Case Study Questions Class 11 Physics Chapter 15 Waves
CBSE Class 11 Case Study Questions Physics Waves. Important Case Study Questions for Class 11 Board Exam Students. Here we have arranged some Important Case Base Questions for students who are searching for Paragraph Based Questions Waves.
At Case Study Questions there will given a Paragraph. In where some Important Questions will made on that respective Case Based Study. There will various types of marks will given 1 marks, 2 marks, 3 marks, 4 marks.
CBSE Case Study Questions Class 11 Physics Waves
Case Study – 1
When we speak, the sound moves outward from us, without any flow of air from one part of the medium to another. The disturbances produced in air are much less obvious and only our ears or a microphone can detect them. These patterns, which move without the actual physical transfer or flow of matter as a whole, are called waves. The most familiar type of waves such as waves on a string, water waves, sound waves, seismic waves, etc. is the so-called mechanical waves. These waves require a medium for propagation, they cannot propagate through vacuum. They involve oscillations of constituent particles and depend on the elastic properties of the medium. The electromagnetic waves that you will learn in Class XII are a different type of wave. Electromagnetic waves do not necessarily require a medium – they can travel through vacuum. Light, radio waves, X-rays, are all electromagnetic waves. We have seen that motion of mechanical waves involves oscillations of constituents of the medium. If the constituents of the medium oscillate perpendicular to the direction of wave propagation, we call the wave a transverse wave. If they oscillate along the direction of wave propagation, we call the wave a longitudinal wave. In transverse waves, the particle motion is normal to the direction of propagation of the wave. Therefore, as the wave propagates, each element of the medium undergoes a shearing strain. Transverse waves can, therefore, be propagated only in those media, which can sustain shearing stress, such as solids and not in fluids. Fluids, as well as, solids can sustain compressive strain; therefore, longitudinal waves can be propagated in all elastic media.
For example, in medium like steel, both transverse and longitudinal waves can propagate, while air can sustain only longitudinal waves. Answer the following.
1) Air can sustain
a) Transverse waves
b) longitudinal waves
c) both a and b
d) none of these
2) The electromagnetic waves can pass through
a) Solids only
b) Fluids only
c) Any medium even through vacuum
d) None of these
3) Define Transverse waves
4) Define longitudinal waves
5) Differentiate between Transverse waves and longitudinal waves
Answer key-1
1) b
2) c
3) If the constituents of the medium oscillate perpendicular to the direction of wave propagation, wave is called as transverse wave.
4) If oscillations of constituents of the medium are along the direction of wave propagation that is parallel to direction of propagation we call the wave a longitudinal wave.
5) Following are differentiation points
Sr No. | Transverse waves |
longitudinal waves |
1 | If the constituents of the medium oscillate perpendicular to the direction of wave propagation, wave is called as transverse wave | If oscillations of constituents of the medium are along the direction of wave propagation that is parallel to direction of propagation we call the wave a longitudinal wave. |
2 | Can passs trough solids only | Can pass through both solids and fluids |
3 | Example electromagnetic waves | Example sound wave |
Case Study – 2
What happens if a pulse or a wave meets a boundary? If the boundary is rigid, pulse travelling along a stretched string and being reflected by the boundary. Assuming there is no absorption of energy by the boundary, the reflected wave has the same shape as the incident pulse i.e. crest is reflected as crest and trough as trough but it suffers a phase change of π or 1800 on reflection. This is because the boundary is rigid and the disturbance must have zero displacement at all times at the boundary. By the principle of superposition, this is possible only if the reflected and incident waves differ by a phase of π, so that the resultant displacement is zero. This reasoning is based on boundary condition on a rigid wall. If on the other hand, the boundary point is not rigid but completely free to move (such as in the case of a string tied to a freely moving ring on a rod), the reflected pulse has the same phase and amplitude (assuming no energy dissipation) as the incident pulse. The net maximum displacement at the boundary is then twice the amplitude of each pulse. An example of non- rigid boundary is the open end of an organ pipe. To summaries, a travelling wave or pulse suffers a phase change of π on reflection at a rigid boundary and no phase change on reflection at an open boundary. We considered above reflection at one boundary. But there are familiar situations (a string fixed at either end or an air column in a pipe with either end closed) in which reflection takes place at two or more boundaries. In a string, for example, a wave travelling in one direction will get reflected at one end, which in turn will travel and get reflected from the other end. This will go on until there is a steady wave pattern set up on the string. Such wave patterns are called standing waves or stationary waves.
