The H_δ line has a wavelength of 410.2 nm when observed in the laboratory. If the H_δ line appears in a stars spectrum at 410.0 nm, what is the radial velocity of the star? A) 146 km/s away from the observer B) 146 km/s toward the observer C) 6.0 × 10⁷ m/s away from the observer D) 6.0 × 10⁷ m/s toward the observer E) The radial velocity of the star cannot be determined from this information.

Question

Quizplus · Accepted Answer

We can use the formula:

Δλ/λ = v/c

where Δλ is the difference between the observed wavelength and laboratory wavelength, v is the radial velocity of the star, and c is the speed of light.

Plugging in the given values, we get:

(410.0 nm - 410.2 nm)/(410.2 nm) = v/c

Solving for v, we get:

v = -146 km/s

The negative sign indicates that the star is moving toward the observer. Therefore, the best choice is B.

The H δ Line Has a Wavelength of 410

The H_δ Line Has a Wavelength of 410