Chapter 1 Simple harmonic motion & waves

Question 1

What is simple harmonic motion?

Answer 1

simple harmonic motion is a to-and-fro oscillatory motion in which the acceleration of the body is directly proportional to the displacement of the body from the main position and it is always directed toward the mean position.

Question 2

Think of several examples in everyday life of motion that are simple harmonic motions.

Answer 2

Example of SHM
(i) motion of a simple pendulum
(ii) motion of a ball in a bowl
(iii) the motion of the mass-spring system
(iv) motion of a pendulum of a clock

Question 3

What is meant by damped oscillations? How damping progressive reduces the amplitude of oscillation.

Answer 3

The oscillations of a system in the presence of some resistive force are called damped oscillations. for example, Shock absorbers in automobiles are one practical application of damped motion.
vibratory motion of Ideal systems in the absence of any friction or resistance continues indefinitely under the action of a restoring force. Practically, in all systems, the force of friction Retard the motion, so the systems do not osculate indefinitely. the friction reduces the mechanical energy of the system as time passes, and the motion is said to be damped. this damping Progressively reduces the amplitude of the motion.

Question 4

How can you define the term wave motion?

Answer 4

Wave motion
“wave is a disturbance in the medium which causes the particles of the medium to undergo vibratory motion about their mean position in equal intervals of time.” (OR) “Waves are produced when a body vibrates or oscillates about its mean position”

Question 5

Difference between mechanical waves and electromagnetic waves

Answer 5

Mechanical waves:
“The waves which require any material medium for their propagation are called mechanical waves.”
Examples:
Water waves, sound waves and waves on spring and spring are called mechanical waves.

Electromagnetic waves:
“the waves with do not require any material medium for their propagation are called electromagnetic waves”
Example:
radio waves, television waves, X-rays, heat waves, light waves etc are electromagnetic waves.

Question 6

Difference between longitudinal and transverse waves.

Answer 6

Longitudinal waves:

1. the weight in which the particles of the medium move back and forth along the direction of propagation of the waves are called longitudinal waves.
2. Examples:
   Wave moving along a spring sound waves etc.

Transverse waves:

1. the wave in which the motion of particles of the medium is perpendicular to the motion of a wave is called transverse wave.
2. Examples:

Transverse waves on a slinky, waves on the surface of water, light waves etc.

Question 7

Define vibratory motion.

Answer 7

The two and slow motion of a body about its mean position is known as vibratory motion.
Example:
the motion of a simple pendulum about its mean position motion, the motion of a see-saw about its mean position, etc.

Question 8

How a spider detects his prey?

Answer 8

Spider detect his Prey due to vibration produced in its web.

Question 9

State Hooke’s law and write its equation.

Answer 9

If the force ‘F’ applied on a mass attached to the spring will displace the spring through distance ‘X’, then this force is directly proportional to the change in the length or distance moved by mass ‘m’.

Mathematically, F ∝ x or F = -Kx

Here, the negative sign shows that force is always directed to the mean position.

K is called the spring constant its value is K = -F/x

Question 10

define elastic restoring force.

Answer 10

The force which pushes or pulls the object performing oscillatory motion towards the mean position is called Restoring force.

Mathematically, restoring force is defined as the following:

                    F = -kx

Where negative signs show that the force is always directed towards the mean position.

Question 11

Define a spring constant and write its formula.

Answer 11

“Spring Constant is defined as the ratio of applied force to the change in length of a spring”

Mathematically, the Spring Constant is written as k = F/x

SI unit of spring constant SI unit of spring constant ‘k’ is Nm-1

Question 12

Write K.E. and P.E. at different positions of a mass-spring system.

Answer 12

At mean position: K.E. = Max, P.E. = 0
at extreme position +A: K.E. = 0, P.E. = Max, At extreme position -A:
K.E. = 0, P.E. = Max

Question 13

How many times a human eardrum can oscillate in one second?

Answer 13

A human eardrum can oscillate back and forth up to 20,000 times in one second

Question 14

what is the displacement of an object in SHM when the kinetic and potential energies are equal?

Answer 14

When the object is at rest, its K.E. and P.E., both are zero. Thus, its displacement is zero.

Question 15

Define a simple pendulum and write its formula for its time period.

Answer 15

A simple pendulum consists of a small bob of mass ‘m’ suspended from a light string of length ‘l’ fixed at its upper end.

The formula of Time Period:
The time period ‘T’ of a simple pendulum of length ‘l’ Is given by the following formula.

                         T =  2π √l/g

where ‘g’ is the gravitational acceleration of the bob of a simple pendulum.

Question 16

what is meant by the time period of a simple pendulum?

Answer 16

the time period of a pendulum is the time to complete one cycle or vibration.

Question 17

what factors do not effect time period of a simple pendulum?

Answer 17

the time period of a pendulum is independent of the mass and amplitude of a simple pendulum.

Question 18

Define restoring force. In the vibratory motion of a simple pendulum which component of the weight acts as restoring force?

Answer 18

Elastic restoring force:
“The force which pushes or pulls the object performing vibratory motion or oscillatory motion towards mean position is called restoring force.”

Component of a weight that acts as Restoring Force:
“the restoring force that causes the pendulum to undergo simple harmonic motion is the component of gravitational force ‘mg sinθ’ tangent to the path of motion”

Question 19

Tell whether or not these motions are examples of simple harmonic motions.

(a) the up and down motion of a leaf in a water pond.

(b) motion of the ceiling fan.
(c) motion of hands of the clock.

(d) motion of a plucked string fixed at both ends

(e) movement of honey bees.

Answer 19

a) the up and down motion of a leaf in a water pond. (Yes)

(b) motion of the ceiling fan. (No)
(c) motion of hands of the clock. (Yes)

(d) motion of a plucked string fixed at both ends. (Yes)

(e) movement of honey bees. (No)

Question 20

Characteristics/features of a simple harmonic motion.

Answer 20

(i) A body executing SHM vibrates about a fixed position; called the mean position.

(ii) Its acceleration is always directed towards the mean position.

(iii) The magnitude of the acceleration is always directly proportional to its displacement from the mean position i.e., acceleration will be zero at the mean position while it will be maximum at extreme positions.

(iv) Its velocity is maximum at the mean position and zero at extreme positions.

Question 21

What is meant by vibration?

Answer 21

One complete round trip of a vibrating body about its mean position is called one vibration.

Question 22

What is meant by frequency? Write its SI unit.

Answer 22

“The number of vibrations or cycles of a vibrating body completed in one second is called frequency ‘f’ “

The si unit of frequency is vibration per second or cycles per second or HZ.

Question 23

Define time period.

Answer 23

“Time taken by a vibratory body to complete one vibration is called time period” It is denoted by T

Question 24

Define amplitude.

Answer 24

“The distance of the particles of the stretched string from its rest position or mean position is called amplitude”

Question 25

What is the relation between frequency and Time Period?

Answer 25

Mathematically; frequency 'f' is reciprocal of time period 'T' i.e. f = 1/T

Question 26

What is meant by wavelength?

Answer 26

For Longitudinal Waves: "The distance between two consecutive compressions or rare fractions is called wavelength." For Transverse Waves: "The distance between two consecutive crests or troughs is called wavelength."

Question 27

Define wave motion.

Answer 27

"A Wave is a disturbance in the medium which causes the particles of the medium to undergo vibratory motion about their mean position in equal intervals of time"

Question 28

How are crests and troughs produced in water waves?

Answer 28

Dip one end of a pencil into a tub of water, and move up and down vertically, the disturbance in the form of ripples produces water waves, which move away from the source. When the waves reach a small piece of cork floating near the disturbance, it moves up and down about its original position while the wave will travel outwards. The net displacement of the cork is zero. The cork repeated its vibratory motion about its mean position.

