1 Marks Question

Question 1011 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:
$\text{y}=2\cos(3\text{x})\sin(10\text{t})$

Answer

The given equation represents a stationary wave because the harmonic terms kx and ωt appear separately in the equation.

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Question 1021 Mark

Is it possible to have interference between the waves produced by two violins? Why?

Answer

No. This is because the sounds produced will not have a constant phase difference.

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Question 1031 Mark

Answer

The given equation does not contain any harmonic term. Therefore, it does not represent either a travelling wave or a stationary wave.

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Question 1041 Mark

An open pipe makes a good musical instrument, in comparison to a closed pipe. Why?

Answer

In open pipe, all harmonics are possible, while in a closed pipe, only odd harmonics are possible.

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Question 1051 Mark

What determines the type of wave motion in a medium?

Answer

Type of wave motion is determined by:

Nature of the medium.
Mode of excitation of wave motion.

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Question 1061 Mark

What sort of waves are formed in a sitar wire when it is once plucked in the middle and then released?

Answer

Transverse stationary waves are formed in the sitar wire.

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Question 1071 Mark

What is the relation between path difference and phase difference?

Answer

Phase difference $=\frac{2\pi}{\lambda}\times\text{path difference.}$

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Question 1081 Mark

Where does the pressure of larger magnitude exist at nodes or at antinodes?

Answer

Pressure is maximum at points of minimum displacement. So, it is maximum at nodes.

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Question 1091 Mark

Two sounds of very close frequencies, say 256Hz and 260Hz are produced simultaneously. What is the frequency of resultant sound and also write the number of beats heard in one second?

Answer

$\text { No. of beats } n=n_2-n_1$
$=260-256$
$=4$
Frequency of resultant sound is the average of the two frequencies 258 Hz .

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Question 1101 Mark

What is the effect on the velocity of waves in a string if only $\frac{1}{4}\text{th}$ of the original length is used with the same tension?

Answer

Since $\frac{\text{m}}{\text{l}}$ is not altered and tension is same, velocity will remain the same.

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Question 1111 Mark

Is Newton's law of motion applicable for material waves? Is this applicable for electromagnetic waves?

Answer

Newton's laws of motion are applicable for material waves but not applicable for electromagnetic waves.

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Question 1121 Mark

Two sitar strings A and B playing the note ‘Dha’ are slightly out of tune and produce beats of frequency 5 Hz. The tension of the string B is slightly increased and the beat frequency is found to decrease to 3 Hz. What is the original frequency of B if the frequency of A is 427 Hz ?

Answer

Increase in the tension of a string increases its frequency. If the original frequency of $B \left(v_B\right)$ were greater than that of $A \left(v_A\right)$, further increase in $v_B$ should have resulted in an increase in the beat frequency. But the beat frequency is found to decrease. This shows that $v_B<v_A$. Since $v_A-v_B=5 Hz$, and $v_A=427 Hz$, we get $v_B=422 Hz$.

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Question 1131 Mark

A steel wire $0.72 m$ long has a mass of $5.0 \times 10^{-3} kg$. If the wire is under a tension of $60 N$, what is the speed of transverse waves on the wire?

Answer

Mass per unit length of the wire,
$
\begin{aligned}
\mu & =\frac{5.0 \times 10^{-3} kg }{0.72 m } \\
& =6.9 \times 10^{-3} kg m ^{-1}
\end{aligned}
$
Tension, $T=60 N$
The speed of wave on the wire is given by
$
v=\sqrt{\frac{T}{\mu}}=\sqrt{\frac{60 N }{6.9 \times 10^{-3} kg m ^{-1}}}=93 m s ^{-1}
$

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Question 1141 Mark

Given below are some examples of wave motion. State in each case if the wave motion is transverse, longitudinal or a combination of both:
(a) Motion of a kink in a longitudinal spring produced by displacing one end of the spring sideways.
(b) Waves produced in a cylinder containing a liquid by moving its piston back and forth.
(c) Waves produced by a motorboat sailing in water.
(d) Ultrasonic waves in air produced by a vibrating quartz crystal.

Answer

(a) Transverse and longitudinal
(b) Longitudinal
(c) Transverse and longitudinal
(d) Longitudinal

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Physics 1 Marks Question