A particular spectral line from an observed object is measured to be at a wavelength of 400 nm. that same spectral line is found to have a wavelength of 800 nm when measured at rest in the lab. what is the radial velocity of the observed object?

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Physics

Smiley

10 November, 22:18

A particular spectral line from an observed object is measured to be at a wavelength of 400 nm. that same spectral line is found to have a wavelength of 800 nm when measured at rest in the lab. what is the radial velocity of the observed object?

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Isabel Fisher · Answer 1

To find the radial velocity of the object we are going to apply the regular Doppler formula:

[measured wavelenght - rest wavelenght / rest wavelenght] = V/C, where V is the radial velocity and C is the speed of light which is equal to 300,000km/sec.

[400 - 800/800] = V/300,000 = - 150,000.

This means that the object is moving at a velocity of 150,000km/sec toward the observer.

The minus sign infront of the answer indicates that the object is moving towards the observer while a positive value will indicate that the object is moving away from the observer.