A distant star system is discovered in which a planet with
twice the radius of the earth and rotating 3.0 times as fast as the
earth orbits a star with a total power output of .
a. If the star’s radius is 6.0 times that of the sun, what is the
electromagnetic wave intensity at the surface? Astronomers
call this the surface flux. Astronomical data are provided
inside the back cover of the book.
b. Every planet-day (one rotation), the planet receives .
of energy. What is the planet’s distance from its star? Give
your answer in astronomical units (AU), where 1 AU is the
distance of the earth from the sun.
a. The wave intensity at the surface is
b. The planet's distance from its star is,
The radius of the star is 6 times of the radius of the sun that is,
The power output of the star,
Consider the energy radiation in spherical symmetry, the intensity of the EM wave at the surface is,
The energy from the star will be radiated into the space equally in all directions. The ratio of the power output by
the star to the power falling on the planet’s surface is equal to the ratio of the surface area of a sphere with radius
equal to the planet’s orbital radius to the cross-sectional area of the planet that can be considered as a disc.
The planet completes one full rotation 3 times faster than the earth. So, the time taken by the planet to complete a rotation is,
Energy received by the planet is, role="math" localid="1649875552528"
According to the question,
LASIK eye surgery uses pulses of laser light to shave off tissue
from the cornea, reshaping it. A typical LASIK laser emits a
1.0-mm-diameter laser beam with a wavelength of 193 nm. Each
laser pulse lasts 15 ns and contains 1.0 mJ of light energy.
a. What is the power of one laser pulse?
b. During the very brief time of the pulse, what is the intensity
of the light wave?
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