Case study ( 4 Marks )

Question 14 Marks

Sound bounces off a solid or a liquid like a rubber ball bounces off a wall. Like light, soundgets reflected at the surface of a solid or liquid and follows the same laws of reflection. The directions in which the sound is incident and is reflected make equal angles with the normal to the reflecting surface at the point of incidence, and the three are in the same plane. If we clap near a suitable reflecting object such as a tall building or a mountain, we will hear the same sound again a little later. This sound which we hear is called an echo. The sensation of sound persists in our brain for about $0.1\ s$. To hear a distinct echo the time interval between the original sound and the reflected one must be at least $0.1\ s$. Hence, for hearingdistinct echoes, the minimum distance of theobstacle from the source of sound must be $17.2\ m$. Thisdistance will change with the temperature ofair. Another phenomenon of reflection of sound is reverberation.A sound created in a big hall will persist byrepeated reflection from the walls until it isreduced to a value where it is no longeraudible. The repeated reflection that resultsin this persistence of sound is called reverberation. Excessive reverberation is highly undesirable.
(i) Which of the following is true related to reflection of sound?
$(a)$ Directions in which the sound is incident and is reflected make equal angles with the normal to the reflecting surface at the point of incidence.
$(b)$ Incident wave reflected wave and normal lies in same plane
$(c)$ Both a and b are true.
$(d)$ None of these
(ii)For hearing distinct echoes, the minimum distance of the obstacle from the source of sound must be
$(a)$ $10m$
$(b)$ $20m$
$(c)$ $17.2m$
$(d)$ None of these
(iii) Excessive reverberation is
$(a)$ Desirable phenomenon
$(b)$ Undesirable phenomenon
$(c)$ Does not exist
$(d)$ None of these
(iv) A person makes sound near a obstacle and heard the echo after 1 s. What is the distance of the obstacle from the person if the speed of the sound, v is taken as 346 m/s?
(v) State law of reflection of sound.

Answer

$(i) c$
$(ii) c$
$(iii) b$
$(iv)$ Given,
Speed of sound, $v = 346\ m/s$
Time taken for hearing the echo, $t = 1\ s$
Distance travelled by the sound$= v × t = 346\ m/s \times 1\ s = 346\ m$
In $1$ s sound has to travel twice the distance between the obstacle and the person.
Hence, the distance between the obstacle and the person$= 346/2 = 173\ m$.
$(v)$ Law of reflection states that The directions in which the sound is incident and is reflected make equal angles with the normal to the reflecting surface at the point of incidence, and the three that is reflected wave, incident wave and normal to surface are in the same plane.

View full question & answer→

Question 24 Marks

A violin and a flute may both be played the same time in an orchestra. Bothsounds travel through the same medium,that is, air and arrive at our ear at the sametime. Both sounds travel at the same speedirrespective of the source. But the soundswe receive are different. This is due to thedifferent characteristics associated with thesound. Pitch is one of the characteristics.How the brain interprets the frequency ofan emitted sound is called its pitch. The fasterthe vibration of the source, the higher is the frequency and the higher is the pitch. The magnitude of the maximumdisturbance in the medium on either side ofthe mean value is called the amplitude of thewave. It is usually represented by the letter $(A)$.The loudness or softness of a sound isdetermined basically by its amplitude. Theamplitude of the sound wave depends uponthe force with which an object is made tovibrate. If we strike a table lightly, we hear asoft sound because we produce a sound waveof less energy (amplitude).
The quality or timber of sound is thatcharacteristic which enables us to distinguishone sound from another having the same pitchand loudness. The sound which is morepleasant is said to be of a rich quality. A sound of single frequency is called a tone. The sound which is produced due to a mixture of several frequencies is called a note and is pleasant to listen to. Noise is unpleasant to the ear! Music is pleasant to hear and is of rich quality.
(i) Pitch of sound is higher when
$(a)$ Vibration of source of sound is higher
$(b)$ Vibration of source of sound is Lower
$(c)$ Independent of vibration of source of sound
$(d)$ None of these
(ii) Loudness and softness of sound depends upon
$(a)$ Frequency of sound
$(b)$ Amplitude of sound
$(c)$ Wavelength of sound
$(d)$ None of these
(iii) Sound of single frequency is called
$(a)$ Note
$(b)$ Tone
$(c)$ Noise
$(d)$ None of these
(iv)If we strike a table lightly, we hear asoft sound. If we hit the tablehard we hear a louder sound up to large distance. Why?
(v) Determine which of the following has higher pitch railway horn or guitar?

Answer

$(i) a$
$(ii) b$
$(iii) b$
$(iv)$ If we hit the table hard we hear a louder sound because A sound wave spreads out from its source. As it moves away from the source its amplitude as well as its loudness decreases. Louder sound can travel a larger distance as it is associated with higher energy.
$(v)$ Pitch of sound depends on the frequency of vibration of waves and if the frequency of vibration is higher we say that the sound has higher pitch. Pitch of the sound is the response of our ear. So, basically guitar has $6$ strings and the sharpness of each string increases on going below. On the other hand in car horns, there is flat pitch with high noise which can affect anyone’s heart too. As guitar has higher frequency than car horn as number of vibrations per unit time of guitar string are more than car.

