You are Here: Home >< Physics

# Waves/harmonic question

Announcements Posted on
Why bother with a post grad? Are they even worth it? Have your say! 26-10-2016

Paper 1, Question 7.3

I have no idea what they are doing in that one, so any help will be appreciated (and in as much simplicity as possible )
2. (Original post by 123chem)

Paper 1, Question 7.3

I have no idea what they are doing in that one, so any help will be appreciated (and in as much simplicity as possible )
Will walk you through it as a simpleish derivation:

the relationship between the speed of a wave, it's frequency and wavelength is:

from Newton's second law and some approximations (not going to walk you through this bit as it is complicated so just take the result as a given) the speed of a wave on a string is related to the tension,mass and length of a string by:

combining these gives us:

We can rearrange this to get:

we will now define where is the distance between the two fixed points (in this case X and Y). This relates the length between the points and the FUNDAMENTAL wavelength. Since we are using the fundamental wavelength, it also follows that we must use the fundamental frequency. (take it as a given that the tension remains the same regardless which mode we are in).

We can see from the diagram that we are in mode 3. The distance XY is given as 0.66m. We can calculate the fundamental frequency as:

substituting in our relation between the fundamental wavelength and the distance XY into our earlier relation we also find that:

we know the values of , , and and can plug these into our equation to get:

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: May 24, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### Who is getting a uni offer this half term?

Find out which unis are hot off the mark here

### Brexit: Why you should study law

Poll
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.