Physics IMPSs for VNJC

 

Wave Physics Questions and Answers

1. What is wave?
Ans.: Wave is a periodic and regular disturbance of energy and momentum from one point of the medium to another without any flow of material of medium.

2. What do you mean by electromagnetic waves?
Ans.: Electromagnetic waves are generated due to periodic vibrations in electric and magnetic fields.

3. What do you mean by matter waves? (1 mark)
Ans. The waves always associated with any object in motion are called matter waves.

4. What are mechanical waves. State its examples. (2 marks)
Ans.: (i) Waves which require material medium for their propagation are called mechanical waves.
(ii) Water waves, sound waves, seismic waves and waves along a stretched string are some of the examples of mechanical waves.

5. What are travelling or progressive wave? Name the types of progressive wave? (2 marks)
Ans.:
(i) Waves which travel continuously in the same direction in the given medium without change of form unless stopped by some external force agencies are called as travelling or Progressive waves.
(ii) Progressive waves can be identified as transverse waves and longitudinal waves depending upon the vibration of particles of the medium.

6. Define amplitude?
Ans. The maximum displacement of the particle of the medium from its mean position when a wave propagates through it is called as amplitude of the wave.

7. Define period of a wave? (1 mark)
Ans. Time taken by the particle of the medium to complete one vibration is the period of the wave.

8. Explain what is meant by phase of a wave.
Ans. The state of oscillation of a particle of medium at an instant when a wave propagates through it is called as phase of the wave.

9. Wave motion is double periodicity. Explain.
Ans.: Wave possesses double periodicity.
(i) Periodic in time: When a wave travels through a medium, at every location it repeats itself after equal intervals of time. This shows that wave motion is periodic in time.
(ii) Periodic in space: At any instant, the wave repeats itself at an equal distance or space. This shows that wave motion is periodic in space, Thus, Wave motion is a doubly periodic phenomena i.e. periodic in time and periodic in space.

10. State properties of medium for propagation of mechanical waves.
Ans. The properties required by a medium to propagate mechanical waves are:
(i) The medium should be elastic and continuous so that on removal of deforming forces, it regains its original state.
(ii) The medium should possess inertia so that energy is stored and transferred in the form of waves.
(iii) The medium should have negligible frictional resistance to avoid damping of oscillation of wave.

Q.12. What do we need to know to describe phase at a place? (2 marks)
Ans. In order to describe phase at a place, we need to know the displacement, direction of velocity and the number of oscillations of the particle at that place.

13. State characteristics of progressive wave? (2 marks)
Ans. Characteristics of progressive wave:
(i) All vibrating particle of the medium have same amplitude, period and frequency.
(ii) State of oscillation (phase) changes from particle to particle.
(iii) Progressive wave transfer energy through the medium.
(iv) The wave disturbance travels forward with a definite velocity.
(v) Each particle of medium executes a simple harmonic motion about its mean position with same amplitude.
(vi) There is a continuous change of phase from one particle to the next.
(vii) No particle of medium is permanently at rest.

Time period (T): The time required for a particle to complete one vibration is called period of wave. The S.I. unit of time period is second (s).

Frequency (n): The number of vibration performed by any particle of medium in one second is called frequency. The S.I. unit of frequency is hertz (Hz) or (s⁻¹). It is equal to the reciprocal of period.

n = 1 T

Q.15. Derive the relation between speed, frequency and wavelength of wave. (3 marks)
Ans.

Time period (T):
The time required for a particle to complete one vibration is called period of wave. The S.I. unit of time period is second (s).

Frequency (n):
The number of vibration performed by any particle of medium in one second is called frequency. It is equal to the reciprocal of period.
n = 1 T
The S.I. unit of frequency is hertz (Hz) or s⁻¹.

Wavelength (λ):
Wavelength of wave is the distance between any two successive particles of medium having same state of vibration. The S.I. unit wavelength is metre (m).

Speed (v):
The speed of wave is the distance covered by the wave in unit time, in the direction of wave-motion. The S.I. unit of speed is metre/second (m/s).

Relation between speed, wavelength and frequency of wave:
In periodic time (T), the wave covers a distance equal to wavelength (λ).
Hence, the distance (s) travelled by the wave in unit time,
s = λ T

But, the distance travelled by wave in unit time is its speed (v).
v = λ T

Since
1 T = n
v = nλ

Thus, speed of the wave is a product of its frequency and wavelength.