Does anyone have a good way of remembering this formula and the sign conventions (how to choose the sign)?
For some reason I get this damn formula's signs mixed up
For some reason I get this damn formula's signs mixed up
Doppler Effect
- Thread starter DrSwede
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f'=f(V+- Vd)/V-+Vs)
think of it this way, when you hear a siren from a firetruck, the closer they get, the louder they are. So based on that it means their frequency is increasing.
so this means f' > f. In order for that to happen, (V+-Vd)/(V-+Vs) has to be greater than 1, and only the top signs will guarntee that.
Sorry, that's the best I can do.
you can try this equation that may be easier to remember
(delta f)/f =-v/c where's c is the speed of the wave and v is the delta v between detector and source.
think of it this way, when you hear a siren from a firetruck, the closer they get, the louder they are. So based on that it means their frequency is increasing.
so this means f' > f. In order for that to happen, (V+-Vd)/(V-+Vs) has to be greater than 1, and only the top signs will guarntee that.
Sorry, that's the best I can do.
you can try this equation that may be easier to remember
(delta f)/f =-v/c where's c is the speed of the wave and v is the delta v between detector and source.
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I also think of examples: firetruck coming. if you're not moving, that means Vd = 0. Now you have f' = f(v/(v+- vs)) to pick + or -, just think which will give u a value that will increase ur f. v/small or v/big. here it's v/small, which means it's v- vs.
just know like 2 situtations and elaborate it onto the others.
i remember encountering some mediocre hard questions in the princeton review science workbook. talking about a speeding trucker passing by a cop with a doppler effect gun, given speed of the trucker, u gotta find frequency heard by the cop from the moving truck.
Trick to it is you have to realize frequency recieved by the trucker is gonna be increased. and how it's projected out of the trucker is also gonna increase by the time it reaches the cop. so u gotta do the formula twice!!!!
just know like 2 situtations and elaborate it onto the others.
i remember encountering some mediocre hard questions in the princeton review science workbook. talking about a speeding trucker passing by a cop with a doppler effect gun, given speed of the trucker, u gotta find frequency heard by the cop from the moving truck.
Trick to it is you have to realize frequency recieved by the trucker is gonna be increased. and how it's projected out of the trucker is also gonna increase by the time it reaches the cop. so u gotta do the formula twice!!!!
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hey guys,
i think you've got the doppler effect nailed for frequency...
but I never know when they ask questions about WAVELENGTH what to do...
are there any equations for this? so you just plug in wavelength*f=v and if so don't you get too many variables...its all too confusing
any help out there?
i think you've got the doppler effect nailed for frequency...
but I never know when they ask questions about WAVELENGTH what to do...
are there any equations for this? so you just plug in wavelength*f=v and if so don't you get too many variables...its all too confusing
any help out there?
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Dude, just stick on a "v/" for both sides of the equation.
so u end up with lamda= v/f` = v/f ((v +- vd)/(v -+ vs))^-1
and most likely they will give u vs and let u solve. or they will ask u to solve for factors of v.
so u end up with lamda= v/f` = v/f ((v +- vd)/(v -+ vs))^-1
and most likely they will give u vs and let u solve. or they will ask u to solve for factors of v.
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