°C)
1.0  
2.5  
3.10  
4.15  
5.20  
Table 7.4 as printed on page 95 — the times are given, the two temperature columns are blank.
Answer

Two identical bowls, one half filled with soil and one half filled with water, are kept side by side in bright sunlight with a laboratory thermometer in each (Fig. 7.6). A typical set of readings taken on a clear, sunny day looks like this.

Table 7.4: Temperature of soil and water when heated
S.No.Time (min)Temperature of soil (°C)Temperature of water (°C)
1.03030
2.53431
3.103832
4.154133
5.204434
Check it yourself: your own numbers will be different — they depend on the day, the place and the time. What must come out the same is the pattern: the soil column climbs much faster than the water column. Record your own readings; do not copy these.
Care while measuring: keep the bulb of each thermometer fully buried in the soil and fully dipped in the water, and make sure it does not touch the bottom or the sides of the bowl — otherwise you measure the temperature of the bowl, not of the soil or the water.
Q2.
Did the temperature rise by the same amount for both the soil and the water at the same time?
Answer

No. In the same interval of time, the temperature of the soil rises much more than the temperature of the water.

With the readings above, after 20 minutes in the same sunlight:

Rise in temperature of soil = 44 °C − 30 °C = 14 °C
Rise in temperature of water = 34 °C − 30 °C = 4 °C
Why it happens: both bowls receive the same amount of heat from the Sun, but water needs far more heat than soil to raise its temperature by one degree. So the same heat produces a big rise in the soil and only a small rise in the water.
Q3.
If not, which one got heated faster?
Answer

The soil got heated faster.

Why it matters: this single fact explains the whole of the next section. Land (soil, sand, rock) heats up faster than water during the day — and, as the book goes on to show, it also cools down faster at night. That difference is what creates sea breezes and land breezes along a coast.
Did you know? The same property makes a beach at noon unbearable to walk on barefoot while the sea water just a few steps away still feels cool.
Q4.
How much was the rise in temperature of the soil and the water in 20 minutes?
Answer

Using the sample readings of Table 7.4 (both started at 30 °C):

Soil: 44 °C − 30 °C = 14 °C
Water: 34 °C − 30 °C = 4 °C
Difference = 14 °C − 4 °C = 10 °C

So in the same 20 minutes and the same sunshine, the soil became about 10 °C hotter than the water did — the soil heated up roughly three to four times as much.

Tip: always subtract the reading at 0 minutes from the reading at 20 minutes. The rise in temperature is what matters here, not the final temperature.
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