The frequency of light reaching Earth from a particular galaxy is 5% lower than

Question

The frequency of light reaching Earth from a particular galaxy is 5% lower than the frequency the light had when it was emitted.

(a) Is this galaxy moving toward or away from Earth?

away from / toward (pick one)

Explain:

(b) What is the speed of this galaxy relative to the Earth? Give your answer as a fraction of the speed of light.
____ c

(The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is 299,792,458 metres per second (approximately 3.00×108 m/s, or 300,000 km/s (186,000 mi/s))

Explanation / Answer

(a) as the observed frequency is lower, i.e we are seeing the longer wavelength than emitted, which means that distance to be covered increases as the galaxy radiates. Hence, galaxy is moving away from earth.

(b) doppler shift frequency is given by

f' = f (1-b)/(1+b)

Where b = v/c

As f' = 0.95 f (5% lower than original)

0.95 = (1-b)/(1+b)

0.95 + 0.95b = 1 - b

1.95 b = 0.05

b = 0.05/1.95 = 0.02564

Hence, v = 0.02564 c

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.