Download App

Waves — Physics STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 SciencePhysicsWaves5 Marks
Question
  1. What are beats? Name the basic phenomenon due to which beats are produced.
  2. Two sources of sound are producing waves of frequency n1 and n2, where (n1 - n2) is small, show mathematically that the beat frequency is (n1 - n2).
✓

Answer

  1. Beats: The waxing and waning of sound due to interaction between two slightly different frequencies. If y, and v, are the two frequencies vb = |v1 - v2|.

Beats are heard only when |v1 - v2l< 10, since the sound persist in our ears for $\frac{1}{10}\text{th}$ of a second.

  1. When n, and n, are two frequencies represented by $\text{y}_1=\text{A}\sin2\pi\text{n}_1\text{t}$ and $\text{y}_2=\text{A}\sin2\pi\text{n}_2\text{t},$ we get on superposition,

$\text{y}=\text{y}_1+\text{y}_2$

$=2\text{A}\cos\pi\Big(\frac{\text{n}_1-\text{n}_2}{2}\Big)\text{t}\sin2\pi\Big(\frac{\text{n}_1\text{n}_2}+{2}\Big)\text{t}$

Amplitude $=2\text{A}\cos2\pi\Big(\frac{\text{n}_1-\text{n}_2}{2}\Big)\text{t}$ becomes maximum, when $2\pi\text{t}\Big(\frac{\text{n}_1-\text{n}_2}{2}\Big)=0,2\pi...\text{N}\pi\text{ i.e., }\text{n}_1-\text{n}_2=\frac{2\text{N}\pi}{2\pi\text{t}}=\frac{\text{N}}{\text{t}}=\text{N}.$ n where n is the beat frequency-the number of times the maxima and minima is repeated in one second. 

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 "5 Marks Questions" from Waves→Waves — all question types→Physics STD 11 Science question papers→Rajasthan Board STD 11 Science question papers→Rajasthan Board question paper generator→

Similar questions

A cord of negligible mass is wound round the rim of a fly wheel of mass 20 kg and radius 20 cm. A steady pull of 25 N is applied on the cord as shown in Fig. 6.31. The flywheel is mounted on a horizontal axle with frictionless bearings.
(a) Compute the angular acceleration of the wheel.
(b) Find the work done by the pull, when 2m of the cord is unwound.
(c) Find also the kinetic energy of the wheel at this point. Assume that the wheel starts from rest.
(d) Compare answers to parts (b) and (c).
→
If 28 × 1023 molecules of a gas strike a surface of area 14cm2 normally per second with velocity of 500 ms-1 and rebound in the opposite direction with the same speed find the pressure exerted by the gas on the surface if mass of each molecule is 5 × 10-23 g.
→
A chain of length l and mass m lies on the surface of a smooth sphere of radius R>1 with one end tied to the top of the sphere.
  1. Find the gravitational potential energy of the chain with reference level at the centre of the sphere.
  2. Suppose the chain is released and slides down the sphere. Find the kinetic energy of the chain, when it has slid through an angle $\theta.$
  3. Find the tangential acceleration $\frac{\text{dv}}{\text{dt}}$ of the chain when the chain starts sliding down.
→
Find the value of $\frac{\text{t}}{\tau}$ for which the current in an LR circuit builds up to:
  1. 90%,
  2. 99%
  3. 99·9% of the steady-state value.
→
The bob of a pendulum at rest is given a sharp hit to impart a horizontal velocity $\sqrt{10\text{gl}},$ where l is the length of the pendulum. Find the tension in the string when,
  1. The string is horizontal.
  2. The bob is at its highest point.
  3. The string makes an angle of 60° with the upward vertical.
→
Write the law of force for simple harmonic motion and prove that $T=2 \pi \sqrt{\frac{m}{ k }}$.
→
Through what potential difference should an electron be accelerated to give it a speed of: 
  1. 0.6c
  2. 0.9c
  3. 0.99c
→
For the wave described in Exercise 15.8, plot the displacement (y) versus (t) graphs for x = 0, 2 and 4cm. What are the shapes of these graphs? In which aspects does the oscillatory motion in travelling wave differ from one point to another: amplitude, frequency or phase?
→
Describe surface tension on the basis of molecular forces.
→
A train runs along an unbanked circular track of radius 30m at a speed of 54km/h. The mass of the train is 106kg. What provides the centripetal force required for this purpose - The engine or the rails ? What is the angle of banking required to prevent wearing out of the rail?
→