Due to the properties of waves, the shorter the wavelength the easier it should

Question

Due to the properties of waves, the shorter the wavelength the easier it  should be to create a tight, non-expanding beam of wave energy.  Visible-light lasers provide a good example of beams for which the  energy spreads out at a significantly low rate. For example, it is  possible to shine a laser beam from an Earth-based observatory, have it  pass through the Earth's atmosphere, travel to the Moon where it is  reflected from mirrors left on the Moon by the Apollo astronauts, and  then detect the returning beam at the observatory from which it was  launched. This method is used to measure the Earth-Moon distance with  great accuracy.

Suppose that a small helium-neon laser is emitting red visible light with a power of 2.60 mW in a beam that has a DIAMETER of

Explanation / Answer

a. intensity I = power/area = Emax^2/2u0

Emax^2 = 2.6*10^-3* 2* 4pi*10^-7 * 3*10^8 /pi * 1.15*1.15*10^-6

Emax 687 N/C

Erms = 687/1.414 =485.55

b. u =0.5 eo E^2 = 0.5*8.85*10^-12* 485.55^2 = 1.044 *10^-6 J/m^3

c. energy density u = enrgy/volume

3enery = u * v   = 1.044*10^-6 *3.14* 1.15*1.15*10^-6 * 4.1 = 1.77 *10^-11 J

Related Questions

Navigate

• Browse (All)
• Browse D
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.