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NCERT/CBSE PHYSICS CLASS 11 textbook http://www.TutorBreeze.com Answers to NCERT/CBSE PHYSICS Class 11(Class XI)textbook CHAPTER Fifteen
WAVES EXERCISES
15.12 (i) For the wave on a string described in Exercise 15.11, do all the points on the string oscillate with the same (a) frequency, (b) phase, (c) amplitude? Explain your answers. (ii) What is the amplitude of a point 0.375 m away from one end? Q. 15.12
By looking on the general equation of the stationary wave:‐
⎛ 2π ⎞ y ( x1t ) = 0.06 sin ⎜ x ⎟ cos (120πt ) ⎝ 3 ⎠
We see that ‐‐
‐‐frequency remain same for every n, thus frequency of all particles is same except nodes.
‐‐ Same as frequency.
‐‐ amplitude changes for each point as its value is different for different x.
(ii)
⎛ 2π ⎞ x ⎟ cos (120πt ) equation of wave ⇒ y ( x1t ) = 0.06 sin ⎜ ⎝ 3 ⎠
⎛ 2π ⎞ x⎟ Amplitude of wave = 0.06 sin ⎜ ⎝ 3 ⎠
⎛ 2π ⎞ ⎛π⎞ A = 0.06 sin ⎜ × 0.375 ⎟ = 0.06 sin ⎜ ⎟ = 0.042m ⎝ 3 ⎠ ⎝4⎠
x = 0.375
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