575 - Physics Questions Answers
two sound waves having intensities 4 unit and 9 unit coming from two coherent sources arrive at a point along the same line simultaneously in same phase. resultant intensity at the point will be
Use the formule I = I1 + I2 + 2 √I1 √I2 cosθ
here θ = 0
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two sound sources of intensity I and 4I are used in an interference experiment. find the intensity at points where the waves from the two sources are superimposed with a phase difference of
(1) zero
(2) π/2
93)π
Use the formule I = I1 + I2 + 2 √I1 √I2 cosθ
here θ = 0
in a large room, a person receives direct sound wave from a source 120m away from him. he also receives wave from the same source which reaches him after being reflected from 25m high ceiling at apoint midway between them. the two waves interfere constructively for wavelength of
(1) 20, 20/3, 4
(2) 10, 5, 3.33
(3) 10, 20, 30
(4) 15, 25, 35
path difference between two waves one coming directly (path length = 120 m) and other coming after reflection (path length = 130), you can get this by geometry
so path difference = 10 m
for constructive interference path difference should be a multiple of wavelength so (2) is answer
a source of sound and an observer are moving with velocities v = (2i + 4j)m/s and v = (6i - 3j)m/s. if frequency of source is 400 Hz, then frequency observed by observer will be
dot product of the two velocities given = 0, means observer and source are moving perpendicularly, so observer will observe the original frequency.
two waves are represented by y = Acosωt and y = Asin(ωt - π/6), superimpose on each other. the amplitude of the rsultant wave is
first convert cos into sin then calculate phase difference, its value will be π/2 + π/6 = 2π/3
now use the formula for resultant amplitude
which of the following phenomenon cannot be observed with sound waves?
(1) diffraction
(2) polarisation
(3) reflection
(4) interference
polarisation
a source of sound of frequency f emits sound wave with speed v is at rest. if an observer is moving towards source with speed Vo(V not), then wavelength of sound waves observed by the observer will be
(1) v/f
(2) (v - Vo)/f
(3) [v(v - Vo)]/[f(v + Vo)]
(4) [v(v + Vo)]/[f(v - Vo)]
since velocity and frequency are changing proportionally so wavelength will be constant = v/f
a sonometer wire supports a 4kg load and vibrates in fundamental mode with a tuning fork of frequency 416 Hz. the length of the wire between the bridges is now doubled. in order to maintain fundamental mode the load should be changed to
for sonometer wire
in fundamental mode l = λ/2 = v/2f here l, λ and f are length , wavelength and frequency respectively
now v = √(T/µ) here T and µ are tension and mass per unit length
so finally we will get l = √(T/µ)/2f
make two equations by using this formula and given conditions
in the two equations f and µ will be same
in a stationery wave, there is no energy current, but there is energy density. (TRUE/FALSE)
TRUE
at STP, the speed of sound in hydrogen is 1324ms‾¹ then the spped of sound in air (at STP) is
formula for speed of sound is v = √(γRT/M)
you have to form two equations for the two mediums, for both the mediums γ will be same because Hydrogen and Air both are diatomic gases, T will also be same for both the cases are taken in STP, only M will be different