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Physics 1 Marks Question

Waves · Rajasthan Board (RBSE) STD 11 Science (Rajasthan - English Medium). 114 questions.

Questions · Page 2 of 3

1 Marks Question

Question 511 Mark
For the travelling harmonic wave
$\text{y}(\text{x, t})=2.0\cos2\pi(10\text{t}-0.0080\text{x}+0.35)$
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
0.5m,
Answer
Equation for a travelling harmonic wave is given as:
$\text{y}(\text{x, t})=2.0\cos2\pi(10\text{t}-0.0080\text{x}+0.35)$
$=2.0\cos(20\pi\text{t}-0.016\pi\text{x}+0.70\pi)$
Where,
Propagation constant, $\text{k}=0.0160\pi$
Amplitude, a = 2cm
Angular frequency, $\omega=20\pi\text{ rad/s}$
Phase difference is given by the relation:
$\phi=\text{kx}=\frac{2\pi}{\lambda}$
For x = 0.5m = 50cm
$\phi=0.016\pi\times50=0.8\pi\text{ rad}$
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Question 521 Mark
An observer is stationed at x = 10cm. When a train moves in the y-axis with a velocity 10m/s, what is the apparent frequency?
Answer
There is no Doppler shift in perpendicular direction, so no apparent frequency.
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Question 541 Mark
In an open organ pipe, third harmonic is 450Hz. What is the frequency of fifth harmonic?
Answer
$\because \text{v}_3=3\text{v}_1$
$\text{v}_3=450\text{Hz}$
$\therefore 450=3\text{v}_1$
$\Rightarrow\text{v}_1=150\text{Hz}$
Fifth harmonic,
$\text{v}_5=5\text{v}_1$
$=5\times150$
$\text{v}_5=750\text{Hz}$
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Question 551 Mark
If oil of density higher than density of water is used in a resonance tube, how will the frequency change?
Answer
The frequency will not change. Because frequency depends on length of air column above the liquid surface in the tube.
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Question 561 Mark
What is the difference between a tone and a note?
Answer
Note is sound of particular frequency, while tone is of a particular intensity.
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Question 571 Mark
The ratio of amplitude of two waves is 2 : 3. What is the ratio of intensities of these waves?
Answer
$\frac{\text{I}_1}{\text{I}_2}=\frac{\text{a}^2}{\text{b}^2}=\frac{2^2}{3^2}$
$=\frac{4}{9}$
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Question 591 Mark
If tension of a wire is increased to four times, how is the wave speed changed?
Answer
As $v\propto\sqrt{\text{T}},$ therefore, wave speed becomes twice.
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Question 601 Mark
Periodic rise and fall of intensity of sound when two sound waves moving in same direction, having same amplitude but differ in frequency by less than 10 is known as ________.
Answer
Periodic rise and fall of intensity of sound when two sound waves moving in same direction, having same amplitude but differ in frequency by less than 10 is known as beat.
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Question 611 Mark
What causes the rolling sound of thunder?
Answer
The rolling sound of thunder is due to multiple reflection of sound of lightning.
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Question 621 Mark
How many beats are formed when two sources vibrate in unison?
Answer
No beats are formed, since $\mathrm{v}_{\mathrm{b}}=\mathrm{V}_1-\mathrm{V}_2$.
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Question 631 Mark
What will be the speed of sound in a perfectly rigid rod?
Answer
The speed of sound in a perfectly rigid rod will be infinite.
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Question 641 Mark
The pattern of standing waves formed on a stretched string at two instants of time are shown in The velocity of two waves superimposing to form stationary waves is $360\ ms^{–1}$ and their frequencies are $256\ Hz$
  1. Calculate the time at which the second curve is plotted.
  2. Mark nodes and antinodes on the curve.
  3. Calculate the distance between $A′$ and $C′.$
Answer
Given frequency of the wave $v = 256Hz$
$\therefore\text{T}=\frac{1}{\text{v}}=\frac{1}{256}$ second $= 0.00390$
$\text{T}=3.9\times10^{-3}$ seconds.
$(a)$ In stationary wave a particle passes though it's mean position after ever $\frac{\text{T}}{4}$ time
$\therefore$ in II nd curve displacement of all medium particle, are zero so
$\text{t}=\frac{\text{T}}{4}=\frac{3.9\times10^{-3}}{4}=.975\times10^{-3}\sec$
$\text{t}=9.8\times10^{-4}$ secound.
$(b)$ Point does not vibrate i.t., their displacement is zero always so nodes $\text{A, B, C, D}$ and $E$. the point $A\ '$ and $C\ '$ are at maximam displacement so there are anti$-$nodes at $A\ '$ and $C\ '.$
Between $A\ '$ and $C\ '=\lambda=\frac{\text{v}}{\text{V}}=\frac{360}{256}=\frac{90}{64}=1.41\text{m}.$
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Question 651 Mark
Fundamental frequency of oscillation of a close pipe is 400Hz. What will be the fundamental frequency of oscillation of an open pipe of same length?
