Oscillations and Waves: Important part-A 2 marks Short Questions and Answers

ANNA UNIVERSITY PART‒A QUESTIONS AND ANSWERS

1. Define forced and damped oscillations.

Damped Oscillation: In a real situation, if a body is set into vibrations, the amplitude keeps on decreasing because of frictional resistance to the motion and hence after some time the vibrations (or) oscillations will die. This type of oscillation is said to be a damped oscillation. In this oscillation (or) vibration, the body vibrates with its natural frequency.

Forced Oscillation: There are situations in which we need to give external force for the oscillations to sustain. This type of oscillation in which the body vibrates with a frequency other than natural frequency due to the external force applied in equal interval of time is called Forced Oscillation.

2. Define the term Simple harmonic motion.

(or) Mention the characteristics of SHM

Simple Harmonic motion is the motion in which the acceleration of a body is directly proportional to the displacement from a fixed point and is always directed towards the fixed point (or) equilibrium position.

(i) The motion of the particle is periodic.

(ii) The motion of the particle is along a straight line about its mean position.

(iii) The acceleration of the particle is proportional to the displacement and is directed towards its mean position.

3. Define torque.

Torque is the rotating force and is equal to the moment of the couple. Torque is the product of one of the forces forming couple and the perpendicular distance between the two opposite forces.

ADDITIONAL PART‒A QUESTIONS AND ANSWERS

1. What are the types of motion? give examples.

Based on the motion of the physical bodies, it can be classified into two types viz.

1. Translational motion, in which the motion of the body moves linearly with time.

Examples: Train moving in a track, Rocket launching etc.

2. Rotational (or) Oscillatory motion, in which the motion of the body repeat itself after regular interval of Time.

Examples: Bob moving in a pendulum clock, Beating of heart, Movement of Earth around the Sun etc.

2. Define Simple harmonic motion.

Simple Harmonic motion is the motion in which the acceleration of a body is directly proportional to the displacement from a fixed point and is always directed towards the fixed point (or) equilibrium position.

3. Categorize the types of SHM, with examples,

There are two types of simple Harmonic motions, viz

I. Linear Simple Harmonic motion: Here the displacement of the particle executing simple Harmonic motion is linear.

Examples:

i. Motion of Simple pendulum.

ii. Motion of point mass suspended with a spring etc.

II. Angular Simple Harmonic motion: Here the displacement of the particle executing simple harmonic motion is Angular.

Examples

i. Oscillations of a compound pendulum.

ii. Torsional oscillations etc.

4. Write down the characteristics of SHM.

The characteristics of simple harmonic motion are as follows.

(i) The motion of the particle is periodic.

(ii) The motion of the particle is along a straight line about its mean position.

(iii) The acceleration of the particle is proportional to the displacement and is directed towards its mean position.

5. Define Amplitude data and phase.

Amplitude: The Maximum distance covered by the body on either side of its mean position is called its Amplitude.

Phase: It is the physical quantity that express the instantaneous position and direction of motion of an oscillating system.

6. Define Time period and frequency. Give its relation.

Time Period: The smallest time required to complete one vibration (or) oscillation is known as time period.

Time period T = 2π / ω

 (or) T = 2π / √(Acceleration/ Displacement)

(or) T = 2π √(Displacement/Acceleration)

Frequency: The number of oscillations (or) vibrations made by a body per second is known as frequency of oscillation. It is the reciprocal of the time period.

The relation between time and frequency is n= 1/T

7. List out the types of Oscillatory motion.

There are three type of oscillatory motion, based on the force that is acting on the system, viz.

1. Free vibration

2. Damped Oscillation and

3. Forced Oscillation

8. What is ment by free vibration.

Free vibration: A system (or) body which vibrates freely without any resistance (Even air) (or) Frictional force is called free vibrations. In real situation this is not possible, because by nature always some resistance is offered to the oscillating system.

9. What is meant by damped vibrations? Give examples.

Damped Oscillation: In a real situation, if a body is set into vibrations, the amplitude keeps on decreasing because of frictional resistance to the motion and hence after some time the vibrations (or) oscillations will die. This type of oscillation is said to be a damped oscillation. In this oscillation (or) vibration, the body vibrates with its natural frequency,

Examples:

1. When a Pendulum is displaced from its equilibrium position, it oscillates with a decreasing amplitude and finally it come to rest.

2. If a mass its suspended in a spring and is set into vibration in air, it will take long time to come to rest, when compared to the same mass set into vibration in water.

10. What is meant by Forced vibrations? Give examples.

Forced Oscillation: There are situations in which we need to give external force for the oscillations to sustain. This type of oscillation in which the body vibrates with a frequency other than natural frequency due to the external force applied in equal interval of time is called Forced Oscillation.