Question 29

What are the main types of waves?

Answer 29

(i) Mechanical waves (ii) Electromagnetic waves

Question 30

Define Mechanical Waves.

Answer 30

"The waves which require any material medium for their propagation are called mechanical waves. " Example: Water waves, sound waves, waves on a spring and string are called mechanical waves.

Question 31

Define electromagnetic waves.

Answer 31

"The waves which do not require any material medium for their propagation are called electromagnetic waves" Example: Radio waves, television waves, X-rays, heat waves, light waves, etc.

Question 32

Types of mechanical waves.

Answer 32

(i) Longitudinal mechanical waves (ii)Transverse mechanical waves

Question 33

Define Longitudinal waves.

Answer 33

"The waves in which the particles of the medium move back and forth along the direction of propagation of the wave are called longitudinal waves." Example: Waves moving along a spring, sound waves, etc.

Question 34

In which medium speed of longitudinal waves?

Answer 34

Longitudinal waves move faster through solids than through liquids and gases.

Question 35

Why the speed of transverse waves in solids is less than half the speed of longitudinal waves?

Answer 35

Transverse waves move through solids at a speed of less than half of the speed of longitudinal waves. It is because the restoring force exerted during this up-and-down motion of particles of the medium is less than the restoring for exerted by a back-and-forth motion of particles of the medium in the case of longitudinal waves.

Question 36

Define transverse waves.

Answer 36

The waves in which the motion of particles of the medium is perpendicular to the motion of a wave are called transverse waves.

Question 37

Differentiate between the crest and trough of transverse waves.

Answer 37

Crests: The crests are the highest points of particles of the medium form the mean position. Troughs: The troughs are the lowest points of the particles of the medium from the mean position.

Question 38

Define mechanical waves and why these waves cannot pass through the vacuum.

Answer 38

Mechanical waves require a medium for their propagation. So, they cannot pass through the vacuum.

Question 39

What are the factors on which the amount of energy carried by the waves depends?

Answer 39

The amount of energy carried by the wave depends upon the following factors: (I) Amplitude: The greater the amplitude of a wave, the greater the amount of the energy transferred by the wave. (ii) Frequency: If we shake the string faster, we give more energy per second to produce a wave of higher frequency, and the wave delivers more energy per second to particles of string as it moves forward.

Question 40

Why does a high-frequency wave carry more energy than a low-frequency wave?

Answer 40

To generate a high-frequency wave requires more energy per second than to generate a low-frequency wave. Thus, a high-frequency wave carries more energy than a low-frequency wave of the same amplitude.

Question 41

How do geophysicists learn about the internal structure of Earth? (OR) what are seismic waves and their advantage?

Answer 41

An earthquake produces waves through the body of the earth in the form of seismic waves. by studying such waves, Geophysicists learn about the internal structure of the earth and information about the occurrence of future Earth activity.

Question 42

What do the dark and bright fringes on the screen of the ripple tank represent?

Answer 42

Water waves are transverse waves. the bright fring on the screen of represent represents a crest while the dark fring represents a trough.

Question 43

What is a ripple tank? (OR) what do you know about ripple tanks? (OR) what is the function of a ripple tank?

Answer 43

It is a device used to produce and study the characteristics of water waves.

Question 44

What is meant by the reflection of waves?

Answer 44

When waves moving in one medium fall on the surface of another medium, they bounce back into the first medium such that the angle of incidence is equal to the angle of reflection this phenomenon is called reflection of waves.

Question 45

Define the diffraction of waves.

Answer 45

“The bending or spreading of waves around sharp edges or corners obstacles is called a diffraction”

Question 46

Define the wave equation and write down its formula.

Answer 46

The relationship between velocity (v), frequency (f) and wavelength (λ) of the wave is called a wave equation. Formula: Mathematically, the wave equation is given as v = fλ