View full question & answer→

Question 34 Marks

The distance between two consecutivecompressions $(C)$ or two consecutiverarefactions $(R)$ is called the wavelength.The wavelength is usually represented by λ (Greek letter lambda). Its $SI$ unit is meter $(m)$.
•If we can count the number of the compressions or rarefactions that cross us per unit time, we will get the frequency of the sound wave. It is usually represented by υ (Greek letter, nu). $SI$ unit is hertz (symbol, Hz).
•The time taken for one complete oscillation is called the time period of the sound wave. It is represented by the symbol T. Its $SI$ unit is second $(s)$.Frequency and time period are related asfollows: $υ=1/\lambda $
•The speed of sound is defined as the distance which a point on a wave, such as a compression or a rarefaction, travels per unit time.

speed, $v$ = distance / time
$v= \lambda /T = υ\lambda $
(i) SI unit of wavelength
$(a)$ m
$(b)$ Hertz
$(c)$ m/s
$(d)$ None of these
(ii)SI unit of Frequency
$(a)$ m
$(b)$ Hertz
$(c)$ m/s
$(d)$ None of these
(iii) Relation between frequency and time is given by
$(a)$ frequency and time are directly proportional
$(b)$ frequency and time are inversely proportional
$(c)$ There is no relation between them
$(d)$ None of these
$(iv)$ Define speed of sound. Give its formula in terms of wavelength and frequency
$(v)$ Define wavelength frequency and time period of longitudinal wave

Answer

$(i) a$
$(ii) b$
$(iii) b$
$(iv)$ The speed of sound is defined as the distance which a point on a wave, such as a compression or a rarefaction, travels per unit time.
speed, $v$ = distance / time
$v= \lambda /T = υ\lambda .$
$(v)$ The distance between two consecutive compressions $(C)$ or two consecutive rarefactions $(R)$ is called the wavelength.The wavelength is usually represented by $\lambda $ (Greek letter lambda). Its $SI$ unit is meter $(m)$.
If we can count the number of the compressions or rarefactions that cross us per unit time, we will get the frequency of the sound wave. It is usually represented by $υ$ (Greek letter, nu). $SI$ unit is hertz (symbol, $Hz$).
The time taken for one complete oscillation is called the time period of the sound wave. It is represented by the symbol $T$. Its $SI$ unit is second $(s)$.Frequency and time period are related as follows: $υ= 1/\lambda $.

View full question & answer→

Question 44 Marks

The individual particlesof the medium move in a direction parallel tothe direction of propagation of thedisturbance. The particles do not move fromone place to another but they simply oscillateback and forth about their position of rest.This is exactly how a sound wave propagates;hence sound waves are longitudinal waves.There is also another type of wave, calleda transverse wave. In a transverse waveparticles do not oscillate along the direction of wave propagation but oscillate up and downabout their mean position as the wave travels.Thus, a transverse wave is the one in whichthe individual particles of the medium move about their mean positions in a directionperpendicular to the direction of wavepropagation.
(i) Sound waves are
$(a)$ Transverse waves
$(b)$ Longitudinal wave
$(c)$ Both $a$ and $b$
$(d)$ None of these
(ii) Light is
$(a)$ Transverse waves
$(b)$ Longitudinal wave
$(c)$ Both $a$ and $b$
$(d)$ None of these
(iii) In case of Longitudinal waves
$(a)$ The particles do not move fromone place to another but they simply oscillateback and forth about their position of rest
$(b)$ The particles move fromone place to another
$(c)$ The particles move up and down.
$(d)$ None of these
(iv) When stone is dropped in water; waves are generated of which types?
(v) Differentiate between longitudinal wave and transverse waves.

Answer

$(i) b$
$(ii) a$
$(iii) a$
$(iv)$ When stone is dropped in water. Waves are generated where water particles are moving up and down and propagated away from dropping point .hence this is sign of transverse waves. Hence transverse waves are produced when stone is dropped in water.
(v) Following are differentiated points

No	Longitudinal waves	Transverse waves
$1$	The medium, in the case of a longitudinal wave, moves in the same way to wave direction	The medium, in case of a transverse wave, moves perpendicular to wave direction
$2$	This wave is made up of compressions and rarefactions	This wave is made up of crests and troughs
$3$	example of a longitudinal wave is sound wave	An example of a transverse wave is the Light

View full question & answer→

Question 54 Marks

Sound is produced by vibrating objects. The matter or substance through which sound is transmitted is called a medium. It can be solid, liquid or gas. Sound moves through a medium from the point of generation to the listener. When an object vibrates, it sets the particles of the medium around it vibrating. The particles do not travel all the way from the vibrating object to the ear. Sound waves are characterized by the motion of particles in the medium and are called mechanical waves.When a vibrating objectmoves forward, it pushes and compresses theair in front of it creating a region of highpressure; this region is called a compression$(C)$.When the vibrating object moves backwards,it creates a region of low pressure calledrarefaction $(R)$. Hence sound is longitudinal wave.
(i) Sound waves are
$(a)$ Mechanical waves
$(b)$ Electromagnetic wave
$(c)$ Transverse waves
$(d)$ None of these
(ii) Sound travel in medium with
$(a)$ Compression and rare fraction
$(b)$ Crest and trough
$(c)$ Both can be possible
$(d)$ None of these
(iii) Compression is the region of
$(a)$ High pressure
$(b)$ Low pressure
$(c)$ Medium pressure
$(d)$ None of these
(iv) What is sound and how is it produced?
(v) Why sound wave is called as longitudinal wave?

Answer

$(i) a$
$(ii) a$
$(iii) a$
$(iv)$ Sound is vibrations created by object. When body vibrates, it forces the adjacent particles of the medium to vibrate. This results in disturbance in the medium, which travels as waves an reaches the ear hence sound is produced.
$(v)$ The vibration of medium that travels parallel to direction of wave or along in the direction of the wave is called longitudinal wave. The direction of particles of medium vibrates parallel to direction of propagation of disturbance. Therefore a sound is called longitudinal waves.

View full question & answer→

Science Case study ( 4 Marks )

Take a timed test