- #1

- 55

- 0

I have two questions from the Superposition unit that I don't get it. I'd really any help on these as I have my physics exam on monday! Thanks for any help!

A steel wire is used to stretch a spring. An oscillating magnetic field drives the steel wire back and forth. A standing wave with three antinodes is created wehn the spring is stretched 8.0 cm. What stretch of spring produces a standing wave with two antinodes?

Here's the picture for it:

http://i196.photobucket.com/albums/aa59/aliatehreem/45.jpg [Broken]

λ= 2L/m m=1,2,3 (formula for mth possible wavelength)

I really don't know how to tackle this problem, besides the fact that two antinodes means m=2, and so when I use the wavelength formula (assuming that the wavelength remains constant with al lengths of stretching).

For given info, m=3 and L=0.08 m

λ= 2L/m= 2(0.08)/3 = 0.053 m

Therefore, to solve for the length of the second one,

L=λm/2= 0.053*2/2=0.053 m

However, the answer is actually 0.18 m or 18 cm. I don't think I'm understanding this question properly but I just don't understand the way the problem is set up! Can someone help me please.

The second question from the textbook is:

A 40-cm -long tube has a 40-cm-long insert that can be pulled in and out. A vibrating tuning fork is held next to the tube. As the insert is slowly pulled out, the sound from the tuning fork creates standing waves in the tube when the total length L is 42.5 cm, 56.7 cm, and 70.9 cm. What is the frequency of the tuning fork?

I've drawn the picture here: http://i196.photobucket.com/albums/aa59/aliatehreem/50.jpg [Broken]

λ= 4L/m

f= mv/4L

Would this be an open-closed tube as the tuning fork blocks one side? I don't know if the wavelength remains constant for all three lengths and so I don't know how to tackle this problem. I would really appreciate if anyone could guide me in the right direction!

## Homework Statement

A steel wire is used to stretch a spring. An oscillating magnetic field drives the steel wire back and forth. A standing wave with three antinodes is created wehn the spring is stretched 8.0 cm. What stretch of spring produces a standing wave with two antinodes?

Here's the picture for it:

http://i196.photobucket.com/albums/aa59/aliatehreem/45.jpg [Broken]

## Homework Equations

λ= 2L/m m=1,2,3 (formula for mth possible wavelength)

## The Attempt at a Solution

I really don't know how to tackle this problem, besides the fact that two antinodes means m=2, and so when I use the wavelength formula (assuming that the wavelength remains constant with al lengths of stretching).

For given info, m=3 and L=0.08 m

λ= 2L/m= 2(0.08)/3 = 0.053 m

Therefore, to solve for the length of the second one,

L=λm/2= 0.053*2/2=0.053 m

However, the answer is actually 0.18 m or 18 cm. I don't think I'm understanding this question properly but I just don't understand the way the problem is set up! Can someone help me please.

The second question from the textbook is:

## Homework Statement

A 40-cm -long tube has a 40-cm-long insert that can be pulled in and out. A vibrating tuning fork is held next to the tube. As the insert is slowly pulled out, the sound from the tuning fork creates standing waves in the tube when the total length L is 42.5 cm, 56.7 cm, and 70.9 cm. What is the frequency of the tuning fork?

I've drawn the picture here: http://i196.photobucket.com/albums/aa59/aliatehreem/50.jpg [Broken]

## Homework Equations

λ= 4L/m

f= mv/4L

## The Attempt at a Solution

Would this be an open-closed tube as the tuning fork blocks one side? I don't know if the wavelength remains constant for all three lengths and so I don't know how to tackle this problem. I would really appreciate if anyone could guide me in the right direction!

Last edited by a moderator: