Question

For a specific wavelength 670 nm of light from a galaxy moving with velocity ν, the observed wavelength is 670.7 nm. The value of ν is

• A. 3 × 108 ms-1
• B. 3 × 1010 ms-1
• C. 3.13 × 105 ms-1
• D. 4.48 × 105 ms-1

Answer 1

Answer: (C)

3.13 × 105 ms-1

Answer 2

The correct answer is (C) : 3.13 × 105 ms–1

λobs = λsource $\sqrt{\frac{1+\frac{ν}{C}}{1-\frac{v}{C}}}$
For ν << C,
$\frac{670.7}{670}$ = 1 + $\frac{ν}{C}$
⇒ ν = $\frac{0.7}{670}$ × 3 × $10^8$ m/s
⇒ ν ≃ 3.13 × $10^5$ m/s