Question

1) Consider the following questions

a) Light takes 8 minutes and 19 seconds to reach from the sun to the earth. The speed of light is 3.0x10^8 m/s. How far (in meters) away is the earth from the sun?

b) Energy from the sun goes everywhere. What is the surface area of sphere with a radius of Earth’s orbit? (A=4 pi r²)

c) What is the surface area of your pupil in m²?

d) What is the ratio of the surface area of the sphere with a radius the size of Earth’s orbit to the surface area of your pupil?

e) If 1.2x10^34 J of energy are released by the sun in a year, how much of it enters your eye if you stare directly at the sun for 6 minutes?

Answer #1

a)

We know speed = distance / time

We know the speed and time (in min).

Solution :

Conversion of time to second

Time conversion

8 min+19 second = 8 x 60 s + 19 s = 499 s

Distance = speed x time = 3.0E8 m/s x 499 s = 1.50 E 11 m

b) In order to calculate are of surface of earth we need the radius of earth.

Radius of earth is 6371000 m

Aread of earth = 3.14 x 4 x ( 3671000m)^{2} = 5.098 E14
m^{2}

c) Surface area of pupil

radius of pupil is 2 mm and so area

= 4 x 3.14 x ( 2 E-3 m )^{2}

= 5.024 E -5 m^{2}

d)

Ratio of surface area of size of earth orbit to the surface area of pupil

= 5.098E14 m^{2}/ 5.04E-5 m^{2}

= 1.014 E19

e)

energy absorbed by eye = 1.2 E34 x (5.024 m^{2}
/5.098E14 )x 6 x 60 s

= 4.26 E17 J

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