Answer
800Hz.
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Question 661 Mark
State the factors on which the speed of a wave travelling along a stretched ideal string depends.
Answer
Speed depends on Tension and Mass per unit length.
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Question 671 Mark
When a vibrating tunning fork is moved speedily towards a wall, beats are heard. Why?
Answer
This is due to the difference in the frequency of the incident wave and the apparent frequency of the reflected wave.
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Question 681 Mark
For the travelling harmonic wave
$\text{y}(\text{x, t})=2.0\cos2\pi(10\text{t}-0.0080\text{x}+0.35)$
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
4m.
Answer
Equation for a travelling harmonic wave is given as:
$\text{y}(\text{x, t})=2.0\cos2\pi(10\text{t}-0.0080\text{x}+0.35)$
$=2.0\cos(20\pi\text{t}-0.016\pi\text{x}+0.70\pi)$
Where,
Propagation constant, $\text{k}=0.0160\pi$
Amplitude, a = 2cm
Angular frequency, $\omega=20\pi\text{ rad/s}$
Phase difference is given by the relation:
$\phi=\text{kx}=\frac{2\pi}{\lambda}$
For x = 4 m = 400cm
$\phi=0.016\pi\times400=6.4\pi\text{ rad}$
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Question 711 Mark
Given below are some functions of x and t to represent the displacement (transverse or longitudinal) of an elastic wave. State which of these represent (i) a travelling wave, (ii) a stationary wave or (iii) none at all:
$\text{y}=\cos\text{x}\sin\text{t}+\cos2\text{x}\sin2\text{t}$
Answer
The given equation represents a stationary wave because the harmonic terms kx and $\omega\text{t}$ appear separately in the equation. This equation actually represents the superposition of two stationary waves.
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Question 721 Mark
What is the phase difference between two successive crests in a transverse wave?
Answer
Phase difference between two successive crests in a transverse wave is $2\pi$ rad.
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Question 731 Mark
What type of graph you expect between speed of sound through a gas and pressure of gas?
Answer
The graph will be straight line parallel to pressure axis.
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Question 741 Mark
A pipe 20cm long is closed at one end. Which harmonic mode of the pipe is resonantly excited by a source of 1237.5Hz?(sound velocity in air $= 330ms^{–1}$)
Answer
Length of pipe, $\text{l}=20\text{cm}=20\times10^{-2}\text{m}$
Fundamental frequency of closed organ pipe
$\text{f}_0=\frac{\text{v}}{4\text{}L}=\frac{330}{4\times20\times10^{-2}}=412.5\text{Hz}$
$\frac{\text{f given}}{\text{f}_0}=\frac{1237.5}{412.5}=3$
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Question 751 Mark
How can we distinguish between a violin and a sitar note?
Answer
The quality of sound and overtones produced will be different. So, we can identify.
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Question 771 Mark
What is the nature of waves produced in a tuning fork?
Answer
In tuning forks, standing waves are produced with antinode at the free ends.
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Question 781 Mark
Name the waves which do not require any material medium for their propagation.
Answer
Non-mechanical or electromagnetic waves.
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Question 791 Mark
When will Doppler effect in sound be symmetrical?
Answer
When the velocity of the source or observer is very much less than the velocity of sound.
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Question 801 Mark
For the harmonic travelling wave $\text{y}=2\cos2\pi(10\text{t}-0.0080\text{x}+3.5)$ where x and y are in cm and t is second. What is the phase difference between the oscillatory motion at two points separated by a distance of:
$\frac{3\lambda}{4}$(at a given instant of time)
Answer
$\text{y}=2\cos2\pi(10\text{t}-0.0080\text{x+3.5})$ $\text{y}=2\cos(20\pi\text{t}-0.0016\pi\text{x}+7.0\pi)$ Wave is propagated in $+\text{x}$ direction because $\omega\text{t}$ and kx are in with opposite sign standard equation $\text{y}=\text{a}\cos(\omega\text{t}-\text{kx}+\phi)$ a = 2, $\omega=20\pi,\ \text{k}=0.016\pi$ and $\phi=7\pi$$\Delta\phi=\frac{2\pi}{\lambda}\text{p}=\frac{2\pi}{\lambda}\times\frac{3\pi}{4}=\frac{3}{2}\pi\ \text{radian}$
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Question 811 Mark
At the same temperature and pressure, the densities of two diatomic gases are d, and d. What is the ratio of the speeds of sound in these gases?
Answer
$\frac{v_1}{v_2}=\sqrt{\frac{\text{d}_2}{\text{d}_1}}$
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Question 831 Mark
A transverse harmonic wave on a string is described by
$\text{y}(\text{x, t})=3.0\sin\big(36\text{t}+0.018\text{x}+\frac{\pi}{4}\big)$
where x and y are in cm and t in s. The positive direction of x is from left to right.
What is the initial phase at the origin?
