# Heat Transfer Questions and Answers – Solar Radiations

This set of Heat Transfer Multiple Choice Questions & Answers (MCQs) focuses on “Solar Radiations”.

1. The heat energy absorbed by a known area in a fixed time is determined with the help of an instrument called
a) Psychrometer
b) Pyrheliometer
c) Thermometric well
d) Any instrument

Explanation: The effects of absorption by the atmosphere are eliminated by finding the value of the solar constant at various altitudes of the sun on the same day.

2. The observed solar constant S0, the true solar constant S and the angular elevation Z of the sun are related by the expression
a) S0 =S a SEC Z
b) S0 =2 S a SEC Z
c) S0 =3 S a SEC Z
d) S0 =4 S a SEC Z

Explanation: From the straight line graph between log S0 along y-axis and sec Z along x-axis, the intercept log S on the y-axis is found.

3. The value of solar constant varies between
a) 1123 and 1237 W/m2
b) 1345 and 1453 W/m2
c) 1987 and 2346 W/m2
d) 1335 and 1815 W/m2

Explanation: When the sun lies at a mean distance from the earth, the heat flux from the sun to the outer edge of the atmosphere has been found to be 1350 W/m2.

4. The total amount of heat energy received by the sphere of radius r is
a) 2 π R2 S
b) 6 π R2 S
c) 4 π R2 S
d) π R2 S

Explanation: Area of sphere is 4 π R2.

5. Amount of heat energy radiated by unit surface of the sun in the same time workout as
Take, R = mean distance of earth from the sun and r = radius of sun
a) E = π R2 S/4 π R2
b) E = 4 π R2 S/4 π R2
c) E = 4 π R2
d) E = 4 π R2 S

Explanation: It is the ratio of 4 π R2 S to 4 π R2.
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6. Temperature of sun can be workout from
a) Wein’s displacement law
b) Stefan-Boltzmann law
c) Kirchhoff’s law
d) All of the Mentioned

Explanation: (Wavelength) MAX T = 2-89 * 10 -3 m K.

7. The temperature of the photosphere, referred to as the effective temperature of the sun, is usually taken as
a) 3000 K
b) 4000 K
c) 5000 K
d) 6000 K

Explanation: The sun consists of a central hot portion surrounded by the photosphere.

8. The approximate distribution of the flow of sun’s energy to the earth’s surface is
a) 53% is reflected back to space
b) 53% is transmitted to the earth
c) 9% is scattered
d) 22% is absorbed in the atmosphere

Explanation: 33% is reflected back to space, 15% is absorbed in the atmosphere and 43% is transmitted to the earth.

9. The solar radiation that is felt at the earth’s surface includes
(i) Direct radiation that has passed through the atmosphere
(ii) Diffuse radiation from the sky
(iii) Absorbed radiation from the water
Identify the correct statement
a) i only
b) i and ii
c) i, ii and iii
d) ii and iii

Explanation: Option (iii) must be reflected radiation from water.

10. When the sun lies at a mean distance from the earth, the heat flux from the sun to the outer edge of the atmosphere has been found to be
a) 2350 W/m2
b) 3350 W/m2
c) 4350 W/m2
d) 1350 W/m2

Explanation: 47% of this would reach the earth’s surface.

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