Question

The H-alpha spectral line normally has a wavelength of 656 nm in the lab. If we observe the following wavelengths in different objects, which one is receding from us the fastest?

a. 710 nm

b. 625 nm

c. 687 nm

d. 486 nm

Answer 1

The object with an observed H-alpha spectral line at 710 nm is receding from us the fastest, as it shows the greatest redshift compared to the rest wavelength of 656 nm.

Step-by-step explanation:

The student's question pertains to the Doppler effect in light, which causes the wavelengths of light from objects moving away from an observer (such as Earth) to appear longer (redshifted), and those from objects moving towards an observer to appear shorter (blueshifted). The H-alpha spectral line has a known rest wavelength of 656 nm. When we observe different wavelengths, we can determine the relative motion of the object emitting the light.

To identify which object is receding from us the fastest, we need to compare the observed wavelengths to the rest wavelength. The largest increase indicates the greatest speed away from us. In the given options:

• Option a (710 nm) shows the greatest increase from the rest wavelength.

Therefore, the object with the observed wavelength of 710 nm is receding from us the fastest.