Doppler effect and Speed of light


by rushikesh
Tags: doppler, effect, light, speed
rushikesh
rushikesh is offline
#1
Nov27-13, 05:08 AM
P: 20
If light from a moving away object, such as a star, would appear red-shifted (and blue in case of approaching object), why don't we conclude that the speed of light is affected from that. Doesn't it mean that since light from a moving away object appear red, then the speed of light with respect to us has reduced (C-V) ?
Phys.Org News Partner Physics news on Phys.org
Physicists design quantum switches which can be activated by single photons
'Dressed' laser aimed at clouds may be key to inducing rain, lightning
Higher-order nonlinear optical processes observed using the SACLA X-ray free-electron laser
phinds
phinds is offline
#2
Nov27-13, 06:07 AM
PF Gold
phinds's Avatar
P: 5,687
No, the FREQUENCY is affected. That's what red/blue shifted means. The speed is unchanged.
DaleSpam
DaleSpam is offline
#3
Nov27-13, 07:07 AM
Mentor
P: 16,477
The frequency and the speed are related by ##v=f\lambda## where ##\lambda## is the wavelength. With light ##\lambda## changes as the reciprocal of ##f##, so ##v## remains constant.

rushikesh
rushikesh is offline
#4
Nov27-13, 08:22 AM
P: 20

Doppler effect and Speed of light


Quote Quote by DaleSpam View Post
The frequency and the speed are related by ##v=f\lambda## where ##\lambda## is the wavelength. With light ##\lambda## changes as the reciprocal of ##f##, so ##v## remains constant.
So, this must be true even in case of sound. So, does the speed of sound also remain constant in such case?
Bandersnatch
Bandersnatch is offline
#5
Nov27-13, 08:25 AM
P: 557
When a car passes you by, and you hear the pitch of its engine's sound change, do you conclude the speed of sound in the air changed at that moment?
DaleSpam
DaleSpam is offline
#6
Nov27-13, 08:35 AM
Mentor
P: 16,477
Quote Quote by rushikesh View Post
So, this must be true even in case of sound. So, does the speed of sound also remain constant in such case?
Yes, the speed of sound depends on the properties of the air (temperature, density, velocity, etc.), not the speed of the emitter. Two different emitters, one stationary and one moving but otherwise identical, will produce sound waves at different frequencies and wavelengths, but the same speed.


Register to reply

Related Discussions
speed of light is constant because of doppler effect? Special & General Relativity 23
Doppler Effect: can light waves have different effects, depending on your speed? Classical Physics 1
Doppler effect of light General Physics 5
Doppler effect in light General Physics 9
Light Doppler Effect General Astronomy 2