# Homework Help: Wave Questions

1. Dec 1, 2005

### skyblue112

Hey guys i've got a few questions I didn't know how to do and would appreciate if you could help me out...

A wave generator is used to produce transverse waves in a string that is 12 metres long. Initially, the wave generator is set to a frequency of 5.0 HZ

a) How many wavelengths are being created each minute by the wave generator? (Hint: how many in one second?)

b) What is the period of the wave being gnerated?

c) If the speed of a wave in the string is known to be 15 m/s, what is the length of one wave?

d) The frequency of the wave generator is now changed so that it produces a standing wave pattern along the string. An observer counts 3 nodes along the entire length of the string. What is the frequency of the wave generator when it is producing this standing wave?

I am aware that frequency and periods are inversly related

T = Period
f = frequency

Therefore: T = 1/f & f=1/f

also:

equations we are given to use are:

v= d/t & v=f(wavelength) (velocitiy equals frequency times wavelength.)

Would love some help..

2. Dec 1, 2005

### mezarashi

Did you answer the hint question? If there are 60 seconds in 1 minute, how many seconds are in 1 hour? If there are X waves in 1 second, how many waves are there in 1 minute?

Part b won't be a problem since you have your equations there.

Part c as well ^^

Part d is a standing wave situation. The generator must be generating at the wire's resonant frequency. You'll have to assume that the other end is a fixed end. It's easier to start from finding the resonant wavelength of the third harmonic, or do you remember the equations for this?

3. Dec 1, 2005

### skyblue112

in question a would the answer be?

5 cycles/second = 60 s * 5 cycles/s = 300 cycles a minute
Therefore in question a the wave machine would generate 300 wavelengths per minute

b) T=1/f T=1/5hz T=0.2 seconds Therefore the period is 0.2 seconds

c) I am not exactly sure which equation to use here v=d/t or v=f*(wavelength)

d) I still am unsure of how to start this

4. Dec 1, 2005

### mezarashi

c. What two variables do you have? velocity, frequency, wavelength, distance, time. Pick the right one that would solve.

d. I wouldn't want to give you an equation if you don't know what it means. You can read http://www.cord.edu/dept/physics/p128/lecture99_35.html#topic3 [Broken]

You're looking at a case where one end is open (movable) and the other end is fixed.

Last edited by a moderator: May 2, 2017
5. Dec 1, 2005

### skyblue112

I think I'll leave d and go for help for that tomorrow

its just c

v= 15m/s
wavelength= 300?

if I use v=d/t for question c) then d=t*v

it doesn't work

..... v=f times wavelength then:
wavelength = v/f
wavelength=15m/s*5hz

wavelength = 3m? ^_^

Last edited: Dec 1, 2005
6. Dec 1, 2005

### mezarashi

The equation d = vt should not be new to you. You use it every day in life. If you are driving at 100 miles/hr and going to a nearby city 200 miles away, how long will your journey be? Surely you can figure that out.

The equation $$v = f \lambda$$ can be shown similarly. If you know the wavelength and frequency of the wave, you can find its velocity. Or if you know any 2 of the 3. From your last three lines, I think you have an answer ;)

7. Dec 1, 2005

### skyblue112

i know the v=d/t quite well...its just which to use with each variable...

I understand c.

I would like to thank you for the help once again.

Keep the blue side up.

dt