I'm confused, what is the difference between the distance a wave travels and the wavelength. My textbook tells me speed =wavelength/time period.
The question is the frequency of a soundwave is 50Hz, represented as a transverse wave find:
a) How many waves are emitted in 20 seconds. It's 50*20 =1000 correct?
b) The wavelength has changed to 20cm. how far does the wave travel in 20 seconds, I really don't understand this part.
c)Speed of the wave, doesn't provide context, I assumed it is the speed of the wave with a wavelength of 20 cm but both to be on the safe side.

Primus2x
 Follow
 0 followers
 2 badges
 Send a private message to Primus2x
 Thread Starter
Offline2ReputationRep: Follow
 1
 24032013 20:49

 Follow
 2
 24032013 21:33
Wavelength is the distance between one peak of the wave and the next. Wavelength doesn't tell you anything about how far the wave has travelled or will travel.
Are you sure you're not misquoting the question?
You can calculate a wave speed if you know what the wavelength and frequency are at the same time.
But if the question is saying the wavelength changes without giving you the new frequency you don't have enough to work out the speed. 
Primus2x
 Follow
 0 followers
 2 badges
 Send a private message to Primus2x
 Thread Starter
Offline2ReputationRep: Follow
 3
 24032013 21:42
What other information is needed to calculate how far a wave has travelled in a given amount of time?

