physics question waves

[pizza1994]

The first harmonic for an organ pipe closed at one end is 50 Hz. How long is the pipe? (Use 340 m/s for the speed of sound.)

a) 3.4 m

b) 1.7 m

c) 2 m

I got A) but the answer is B

i dont get this either -_-

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[IslandStyle808]

You probably did the calculation for an open pipe where lambda=2L this will lead you to 3.4m. If you did it with the closed end pipe calculation, lambda=4L, you would get 1.7m. This is why B is correct.

calculations
v= freq. x lambda
lambda = (340m/s)/(50Hz)
lambda = 6.8

lambda = 4L/n
L=(6.8m)(1)/4
L= 1.7m

 

[Cawolf]

Just what @IslandStyle808 said.

I just remember that f = v/2L if both ends are the same and f = v/4L if the ends are different. These formulas being for the first harmonic. They each have a factor of n. If the ends are the same n = 1, 2, 3, ... and if the ends are different then n = 1, 3, 5, . .

 

[pizza1994]

Just what @IslandStyle808 said.

I just remember that f = v/2L if both ends are the same and f = v/4L if the ends are different. These formulas being for the first harmonic. They each have a factor of n. If the ends are the same n = 1, 2, 3, ... and if the ends are different then n = 1, 3, 5, . .

dang it. missed that difference there! thanks

 

[pizza1994]

You probably did the calculation for an open pipe where lambda=2L this will lead you to 3.4m. If you did it with the closed end pipe calculation, lambda=4L, you would get 1.7m. This is why B is correct.

calculations
v= freq. x lambda
lambda = (340m/s)/(50Hz)
lambda = 6.8

lambda = 4L/n
L=(6.8m)(1)/4
L= 1.7m

thanks. stinkin closed end pipe