Physics quiz question: comparing blue, yellow laser frequencies

Physics 205B Quiz 1, spring semester 2020
Cuesta College, San Luis Obispo, CA

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Blue laser light has a wavelength of 445 nm light in air, while yellow laser light has a wavelength of 594 nm in air. The __________ laser light has a higher frequency in air.
(A) blue.
(B) yellow.
(C) (There is a tie.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (A)

Wave speed v depends on the properties of the medium. Frequency f depends on the properties of the source. These two parameters can be varied independently of each other.

The wavelength λ is the parameter dependent on both of the independent parameters:

λ = v/f.

Since the two laser light colors have the same speed v (as they travel through the same medium), then because of their different frequencies, they will have have different λ wavelengths (as this parameter depends on both the wave source and the properties of the medium):

λ₁ = v₁/f₁,

λ₂ = v₂/f₂,

where λ₁ < λ₂, as blue light (here, λ₁) has a much shorter wavelength than yellow light (here, λ₂). Since v₁ = v₂ (as both forms of laser light travel through the air), then f₁ > f₂, and thus blue laser light has a higher frequency than yellow laser light.

Sections 30882, 30883
Exam code: quiz01PxP7
(A) : 22 students
(B) : 8 students
(C) : 5 students
(D) : 0 students

Success level: 63%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.67