Floydacious
 Follow
 3 followers
 9 badges
 Send a private message to Floydacious
Offline9ReputationRep: Follow
 4
 24032013 21:50
What medium are the waves travelling in and at what temperature? Sound waves travel at different speeds in different mediums and temperatures.
A) The amount of waves depends on how much is emitted from the source. I don't exactly understand a question, a better question would be what you have in b, how far has it travelled in 20 seconds.
B) If the wavelength has changed to 20cm, that means the frequency has changed.
C) This depends entirely on the medium the wave is travelling in and at what temperature. This refers back to my first sentence. 
Primus2x
 Follow
 0 followers
 2 badges
 Send a private message to Primus2x
 Thread Starter
Offline2ReputationRep: Follow
 5
 24032013 22:08
a) f=50Hz, T=20, find the number of waves emitted
b) wavelength =20cm (I found this contradictory with part a so I assumed it entered a new medium, is this not the case?), find how far it has travelled in 20s
c)Find the speed 
 Follow
 6
 24032013 22:39
(Original post by Primus2x)
a) f=50Hz, T=20, find the number of waves emitted
b) wavelength =20cm (I found this contradictory with part a so I assumed it entered a new medium, is this not the case?), find how far it has travelled in 20s
c)Find the speed 
Primus2x
 Follow
 0 followers
 2 badges
 Send a private message to Primus2x
 Thread Starter
Offline2ReputationRep: Follow
 7
 24032013 22:50
(Original post by Joinedup)
TBH this would probably work much better if you gave us the exact text of the question instead of inviting us to interpret your interpretation of it.
10 A source of waves has a frequency of vibration of 50Hz.
a) How many complete waves are emitted in 20s?
b)The wavelength is 20cm, how far has the wave travelled in 20s?
c)Calculate the speed of the wave. 
RVNmax
 Follow
 15 followers
 18 badges
 Send a private message to RVNmax
 Study Helper
Offline18ReputationRep:Study Helper Follow
 8
 25032013 00:17
(Original post by Primus2x)
I'm confused, what is the difference between the distance a wave travels and the wavelength. My textbook tells me speed =wavelength/time period.
The question is the frequency of a soundwave is 50Hz, represented as a transverse wave find:
a) How many waves are emitted in 20 seconds. It's 50*20 =1000 correct?
b) The wavelength has changed to 20cm. how far does the wave travel in 20 seconds, I really don't understand this part.
c)Speed of the wave, doesn't provide context, I assumed it is the speed of the wave with a wavelength of 20 cm but both to be on the safe side.
a) the Time period of a wave,T, is 1/frequency. so do you think you were correct?
(Original post by Primus2x)
Very well
10 A source of waves has a frequency of vibration of 50Hz.
a) How many complete waves are emitted in 20s?
b)The wavelength is 20cm, how far has the wave travelled in 20s?
c)Calculate the speed of the wave.(Original post by Primus2x)
What other information is needed to calculate how far a wave has travelled in a given amount of time?
c) since they have only given you one wavelength, yes I would assume you need to use that one only.
Think about it and get back to me(quote me)
I hope I could help! 
Primus2x
 Follow
 0 followers
 2 badges
 Send a private message to Primus2x
 Thread Starter
Offline2ReputationRep: Follow
 9
 25032013 09:57
(Original post by RVNmax)
Pretend a wave is your finger that you will move in a straight line. the wavelength can represent the length of your finger/wave. Then the distance the wave travels is how much you move your finger .
a) the Time period of a wave,T, is 1/frequency. so do you think you were correct?
(Original post by RVNmax)
b) You didn't know the wavelength before so now they are telling you. Clue is your own post: what else do you think is needed to work out distance traveled during a specific time which they have given you?
(Original post by RVNmax)
c) since they have only given you one wavelength, yes I would assume you need to use that one only.
Think about it and get back to me(quote me)
I hope I could help!
So this all depends on part a) being correct. 
 Follow
 10
 25032013 10:47
f=50hz so in one second you get 50 complete wave cycles, peak and trough. The waves move away from the source at an unknown speed.
The distance between peaks (wavelength) is 0.2 meters.
The distance covered by one seconds worth of waves is the wavelength multiplied by the number of waves emitted in a second. I.e. At the instant you finish emitting the 50th peak, the first peak is 50*0.2 meters away.
It took one second to emit those 50 complete wave cycles.
Distance per second is a speed, it's the speed of the wave.
This is also in the formula :
lambda=v/f which you should try memorise imo.
Once you've got the speed you can answer the questions.
The question didn't say anything about changing the wave media so I still don't understand where you think the contradiction arose. 
Primus2x
 Follow
 0 followers
 2 badges
 Send a private message to Primus2x
 Thread Starter
Offline2ReputationRep: Follow
 11
 25032013 11:09
(Original post by Joinedup)
f=50hz so in one second you get 50 complete wave cycles, peak and trough. The waves move away from the source at an unknown speed.
The distance between peaks (wavelength) is 0.2 meters.
The distance covered by one seconds worth of waves is the wavelength multiplied by the number of waves emitted in a second. I.e. At the instant you finish emitting the 50th peak, the first peak is 50*0.2 meters away.
It took one second to emit those 50 complete wave cycles.
