General Waves Properties - Self Assessment Questions And Text Book Exercise

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Physics For Class X
Unit 10: General Waves Properties
Self Assessment Questions

Q.1: Distinguish between transverse and longitudinal waves
Ans: Difference Between Transverse Waves And Longitudinal Waves:

S.NO.	Transverse Waves	Longitudinal Waves
1.	In transverse wave, particles of the medium vibrates perpendicular to the direction of propagation of waves.	In longitudinal wave, particles of the medium vibrates parallel to the direction of propagation of waves.
2.	This wave is made up of crests and troughs.	This wave is made up of compressions and rarefactions.
3.	The production of this wave can take place in liquid and gas mediums only.	The production of this wave can take place in any medium - solid, gas, or liquid.
4.	The polarization or alignment of this wave is certainly possible.	The polarization or alignment of this wave does not happen.
5.	This wave acts in two dimensions.	This wave acts in one dimension.
6.	An example of a transverse wave is the light wave.	An example of a longitudinal wave is the sound wave.

Q.2: Wave motion transfers energy without moving matter. Justify this statement with an example.
Ans: Waves are means of energy transfer without transfer of matter:
The wave is a disturbance in a medium that transfer energy from one place to another, but waves can not move matter the entire distance.

OR

A method of transport energy from one point to another point without transfer of matter is called wave.
Disturbance of medium is cause of formation of wave like, waves can be produced by using a rope, slinky spring and water waves in ripple tank.

Example No.1:
When the calm water surface is disturbed by a stone dropping into it, circular water ripples spread out from the point where the stone hits the water. Similarly the continuous disturbance of the water surface by the blasts of the wind caused by a helicopter hovering above creates water waves that move outwards. If we place a cork on the surface of water. We observed that when the waves reaches the cork, it will move up and down along the motion of water particles by getting energy from waves but remain at its position. Thus the disturbance on the water surface moves outwards, carrying energy, and no water, because after the waves pass, the cork on water remains where it was before the wave was produced.

Example No.2:
A tide can travel many kilometres. The water moves up and down - a disturbance that travels in a wave, transferring energy, not matter. Let's consider the example of a buoy bobbing in the ocean. The buoy is moved up and down by the waves that pass by it but doesn't move directionally across the water. Waves transfer energy but not mass. When particles in water become part of a wave, they start to move up or down. This means that kinetic energy (energy of movement) has been transferred to them. As the particles move further away from their normal position (up towards the wave crest or down towards the trough), they slow down. This means that some of their kinetic energy has been converted into potential energy - the energy of particles in a wave oscillates between kinetic and potential energy.
This activity shows that water waves like other waves transfer energy from one place to another without transferring matter, i.e., water.

Q.3: What is the main difference between mechanical and electromagnetic waves.
Ans: Difference Between Mechanical Waves And Electromagnetic Waves:

S.NO.	Mechanical Waves	Electromagnetic Waves
1.	Mechanical waves are such waves that need a medium for propagation.	Electromagnetic waves are such waves that do not need a medium for propagation.
2.	Mechanical waves are produced by vibratory motion in the respective medium.	Electromagnetic waves are produced by a changing of electric and magnetic fields.
3.	Mechanical waves consist of transverse as well longitudinal waves.	Electromagnetic only comprised of a transverse wave in nature.
4.	Mechanical waves cannot travel through the vacuum.	Electromagnetic waves travel through the vacuum at the speed of 3×108 m/s.
5.	All mechanical waves travel through their media at different speeds depending upon the physical properties of the respective medium.	All electromagnetic waves can travel through transparent media at different speeds depending upon the refractive index of the respective medium.
6.	Sound waves, water waves and seismic waves are some examples of mechanical waves.	Radio waves, microwaves, light waves, U.V waves and infrared waves are some examples of electromagnetic waves.

Q.4: How spherical wavefronts are produced in the ripple tank?
Ans: In a ripple tank, a spherical dipper can produce circular waves. These waves have a circular wavefront. When the rippler is attached with a point has spherical ball and lowered it so that it just touches the surface of the water, circular waves will be produced.
Circular waves can also be produced by dropping a single drop of water into the ripple tank.

Q.5: What is the difference between displacement and amplitude of the wave?
Ans: Difference Between Displacement And Amplitude Of the Wave:
Displacement is a maximum distance covered by a body between two points. The displacement of a particle on a wave is a distance in a specific direction from its rest/ equilibrium position. It is a vector quantity and may be positive or negative.
Displacement is associated with the visible physical movement e.g. Swing of a pendulum vibration on the string of a guitar.

