# Energy Engineering Questions and Answers – Solar Constant

This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Solar Constant”.

1. The amount of energy received in unit time on a unit area perpendicular to the sun’s direction at the mean distance of the earth from the sun is called ________
b) Solar constant
d) Air Mass

Explanation: The amount of energy received in unit time on a unit area perpendicular to the sun’s direction at the mean distance of the earth from the sun is called solar radiation. It is defined as the solar energy receiving at the top of the atmosphere, denoted by Isc.

2. What is ‘n’ in the following solar intensity formula?
I = Isc {1 + 0.033cos (360n/365)}
a) Day of the year
b) Month of the year
c) The year
d) Week of the year

Explanation: The following ‘n’ denotes day of the year in the formula. Since the distance between sun and earth varies, extra-terrestrial flux also varies. Earth is closest to the sun in the summer and farthest away in the winter.

3. When the sun is directly on the top of head, it as referred to _________
a) Zenith
b) Azimuth
c) Declination
d) Hour angle

Explanation: When the sun is directly on the top of the head, it is referred to as sun at zenith. The zenith is an imaginary point directly “above” a particular location, on the imaginary celestial sphere. The zenith is the “highest” point on the celestial sphere.

4. Path length of radiation through the atmosphere to the length of path when the sun is at zenith is called ___________
a) Declination
b) Air mass
c) Azimuth
d) Solar Constant

Explanation: Path length of radiation through the atmosphere to the length of path when the sun is at zenith is called Air mass.
Air mass, m = Cos (altitude angle), except for very low solar altitude angles.
m = 1; When the sun is at the zenith
m = 2; When zenith angle is 60o
m = 3; sec (θz) for m>3.

5. Radiation intensity ‘I’ normal to the surface is given by __________
a) ICosθ
b) Itanθ
c) ICotθ
d) Isinθ

Explanation: I = ICosθ, Let θ = Angle between an incident beam radiation I and the normal to the plane surface. And the θ is referred to as incident angle. And further by this formula latitude angle, declination, hour angle, zenith angle and solar azimuth angles are found out.
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6. Angle made by radial line joining the location to the centre of the earth with the projection of the line on the equatorial plane is called _________
a) Latitude
b) Zenith angle
c) Hour angle
d) Declination

Explanation: Angle made by radial line joining the location to the centre of the earth with the projection of the line on the equatorial plane is called latitude. And it is denoted by Φl. It is also given by the angular distance north or south of the equator measured from the centre of the earth.

7. Angular distance of sun’s rays north or south of the equator is called _______
a) Declination
b) Hour angle
c) Latitude
d) Air mass

Explanation: Declination is the angular distance of sun’s rays north or south of the equator. It is the angle between the line extending from the centre of the sun to the centre of the earth and the projection of this line upon earth’s equatorial plane.

8. By which of the following symbol is solar Declination denoted by ____________
a) δ
b) ρ
c) Δ
d) γ

Explanation: Solar declination is denoted by Greek letter δ(DELTA). Solar declination is the angle between the earth-sun line and the equatorial plane. Solar declination varies throughout the year. And is given by cooper equation,
δ = 23.45sin [(360/365) (284+n)] ∵n is day of the year.

9. The angle through which the earth must turn to bring the meridian of a point directly in sun’s rays is called __________
a) Hour angle
b) Declination
c) Latitude
d) Air mass

Explanation: The angle through which the earth must turn to bring the meridian of a point directly in sun’s rays is called Hour angle. And it is denoted by Greek letter ω (OMEGA). It is measured from noon based on the solar local time (LST).

10. Solar Altitude is also called as ________
a) Declination
b) Altitude angle
c) Zenith angle
d) Azimuth angle

Explanation: The vertical angle between the projection of the sun’s rays on the horizontal plane and the direction of sun’s rays passing through the point s called solar altitude and is also referred to altitude angle and is denoted by Greek letter α (ALPHA).

11. The angle between the sun’s rays and a line perpendicular to the horizontal plane through angle the beam of the sun and vertical is called __________
a) Solar Azimuth angle
b) Zenith angle
c) Altitude angle
d) Declination

Explanation: The angle between the sun’s rays and a line perpendicular to the horizontal plane through angle measured from the north to the horizontal projection of rays is called zenith angle. And it is denoted by θz.

12. The solar angle in degrees along the horizon east or west of north or it is the horizontal angle measured from north to the horizontal projection of sun’s rays is called ___________
a) Solar azimuth angle
b) Zenith angle
c) Altitude angle
d) Declination

Explanation: The solar angle in degrees along the horizon east or west of north or it is the horizontal angle measured from north to the horizontal projection of sun’s rays is called solar azimuth angle. And it is denoted by Greek letter γs (GAMMA).

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