Distance per second is a speed, it's the speed of the wave.
This is also in the formula :
lambda=v/f which you should try memorise imo.
Once you've got the speed you can answer the questions.
The question didn't say anything about changing the wave media so I still don't understand where you think the contradiction arose. 
 Follow
 12
 25032013 11:30
(Original post by Primus2x)
So I work backwards from what I thought? Find the speed first, then the distance then the number of waves?
Part a. you can just answer straight away without knowing the wavelength.
Fwiw old exam questions used to ask you for the answers in the 'wrong order' i.e. Intermediate result last, quite often. Otoh modern exam questions tend to ask you for the answers in the order in which you'd calculate them. Just something to bear in mind if you're practicing on old exam papers. 
RVNmax
 Follow
 15 followers
 18 badges
 Send a private message to RVNmax
 Study Helper
Offline18ReputationRep:Study Helper Follow
 13
 25032013 22:43
(Original post by Primus2x)
(1/50)/20=1/1000, a thousandth?
The wavelength is 20cm or 2*10^{1}m to find the distance travelled do I multiply the wavelength by the number of waves there are? So it's my answer to part a) * the wavelength
Speed is distance over time, so part b)/20
So this all depends on part a) being correct.
b)(Original post by Primus2x)
So I work backwards from what I thought? Find the speed first, then the distance then the number of waves?
c) I didn't want to give you the formula because I wanted you to look back at your notes/remember it/work it out looking at what you were given.
I think you won't have any problems on that now. If you do struggle, just keep at it for a while before you ask again. If you need confirming of final answers then quote me. 
Primus2x
 Follow
 0 followers
 2 badges
 Send a private message to Primus2x
 Thread Starter
Offline2ReputationRep: Follow
 14
 25032013 23:20
Right, I've worked backwards;
c)V=lamda*f=0.2*50=10ms^1
b)V=d/T=10=d/20, 20*10=d=200m
a)200/50=4 complete waves, still not sure on this part, frequency is not just the reciprocal of time period, its how many waves emitted in 1 unit time, so distance over frequency? I'd have thought that wavelength is involved. 200/0.2 wavelengths=1000 waves.Last edited by Primus2x; 25032013 at 23:42. 
Season One
 Follow
 0 followers
 0 badges
 Send a private message to Season One
Offline0ReputationRep: Follow
 15
 25032013 23:26
How far a wave has travelled and wavelength are independent. Wavelength is the distance from one peak of the wave to the other. However how far a wave has travelled can be worked out using a few equations, e.g wavelength= speed/frequency
Last edited by Season One; 26032013 at 21:20. 
 Follow
 16
 26032013 00:16
(Original post by Primus2x)
Right, I've worked backwards;
c)V=lamda*f=0.2*50=10ms^1
b)V=d/T=10=d/20, 20*10=d=200m
a)200/50=4 complete waves, still not sure on this part, frequency is not just the reciprocal of time period, its how many waves emitted in 1 unit time, so distance over frequency? I'd have thought that wavelength is involved. 200/0.2 wavelengths=1000 waves. 
RVNmax
 Follow
 15 followers
 18 badges
 Send a private message to RVNmax
 Study Helper
Offline18ReputationRep:Study Helper Follow
 17
 26032013 21:21
(Original post by Primus2x)
Right, I've worked backwards;
c)V=lamda*f=0.2*50=10ms^1
b)V=d/T=10=d/20, 20*10=d=200m
a)200/50=4 complete waves, still not sure on this part, frequency is not just the reciprocal of time period, its how many waves emitted in 1 unit time, so distance over frequency? I'd have thought that wavelength is involved. 200/0.2 wavelengths=1000 waves.
You don't need c or b for part a). It is very simple 
A source of waves has a frequency of vibration of 50Hz.
a) How many complete waves are emitted in 20s?
If you know how long one wave takes to pass a certain point, a.k.a. the Time Period, how many of those wave will pass in 20s. I would do 20s/(1/50Hz), yes that is the answer you originally got, which I never said was wrong.
Though the way you did it right at the end was also correct as total distance in 20s divided by length of each wave just says same thing. 
Primus2x
 Follow
 0 followers
 2 badges
 Send a private message to Primus2x
 Thread Starter
Offline2ReputationRep: Follow
 18
 30032013 00:01
Thanks, wont hear back from it until after Easter.
 Basic Waves help!
 How does a scanning tunnelling microscope work?
 Waves
 why does the speed of light change in different mediums?
 Extended Project for Physics
 UK astronomers plan to look for ETs.
 Anyone that does physics/chemistry, I got on confusing ...
 "If a tree falls in a forest and no one is around to hear it, does it ...
 Huygens Principle
 Why don't electrons fall into the nucleus?

University of Glasgow

University of Hertfordshire

University of Leeds

Physics with Professional Placement & Research Placement
University of Bath

Physics and Astronomy (Gateway MPhys)
University of St Andrews

University of Bath

University of Liverpool

Loughborough University

University of Surrey

Physics with Theoretical Physics
Imperial College
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.
 charco
 Mr M
 Changing Skies
 F1's Finest
 rayquaza17
 Notnek
 RDKGames
 davros
 Gingerbread101
 Kvothe the Arcane
 TeeEff
 The Empire Odyssey
 Protostar
 TheConfusedMedic
 nisha.sri
 claireestelle
 Doonesbury
 furryface12
 Amefish
 harryleavey
 Lemur14
 brainzistheword
 Rexar
 Sonechka
 TheAnxiousSloth
 EstelOfTheEyrie
 CoffeeAndPolitics
 an_atheist
 Labrador99
 EmilySarah00