One of the following statements is incorrect. Select it. a) If two or more waves

Question

One of the following statements is incorrect. Select it.

a) If two or more waves are passing through a point at the same time, the net displacement of the medium is equal to the sum of the displacements induced by the individual waves.

b) The longest possible wavelength of a standing wave on a string fixed at both ends is equal to the twice the length of the string.

c) Doubling the amplitude of a wave quadruples its intensity.

d) A pulse propagating down a taut string is reflected from the end of the string. The end of the string is fixed. The reflected pulse has the same sign as the incident pulse.

e) Doubling the length of a string fixed at both ends halves its fundamental harmonic frequency.

f) A standing wave on a string is the superposition of two waves of equal amplitude and frequency but traveling in opposite directions.

Explanation / Answer

(a)

correct because of superposition theorem

y = y1 + y2

(b)

correct because lamda = 2L for first harmonic, in the remaing harmonics wavelength is less than that of first harmonic

(c)

correct because I proprotional to A^2

I1= A1^2

I2 = A2^2

I2/I1 =(A2/A1)^2

I2 = I1 ( 2A1/A1)^2

= 4I1

(d)

incorrect  The reflected pulse does not have same sign as the incident pulse

(e)

f= v/2L

when lenght is doubled

f1 = v/ 2( 2L)

= f/2

correct

(f)

correct

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