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Question : 10
Total: 27
For the travelling harmonic wave
y(x,t)=2.0cos2π(10t0.0080x+0.35)
Where x and y are in cm and t in s. Calculate the phase difference between oscillatory motion of two points separated by a distance of
(a) 4 m
(b) 0.5 m
(c)
λ
2

(d)
3λ
4
Solution:  
Given equation of a travelling harmonic wave is
y(x,t)=2.0cos2π(10t0.0080x+0.35) ...(i)
The standard equation of a travelling harmonic wave is
y(x,t)=Acos[
2π
T
t
2π
λ
x
+ϕ0
]
...(ii)
Comparing equation(i) and (ii), we get
2π
λ
=2π×0.0080cm1
...(iii)
2π
T
=2π×10
and ϕ0=0.35
We know that,
phase difference =
2π
λ
×
path difference ...(iv)
(a) When path difference = 4m = 400 cm, then from (iv)
phasedifference =
2π
λ
×400
=6.4π rad
(b) When path difference = 0.5 m = 50 cm, then
phase difference =2π×0.0080×50 =0.8π rad
(c) When path difference =
λ
2
, then
phase difference =
2π
λ
×
λ
2
=π
rad
(d)When path difference =
3π
4

phase difference =
2π
λ
×
3λ
4
=
3π
2
rad =(π+
π
2
)

∴ effective phase difference =
π
2
rad
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