Answer
$\frac{\pi}{4}$
Explanation:
Given,
$\text{y}(\text{x, t})=3\sin\big(36\text{t}+0.018\text{x}+\frac{\pi}{4}\big)$
Initial phase at the origi $=\frac{\pi}{4}$
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Question 841 Mark
Why should the difference between the frequencies be less than 10 to produce beats?
Answer
Human ear cannot identify any change in intensity is less than $\Big(\frac{1}{10}\Big)\text{th}$ of a second. So, difference should be less than 10.
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Question 851 Mark
Is the phenomenon of beats observable in case of two light waves of nearly equal frequencies?
Answer
No, this is because phase difference due to two independent light sources changes rapidly and randomly at a given position.
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Question 861 Mark
Name the factors affecting the velocity of sound in a medium.
Answer
Temperature, density and ratio $\gamma$ affect the velocity of sound in a medium.
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Question 871 Mark
Give one similarity and one difference between a S.H.M. and a Wave.
Answer
Similarity- Periodic nature.
Difference- Wave is a function of position and time, while a SHM is a function of time only.
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Question 881 Mark
Velocity of sound in air at N.T.P. is 332m/s. What will be the velocity, when pressure is doubled and temperature is kept constant?
Answer
v = 332m/s, as there is no effect of change in pressure when temperature remains constant.
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Question 891 Mark
In a longitudinal wave, what is the distance between a compression and its nearest rarefraction?
Answer
$\frac{\lambda}{2}.$
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Question 901 Mark
Two sound sources produce 12 beats in 4 seconds. By how much do that frequencies differ?
Answer
Beat frequency $=\frac{12}{4}=3\text{beats/ sec}.$
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Question 911 Mark
_______ waves do not transfer any energy and momentum in the material medium.
Answer
Standing waves do not transfer any energy and momentum in the material medium.
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Question 921 Mark
When a source moves at a speed greater than that of sound, will Doppler formula hold? What will happen?
Answer
No, as it is valid only when $v_s<v$. When $v_s>v$, shock waves are produced.
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Question 931 Mark
In the given progressive wave $​​​​\text{y}=5\sin(100\pi\text{t+0.4x})$ where y and x are in m, t is in s. What is the:
Amplitude
Answer
Standard form of progressive wave travelling in $+\text{x}$ direction (kx and $\omega\text{}t$ have opposite sign is given)
Eqn. is $\text{y}=\text{a}\sin(\omega\text{t}-\text{kx}+\phi)$
$\text{y}=5\sin(100\pi\text{t}-0.4\pi\text{t}+0)$
Amplitude $\text{a}=5\text{m}$
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Question 951 Mark
State the factors on which the speed of a wave travelling along a stretched ideal string depends.
Answer
The speed of a wave travelling along a streched ideal string,
$\text{v}=\sqrt{\frac{\text{T}}{\text{m}}}$
where, $T$ is the tension in the string and m is mass per unit length of the string.
Hence, it depends on two factors:
  1. Tension in the string.
  2. Mass per unit length.
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Question 961 Mark
What is reverberation?
Answer
The persistence of audible sound after the source has ceased to produce the sound is called reverberation.
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Question 971 Mark
For the travelling harmonic wave
$\text{y}(\text{x, t})=2.0\cos2\pi(10\text{t}-0.0080\text{x}+0.35)$
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
$\frac{\lambda}{2},$
Answer
Equation for a travelling harmonic wave is given as:
$\text{y}(\text{x, t})=2.0\cos2\pi(10\text{t}-0.0080\text{x}+0.35)$
$=2.0\cos(20\pi\text{t}-0.016\pi\text{x}+0.70\pi)$
Where,
Propagation constant, $\text{k}=0.0160\pi$
Amplitude, a = 2cm
Angular frequency, $\omega=20\pi\text{ rad/s}$
Phase difference is given by the relation:
$\phi=\text{kx}=\frac{2\pi}{\lambda}$
For $\text{x}=\frac{\lambda}{2}$
$\phi=\frac{2\pi}{\lambda}\times\frac{\lambda}{2}=\pi\text{ rad}$
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Question 981 Mark
Why is sound heard more intense in carbon dioxide in comparison to air?
Answer
The intensity of sound increases with increase in density of the medium.
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Question 991 Mark
Given below are some functions of x and t to represent the displacement (transverse or longitudinal) of an elastic wave. State which of these represent (i) a travelling wave, (ii) a stationary wave or (iii) none at all:
$\text{y}=3\sin(5\text{x}-0.5\text{t})+4\cos(5\text{x}-0.5\text{t})$
Answer
The given equation represents a travelling wave as the harmonic terms kx and ωt are in the combination of $\text{kx}-\omega\text{t}.$
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Question 1001 Mark
If radius of a stretched wire is reduced to half, how is the wave speed affected?
Answer
As $v\propto\frac{1}{\sqrt{\text{r}}},$ therefore, wave speed becomes twice.
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1 Marks Question - Page 2 - Physics STD 11 Science Questions - Vidyadip