Download App

Wave Optics — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsWave Optics3 Marks
Question
Answer the following question:
Two students are separated by a 7 m partition wall in a room 10 m high. If both light and sound waves can bend around obstacles, how is it that the students are unable to see each other even though they can converse easily.
✓

Answer

The size of the obstacle or aperture should be comparable to the wavelength for diffraction of waves by obstacles, through a large angle.
This follows from $\text{sin}\theta=\frac{\lambda}{\text{a}}.$
For light waves,
Wavelength, $\lambda=10^{-7} \text{m and},$
Size of the wall, a = 10 m
$\therefore\ \text{sin}\theta=\frac{10^{-7}}{10}=10^{-8}$
This implies, $\theta\ \rightarrow\ 0$
That is, light goes almost unbent and hence, the students are unable to see each other.
For sound waves,
Frequency, $\nu$ = 1000 Hz
$\text{i.e}\ \frac{\text{c}}{\nu}=\frac{330}{1000}=0.33\ \text{m}$
$\therefore\ \text{sin}\theta=\frac{\lambda}{\text{a}}=\frac{0.33}{10}=0.033\ \text{m}$
Here, $\theta$ has a definite value and the waves will bend around the partition. Hence, students can converse easily.

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "3 Marks Question" from Wave Optics→Wave Optics — all question types→Physics STD 12 Science question papers→Rajasthan Board STD 12 Science question papers→Rajasthan Board question paper generator→

Similar questions

A cubical box of volume $216\ cm^3$ is made up of $0.1\ cm$ thick wood. The inside is heated electrically by a $100W$ heater. It is found that the temperature difference between the inside and the outside surface is $5^\circ C$ in steady state. Assuming that the entire electrical energy spent appears as heat, find the thermal conductivity of the material of the box.
→
What is the kinetic energy of an electron in electronvolts with mass equal to double its rest mass?
→
Write the working of transformer.
###
Derive the relation $\frac{v_s}{v_p}=\frac{ N _s}{ N _p}$ for an ideal transformer and mention corresponding assumptions.
→
  1. For a glass prism $(\mu =\sqrt{3} )$ the angle of minimum deviation is equal to the angle of the prism. Calculate the angle of the prism.
  2. Draw ray diagram when incident ray falls normally on one of the two equal sides of a right angled isosceles prism having refractive index $\mu = \sqrt{3} . $
→
Potential at an instant $t$ in an ac circuit is $E=200 \sin 157 t . \cos 157 t$ volts and current is $I=\sin \left(314 t+\frac{\pi}{3}\right) \quad$ Amperes. In this condition calculate :
(a) frequency
(b) root mean square value of voltage
(c) impedance of the circuit
(d) power factor.
→
A light ray incident at grazing angle on the face AB of a prism ABC, follows the path shown in the figure. Obtain the relation between the angle of prism A and the refractive index $\mu$ of its material.
→
A potential difference $V$ is applied across a conductor of length $L$ and diameter $D.$ How is the drift velocity, $V_d,$ of charge carriers in the conductor affected when $(i) \ V$ is halved, $(ii) \ L$ is doubled and $(iii) \ D$ is halved? Justify your answer in each case.
→
Explain the construction of compound microscope with the help of figure and derive the equation of magnification.
→
How is the mutual inductance of a pair of coils affected when:
  1. Separation between the coils is increased?
  2. The number of turns of each coil is increased?
  3. A thin iron sheet is placed between the two coils, other factors remaining the same? Explain your answer in each case.
→
A copper rod of length 1.0m is clamped at its middle point. Find the frequencies between 20Hz - 20,000Hz at which standing longitudinal waves can be set up in the rod. The speed of sound in copper is 3.8km/s.
→