Waves

Question 1

What is a wave?

Answer 1

form of disturbance which travels through a material medium due to the repeated periodic motion of particles about their mean positions

Question 2

characteristics of waves:

Answer 2

(i) particles of medium execute small vibrations about their mean positions but the particles are not permanently displaced in the direction of propagation of the wave.
(ii) Each successive particle of the medium executes a motion along/perpendicular to the line of travel of the wave.
(iii) During wave motion only transfer of energy takes place but not that of a portion of the medium.

Question 3

Types of waves:

Answer 3

mechanical
electromagnetic
matter

Question 4

Mechanical waves:

Answer 4

Mechanical waves can be produced or propagated only in a material medium like waves on water surface, waves on strings, sound waves etc.

Question 5

Electomagnetic waves:

Answer 5

Waves which require no material medium for their production and propagation, i.e., they can pass through vacuum and any other material medium like visible light; ultra-violet light; radiowaves, microwaves etc.

Question 6

matter waves:

Answer 6

These waves are associated with moving particles of matter, like electrons, protons, neutrons etc
Two types:
(i) Transverse wave motion
(ii) Longitudinal wave motion

Question 7

Transverse wave:

Answer 7

Particles of the medium vibrate perpendicular to the direction in which the wave propagates like waves on strings, surface water waves and electromagnetic waves. disturbance that travels is not a result of vibrations of particles but it is the oscillation of electric and magnetic fields which takes place perpendicular to the direction in which the wave travels

Question 8

longitudinal wave:

Answer 8

Particles of the medium vibrate to and fro about their mean position along the direction of propagation of energy. Also called pressure waves like sound waves

Question 9

ω=

Answer 9

2pi/T

Question 10

Newton Laplace formula

Answer 10

According to Laplace, during propagation of sound waves, change takes place under adiabatic conditions because gases are thermal insulators and compressions and rarefractions are taking place very rapidly.

Question 11

Factors Influencing Velocity of Sound

Answer 11

(i) inversely proportional to square root of density of gas.
(ii) independent of change in pressure of gas, when temp remains constant.
(iii) directly proportional square root of absolute temperature.
(iv) this in moist air is greater than that in dry air.
(v) If wind flows at an angle θ to the direction of propagation of sound, the velocity of sound is v + w cos θ, where w is the velocity of wind.

Question 12

General Equation of Progressive Waves

Answer 12

y (x,t) = A sin (kx — ωt + Ф)

Question 13

The Principle of Superposition of Wave

Answer 13

When waves meet simultaneously at a point in a medium, net displacement at a given time is algebraic sum of displacements due to each wave at that time.

Question 14

Standing waves or Stationary waves

Answer 14

When two sets of progressive waves having the same amplitude and time period/frequency/ wavelength travelling with same speed along the same straight line in opposite directions superimpose, a new set of waves are formed

Question 15

Frequency of the Stretched String

Answer 15

nodes are formed at fixed ends and antinode at middle point. The frequency of fundamental mode of vibration (or first harmonic) is given by L=1/2λ

Question 16

Beats

Answer 16

phenomenon of regular rise and fall in intensity of sound, when two waves of nearly equal frequencies travelling along the same line and same direction superimpose each other

Question 17

beat frequency

Answer 17

number of beats per second

Question 18

v(b) =

Answer 18

v(b) = (v1-v2)