Amplitude of a wave refers to the maximum displacement moved by a point on the medium (on a vibrating body) from its rest or mean position. It is the height of a crest or depth of a trough measured from the rest position. It refers to the scalar or vector quantity depends on field size.
Amplitude is normally associated with conceptual waves. e.g. Propagation of sound waves, pressure waves etc.

Q.6: Drive the relation between wave, speed and frequency.
Ans: Relation Between Wave speed And Frequency:
The wave is a disturbance in a medium that transfer energy from one place to another. It travels from one place to another and hence has a specific velocity. This called the velocity (Speed) of the wave and is denoted by

Velocity = Distance traveled / time taken or

v = S / t

Let us consider for a wave,
If the time taken by the wave to move from one point to another is equal to its time period 'T', then the distance travelled by the wave will be equal to one wavelength = λ

The speed of wave can also be written as V = fλ

OR

Frequency (f): is the number of complete waves produced by a source per unit of time. Thus,
Frequency (f)= Number of complete waves produced / time taken
If the number of waves produced = 1
And the time is taken = T
Then f = 1/T
In general; frequency is also defined as the reciprocal of the period.

Wave Speed(v): is the speed at which a waves travels. It is defined as the distance travelled by a given point on the wave, such as a crest in a given interval of time.
Speed = Distance travel per taken time.
Let us consider for a wave,
Distance travelled by the wave = wavelength = λ
And time taken = T, then,

The speed of wave can also be written as V = fλ

Q.7: Calculate the frequency of seconds pendulum?
Ans: Frequency Of Second Pendulum:
The frequency is the reciprocal of the time period. In other words, frequency is the number of oscillations per second. Frequency 'f' is the reciprocal of the time period (represented by 'T'). That is:
Formula:

The second pendulum is that pendulum whose time period is 2s. In other words, a second's pendulum takes 2 seconds to complete one full oscillation. So, the pendulum takes 1 second to swing from the right maxima to the left maxima and another second to swing back. So, that makes 2 seconds in total. 

T = 2s ……… (2)

Substituting (2) in (1) we get the frequency of a second's pendulum as:

Therefore, the frequency of the second pendulum is 0.5 Hz.

OR

Data:
Frequency = f = ?
Time period of second pendulum = T = 2s

Formula:

Calculation:

Answer:
Therefore, the frequency of the second pendulum is 0.5 Hz.

Q.8: Which component of force (weight) is responsible for the oscillatory motion of a simple pendulum?
Ans: Component Of Force For Oscillatory Motion Of A Simple Pendulum:
Restoring force (a component of gravitational force) is responsible for the oscillatory motion of a pendulum.
Let the displacement of the pendulum bob is the arc length s.
The weight mg has components mg cos𝜃 along the string and mg sin𝜃 tangent (perpendicular) to the arc.
Tension in the string exactly cancels the component mg cos𝜃 parallel to the string.
This leaves a net restoring force directed back toward the equilibrium position that runs tangent to the arc and equals -mg sin𝜃. Thus the component of force mg cos𝜃 is responsible for the oscillatory motion of a simple pendulum.

Q.9: At what position acceleration of the simple oscillatory pendulum is maximum, and why?
Ans: A simple oscillatory pendulum has its maximum acceleration at the two extreme position of the swing. At either extreme position of maximum displacement the force is greatest and is directed toward the equilibrium position, the velocity (v) of the mass becomes zero, so its acceleration is maximum at this point, and the mass changes direction.

Q.10: The normal reaction of the bowl on the ball is in the upward direction. Why is it not moving in that direction?
Ans: When the ball is at the mean position, that is, at the centre of the bowl, the net force acting on the ball is zero. In this position, the weight of the ball acts downward and is equal to the upward normal force of the surface of the bowl.
When the ball moves through the centre of the bowl, the weight of the ball cancels out the upward normal force. Hence the ball does not move in upward direction.

Q.11: Where is the ball in the bowl system moving fastest, slowest?
Ans: A ball in the bowl system moves fastest in its mean position due to the inertia. While going towards the extreme position, the speed of the ball decreases due to the restoring force which acts towards the mean position. At the extreme position, the speed of ball starts to decrease and ball stops for a while and then again moves towards the mean position.

Q.12: What will happen if there is no damping in an oscillating drum skin?
Ans: An oscillation that fades away over time in the presences of some resistive force is called damped oscillation. So if there is no damping in an oscillating drum skin, it will vibrate continuously and will not slow down or stop. In such system the drum skin continuously resonance and the amplitude, frequency and energy all remain constant.

Text Book Exercise