Question

In hydrogen, the transition from level 2 to level 1 has a rest wavelength of 121.6 nm n m . Suppose you see this line at a wavelength of 120.5 nm n m in Star A, at 121.2 nm n m in Star B, at 121.9 nm n m in Star C, and at 122.9 nm n m in Star D. Which stars are coming toward us?

Answer 1

Answer:

$- 2.71 \times {10}^{6} \: toward \: us$

$9.872 \times {10}^{5} away \: from \: \: us$

Explanation:

$\delta \lambda = \lambda \frac{v}{c} \\ v = \frac{ \lambda_{f} - \lambda}{ \lambda} c$

A:

$v = \frac{120.5 nm - 121.6nm}{121.6nm} \times 3 \times {10}^{8}m {s}^{ - 1} \\ = - 2.71 \times {10}^{6} m {s}^{ - 1}$

B:

$v = \frac{112nm - 121.6nm}{121.6nm} (3 \times {10}^{8} m {s}^{ - 1} ) \\ = 9.872 \times {10}^{5} m {s}^{ - 1}$