A ruby laser beam (λ = 694.3 nm) is sent outwards from a 2.7-m diameter telescope to the moon, 384,000 km away. What is the radius of the big red spot on the moon?
A) 500 m
B) 250 m
C) 120 m
D) 1.0 km
E) 2.7 km

Question

Quizplus · Accepted Answer

The radius of the spot on the moon can be determined using the formula:
$r=\frac{1.22\lambda D}{2L}$
where r is the radius of the spot on the moon, λ is the wavelength of the laser beam, D is the diameter of the telescope, and L is the distance to the moon.
Substituting the given values, we get:
$r=\frac{1.22	imes 694.3	imes 10^{-9}	imes 2.7}{2	imes 384,000	imes 10^3}=120$ m
Therefore, the radius of the spot on the moon is 120 m. Thus, the answer is C.

A Ruby Laser Beam (λ = 694