CBSE 11th Standard Physics Subject Waves Ncert Exemplar 2 Mark Questions With Solution 2021
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CBSE 11th Standard Physics Subject Waves Ncert Exemplar 2 Mark Questions With Solution 2021
11th Standard CBSE
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Reg.No. :
Physics
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At what temperature (in 0C) Will be speed of sound air be 3 times its value at 00 C?
(a) -
A sitar wire is replaced by another wire of same length and material but of three times the earlier radius. If the tension in the wire remains the same, then by what factor will the frequency change?
(a) -
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 ± v t). Is the converse true? Examine if the following functions for y can possibly represent a travelling wave :
(i) (x - vt) 2
(ii) log [(x + vt)/x0]
(iii) 1/(x + vt)(a) -
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- vt or x + vt, i.e. y = f( x \(\pm \) vt ). Is the converse true?
(a) Examine if the following functions for Y can possibly represent a travelling wave
(b) Examine if the following functions for Y can possibly represent a travelling wave (x - vt)2(a)
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CBSE 11th Standard Physics Subject Waves Ncert Exemplar 2 Mark Questions With Solution 2021 Answer Keys
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We know that, speed, \(v\infty \sqrt { T } \)
By formula v = \(\frac { xRT }{ p } \)
Where T is in kelvin
\(\frac { v_{ t } }{ v_{ 0 } } =\sqrt { \frac { 273+t }{ 273+0 } } =3\)
\(\\ \Rightarrow \frac { 273+t }{ 273 } =9\Rightarrow \ t=9\times 273-273=2184^{ 0 }C\) -
\({ v }_{ 1 }=\frac { 1 }{ { l }_{ 1 }{ D }_{ 1 } } \sqrt { \frac { { T }_{ 1 } }{ { \pi \rho }_{ 1 } } } \)
Where, D = diameter of wire
\( { v }_{ 2 }=\frac { 1 }{ { l }_{ 2 }{ D }_{ 2 } } \sqrt { \frac { { T }_{ 2 } }{ { \pi \rho }_{ 2 } } } \)
\( { l }_{ 1 }={ l }_{ 2 },\ { \rho }_{ 2 }={ \rho }_{ 1 }\)
\( { T }_{ 2 }={ T }_{ 1 },\ { D }_{ 2 }={ 3D }_{ 1 }\)
\(\\ \Rightarrow { V }_{ 2 }=\frac { { V }_{ 1 } }{ 3 } \)
New frequency is \(\frac { 1 }{ 3 } \) rd of the original frequency. -
Conceptual question based on fundamentals of characteristics of travelling wave.
The converse is not true means if the function can be represented in the form y = f( x \(\pm \) vt ), it does not necessarily express a travelling wave. As the essential condition for a travelling wave is that the vibrating particle must have finite displacement value for all x and t.
(i) For x = 0
If t \(\rightarrow \)0, then (x - vt)2\(\rightarrow \)0 which is finite, hence, it is a wave as it passes the two tests.
(ii) log \(\left( \frac { x+vt }{ x_{ 0 } } \right)\)
l\( \\ At\ x=0\ and\ t=0,\)
\( f(x,t)=log\left( \frac { 0+0 }{ x_{ 0 } } \right) \)
= log 0 \(\rightarrow\) not defined
Hence, it is not a wave.
(iii) \(\frac { 1 }{ x+vt } \)
\( \\ For\ x=0,\ t=0,\ f(x)\rightarrow \infty\)
Though the function is of (x\(\pm\) vt) type still at x = 0, it is infinite, hence, it is not a wave. -
(a) Conceptual question based on fundamentals of characteristics of travelling wave.
The converse is not true means if the function can be represented in the form y = f( x \(\pm \) vt ), it does not necessarily express a travelling wave. As the essential condition for a travelling wave is that the vibrating particle must have finite displacement value for all x and t.
\(\frac { 1 }{ x+vt } \)
\(\\ For\ x=0,\ t=0,\ f(x)\rightarrow \infty \)
Though the function is of (x±vt) type still at x=0, it is infinite, hence, it is not a wave.
(b) Conceptual question based on fundamentals of characteristics of travelling wave.
The converse is not true means if the function can be represented in the form y = f( x ± vt ), it does not necessarily express a travelling wave. As the essential condition for a travelling wave is that the vibrating particle must have finite displacement value for all x and t.
For x = 0,
If t →0, then (x-vt)2→0 which is finite, hence, it is a wave as it passes the two tests.
