Question

The value of solar constant is approximately:
A. $1340\,watt/{m^2}$
B. $430\,watt/{m^2}$
C. $340\,watt/{m^2}$
D. $1388\,watt/{m^2}$

Answer 1

First let us see what is meant by solar constant-
The solar constant is the mean amount of radiant energy that the atmosphere derives from the sun.
It is more reliably measured from satellites where atmospheric interference is absent.

Complete step by step solution:
The solar constant has a value of roughly $1.366\,kilowatts$ per square metre. The constant is fairly consistent, rising at the height of a $11$ year solar cycle by just $0.2$ percent.
Sunspots obstruct the light and minimise the emission by a few tenths of a percent, but there are more widespread and longer-lived bright spots, called plages, correlated with solar activity, so their visibility compensates for the darkness of the sunspots.
For the study of heat-exchange processes in the earth’s atmosphere and for the analysis of processes occurring in the sun, knowledge of the exact value of the solar constant is very important. This approach allows for the absorption and dispersion of sunlight into the atmosphere of the earth to be taken into consideration.
Because of the earth’s slightly elliptical path around the sun, the solar constant generally changes by $+ / - 3$ percent. When the planet is at the perihelion (first week of January) and when the planet is at the aphelion, the Sun-earth difference is greater.
Hence, the value of solar constant is approximately $1388\,watt/{m^2}$ .
So, option D is correct.

Note:
The solar constant includes every radiation except those of visible rays. The solar constant can also be measured in calories per minute per square centimetre as $1388\,watt/{m^2} = 1.94\,cal/cm \times \min$. Also the earth should be at an average distance from the Sun while measuring the solar constant.