Stationary waves

y=Acos(wt-kx)
y=Asin(wt+kx)

Can they form stationary waves? I say yes. My book says no. Need a confirmation.

22 Answers

1
swordfish ·

@qwerty

I did not understand you completely.
Can you find the direction of any one wave by using that method so that it will be more clear?

1
kunl ·

yup i m sorry swordy i misguided u in beginning actually i did not read waves till then properly now i m pretty sure they will form![1]

6
AKHIL ·

they wud form a stationary wave.......

71
Vivek @ Born this Way ·

Atleast post your final answer.

1
swordfish ·

Thanks!!
That helped.

23
qwerty ·

wave shape isnt changing with time .
what you are talking is about ∂f/∂t , i.e assuming x =constant, i.e you are talking for a particular x . If you fix x, then f represents diplacement of the element at x as a function of time .

1
swordfish ·

Btw, df/dt will give you the rate of change of y-co-ordinate of a point on the wave. In a transverse wave every point performs S.H.M. Why will it be 0?

1
swordfish ·

hmm....dx/dt is coming to be opposite in sign in two cases. So my book is wrong right?

23
qwerty ·

i will again say the same thing , you can find the direction

1
swordfish ·

lol.....read my post again. I am asking you to find out the direction of any one wave

23
qwerty ·

yes you can find the direction .

1
kunl ·

@talwarmachhli
just now ur friend jeemacchi came and told me that book is correct!

23
qwerty ·

if f(x,t) is the wave shape , then assuming that it doesnt change, df/dt =df/dx = 0

from either of the two you will get v = dx/dt or v=-dx/dt . That way you can decide the direction

11
jeetopper jee ·

it clearly represents the standing wave for any wave torepresent a standing wave there shoyld exist fixed points at a given time t at different cordinates this is clearly possible if you sole the cos term.

71
Vivek @ Born this Way ·

You mean there shouldn't be any constant (eg. Î /4) too ?

1
samagra Kr ·

combining the 2 eqs ,i m getting y=2Asin(π/4 +ωt)cos(kx-π/4) ;

To represent a standing wave the eq must be of the form ....
y=2Asin(ωt)cos(kx)

so it will not form a stationary wave

1
Vinay Arya ·

Swordifsh,the waves are of same amplitude,frequency and they are moving in the opposite directions.You can visualise that when they will collide then what will happen.

1
swordfish ·

y=Asin(wt-kx)
y=-Asin(kx-wt)

You tell me Akhil....are they along the same direction or opposite?

6
AKHIL ·

the direcn is decided by the term kx.

1
swordfish ·

which way then? be more clear.

1
kunl ·

its not that way swordy!

1
swordfish ·

we can write first wave as y=Asin(90-wt+kx)
Now is the direction of a wave decided by the sign of wt or kx ?

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