Examples:

1. A Tuning fork set into vibration due to external force.

2. A floor vibrating due to Marching of soldiers.

3. A bob of simple Pendulum held in hand and then given number of swings by the hand.

11. What do you understand by the term DEAD BEAT? Give examples.

During oscillation motion, when the displacement decreases drastically without performing any oscillations, then the motion is set to be Over‒damped Oscillation (or) Dead beat.

Examples:

1. Pendulum moving in a very thick coil media.

2. Dead beat moving coil galvanometer.

12. What is Meant by critical damped motion? Give examples.

During oscillatory motion, when the displacement decreases to zero rapidly, then it is called critical damped motion.

1. Movement of pointer in voltmeter, Ammeter etc.

2. Sensitive galvanometers.

13. What is meant by under damped motion? Give examples.

During oscillatory motion, when the displacement (or) Amplitude decays with respect to the damping factor, then it is termed as under damped motion.

Examples:

1. Motion of a simple pendulum in air.

2. Motion of the coil in ballistic galvanometer.

14) What is moment of a force?

The moment of a force about a point is defined as the product of the magnitude of the force and the perpendicular distance from the point to the line of action of force.

15. Define wave motion and give its types.

Definition

A wave motion can be defined as a disturbance which travels in the material medium and is due to the repeated motion of the particles in the medium, about their mean position wherein the motion is being transferred from one particle to the next at regular interval of time.

Types

There are two types of waves, viz.,

(i) Transverse waves.

(ii) Longitudinal waves.

16. What is meant by transverse wave motion? Give examples

Transverse waves

It is the wave motion in which the particles of the medium vibrate about their mean position perpendicular (right angles) to the direction of propagation.

Examples:

(1) Waves produced on the surface of water in which the particles of the medium vibrate up and down

(2) Waves produced in stretched strings.

17. What is meant by longitudianl wave motion? examples.

Longitudinal waves

It is the wave motion in which the particles of the medium vibrate about their mean position along the same line as that of propagation of the wave.

Examples:

(1) Condensation & rarefactions produced in air by the vibratory motion of a tuning fork.

(2) Compressions & rarefactions in air when one end is fixed & other end is moved with piston in a cylinder [Kundt's tube experiment].

18. Write the differences between transverse and longitudinal waves.

Transverse wave motion

1. It is the wave motion in which the particles of the medium vibrates perpendicular the direction of propagation.

2. Crests & Troughs are formed

3. Transverse waves can travel through solids & liquids but not through gases.

4. Transverse waves can be reflected, diffracted and polarized.

Longitudinal wave motion

1) It is the wave motion in which the particles of the medium vibrates along the direction of propagation.

2) Compresions and rarefactions are formed.

3) Longitudinal waves can travel through any medium.

4) Longitudinal waves can't be be polarised.

19. What are the laws of transverse vibrations.

Laws of transverse vibrations

1) Law of length

The frequency of transverse vibrations of a stretched string is inversely proportional to its vibrating length under a constant stretching force.

i.e, n α 1/l

Where T & m are constant

2) Law of tension

For a string of given length and material, the frequency is directly proportional to the square root of the stretching force (Tension).

i.e., n α √T

Where l, m are constant

3) Law of mass

The frequency is inversely proportional to the square root of the mass per unit length, when the tension and the length are kept constant.

i.e., n  α  1/√m

Where T, l are constant.

20. Define standing waves (or) stationary waves with examples.

Stationary waves

When two identical progressive waves travel through a medium along the same line in opposite directions with equal velocities, they superimpose over each other and produces a new type of wave called as Standing wave (or) stationary wave.

They are called stationary waves because there is no flow of energy along the waves. In a stationary wave the points at which the displacement is zero are called nodes. The points at which the displacement maximum are called antinodes. In a stationary wave all the points between successive nodes will be in phase.

Examples

1) Waves along a string.

2) Waves along the air‒column of a pipe.

21. Define travelling waves (or) progressive waves. Give examples.

Progressive waves

In a travelling wave (or) progressive wave, the energy is transferred from one place to another by the continuous vibration of the particles in an elastic material medium about their equilibrium position.

In a travelling wave every point vibrates with same amplitude and the phase of vibration changes for different points along its path.

Examples

1) Waves passing through water.

2) Electromagnetic waves in which the electric and magnetic fields vary periodically at right angles to each other and to the direction of propagation.

22. List few differences between standing waves & travelling waves.

Travelling (or) Progressive waves

1) Travelling waves transfer energy from one end to another.

2) Energy flows across energy plane in the direction of the wave.

3) These will be advancement in wave direction.

4) Each particle of the medium executes SHM about its mean position with same amplitude.

5) No particles on the wave is Permanently at rest.

6) Phase changes continuously from point to point.

Standing (or) Stationary waves

1) Standing waves do not transfer energy from one end to another.

2) No energy flows across any plane.

3) No advancement of the wave in any direction.

4) Except nodes, all particles vibrates and executes SHM with different amplitude.

5) Nodes are permanently at rest.

6) All points between any pair of nodes vibrates in the same phase but the phase suddently reverses at each nodes.