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Question 11 Mark
You have learnt that a travelling wave in one dimension is represented by a function $y=f(x, t)$ where $x$ and $t$ must appear in the combination $x-v t$ or $x+v t$, i.e. $y=f(x \pm v t)$. Is the converse true? Examine if the following functions for $y$ can possibly represent a travelling wave :
(a) $(x-v t)^2$$\quad$$\quad$(b) $\log \frac{(x+v t)}{x_0}$$\quad$$\quad$(c) $\frac{1}{(x+v t)}$
Answer
No, the converse is not true. It is basic restriction to represent progressive wave is that X and t. The value of the wave function should be limited for all values. None of the given functions satisfy this condition. For this reason these function not exibit progressive waves.
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Question 21 Mark
Explain why the shape of a pulse gets distorted during propagation in a dispersive medium.
Answer
In a dispersive medium, waves of different wavelength travel with different speed in different direction. Therefore, the shape of the pulse get distorted, that is no plane wave in a non-dispersive medium and a plane wave in dispersive medium.
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Question 31 Mark
Explain why solids can support both longitudinal and transverse waves, but only longitudinal waves can propagate in gases, and
Answer
This is because solids have both volume elasticity and shape elasticity. Therefore both transverse and longitudinal waves can pass through them. On the other hand gases have only volume elasticity of shape and no shear elasticity hence only longitudinal waves can propagate in gases.
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Question 41 Mark
Explain why a violin note and sitar note may have the same frequency, yet we can distinguish between the two notes.
Answer
Even though the frequencies of the notes of violin and gitar are same we can differentiate between the notes produced by them since the number of overtones in the sound produced by a violoin or gitar is different. We can differentiate between the notes produced by them.
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Question 61 Mark
An observer on the seashore sees waves reaching the shore, what type of waves does the observer see? Why?
Answer
Eliptic waves, while transverse wave occurs at the surface of water, but longitudinal wave occurs just below the water surface. Hence the resulting waves will be eliptical
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Question 71 Mark
Why does light come before sound in the under storm?
Answer
Speed of light is greater than speed of sound.
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Question 91 Mark
What will effect on wave length and frequency when we increase diameter of resonance tube?
Answer
Wave length will increase and frequency will decrease due to decreasing diameter.
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Question 101 Mark
Between the first and fifth nodes is 40 cm then find wavelength of wave?
Answer
We know that distance between two consecutive nodes is $\frac{\lambda}{2}$.
So first and fifth between distance $\frac{4 \times \lambda}{2}$ Means it is equal to $2 \lambda$.
$\therefore \quad 2 \lambda=40 \quad \therefore \lambda=\frac{40}{2}=20 cm$
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Question 111 Mark
In which of the gases, liquids or solids is the speed of sound heighest?
Answer
The velocity of sound is maximum in solids.
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Question 121 Mark
A tunning frok produce resonance in a closed tube, but it can't produce resonance in an open tube of the same length. why?
Answer
In same length's open or close tube because the fundamental frequency of resonance is different.
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Question 141 Mark
Why is a woman's voice sweeter than a man?
Answer
Because the frequency of a woman's voice is higher than that of a man.
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Question 151 Mark
What is the nature of ultrasonic waves and frequency?
Answer
Ultrasonic waves are longitudinal waves and frequency is 20000 Hz or greater.
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Question 161 Mark
Relation between phase difference and path difference.
Answer
Phase difference $=\frac{2 \pi}{\lambda} \times$ path difference
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Question 171 Mark
The weight hanging from the sonometer wire is increased by a factor of weight. Will the frequencies of the wire increase by exactly a factor of two? Explain your answer.
Answer
No, there will be a very slight increase in length of the wire, so the frequency will be slightly less by a factor of two.
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Question 211 Mark
You can create waves in any pond by throughing any stone then source of energy of waves.
Answer
Stones kinetic energy is source of wave energy.
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Question 221 Mark
What is the reason that generated sound in air can't be heared or less heares in water to the observer?
Answer
Because at surface of water interferance is significantly greater then reflection
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Question 251 Mark
When stationary waves can be generated?
Answer
When there are two waves with different- different amplitude
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Question 271 Mark
Tone of open pipe is softer then tune of close pipe, why?
Answer
Close pipe have only odd harmonic while open pipe have both (odd and even) harmonic. Generated harmonic in open pipe is greater then generated harmonic in close pipe. So it has soft tone.
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Question 311 Mark
What is the formula of velocity of sound in gases according to Laplace's correction?
Answer
$\text v =\sqrt{\frac{\gamma P }{d}}$
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Question 321 Mark
Relation between phase difference and path difference.
Answer
$\Delta \phi=\frac{2 \pi}{\lambda} \Delta x$
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Question 331 Mark
The wave equation is $y=5 \sin 2 \pi\left(\frac{t}{0.02}-\frac{x}{20}\right)$
Find the frequency and time periodic.
Answer
$y=5 \sin \left(\frac{2 \pi t}{0.02}-\frac{2 \pi x}{20}\right)$
It is clear from equation
$\omega t=\frac{2 \pi}{0.02} t$
$\therefore \quad \omega=\frac{2 \pi}{0.02}$
$\frac{2 \pi}{T}=\frac{2 \pi}{0.02} \quad \therefore T=0.02$ second
Frequency $\quad n=\frac{1}{T}=\frac{1}{0.02}=\frac{100}{2}=50 Hz$
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1 Marks Question - Physics STD 11 Science Questions - Vidyadip