1) A travelling wave or pulse suffers a phase change of π on reflection at
a) a rigid boundary
b) open boundary
2) A travelling wave or pulse suffers no phase change on reflection at
a) a rigid boundary
b) open boundary
3) What are stationary waves?
4) Write a note on reflection of travelling wave from rigid boundary.
5) Write a note on reflection of travelling wave from open boundary.
Answer key – 2
1) a
2) b
3) A wave travelling in one direction will get reflected at one end, which in turn will travel and get reflected from the other end. This will go on until there is a steady wave pattern set up on the string. This wave remains steady in medium and does not travel further such wave patterns are called standing waves or stationary waves.
4) If the boundary is rigid, a pulse travelling along a stretched string and being reflected by the boundary. The reflected wave has the same shape as the incident pulse i.e. crest is reflected as crest and trough as trough but it suffers a phase change of π or 1800 on reflection. This is because the boundary is rigid and the disturbance must have zero displacement at all times at the boundary. By the principle of superposition, this is possible only if the reflected and incident waves differ by a phase of π, so that the resultant displacement is zero. This reasoning is based on boundary condition on a rigid wall.
5) If the boundary point is not rigid but completely free to move the reflected pulse has the same phase and amplitude (assuming no energy dissipation) as the incident pulse. The net maximum displacement at the boundary is then twice the amplitude of each pulse. An example of non- rigid boundary is the open end of an organ pipe
Case Study – 3
Beats is an interesting phenomenon arising from interference of waves. When two harmonic Sound waves of slightly different frequencies and comparable amplitude are heard at the same time, we hear a sound of similar frequency (the average of two close frequencies), but we hear something else also. We hear audibly distinct waxing and waning of the intensity of the sound, with a frequency equal to the difference in the two close frequencies. Beat frequency is given by
υ = υ1-υ2
Artists use this phenomenon often while tuning their instruments with each other. They go on tuning until their sensitive ears do not detect any beats.
Doppler Effect is a wave phenomenon, it holds not only for sound waves but also for electromagnetic waves. However, here we shall consider only sound waves. Doppler Effect is defined as increase or decrease in frequency of sound due to relative motion between source of sound and observer. Frequency increases when source and observer comes towards each other and frequency decreases when source and observer go away from each other .For sound the observed frequency n is given in terms of the source frequency v0 by
Here v is the speed of sound through the medium, is the velocity of observer relative to the medium, and is the source velocity relative to the medium. In using this formula, velocities in the direction OS should be treated as positive and those opposite to it should be taken to be negative. The change in frequency caused by a moving object due to Doppler Effect is used to measure their velocities in diverse areas such as military, medical science, astrophysics, etc. It is also used by police to check over-speeding of vehicles. A sound wave or electromagnetic wave of known frequency is sent towards a moving object. Some part of the wave is reflected from the object and its frequency is detected by the monitoring station. This change in frequency is called Doppler shift. It is used at airports to guide aircraft, and in the military to detect enemy aircraft. Astrophysicists use it to measure the velocities of stars. Doctors use it to study heart beats and blood flow in different parts of the body. Here they use ultrasonic waves, and in common practice, it is called sonography. Ultrasonic waves enter the body of the person, some of them are reflected back, and give information about motion of blood and pulsation of heart valves, as well as pulsation of the heart of the foetus. In the case of heart, the picture generated is called echocardiogram. Answer the following
1) Beats are heard after superposition of two waves with beat frequency
a) υ = υ1- υ2
b) υ = υ1+υ2
c) υ = (υ1- υ2)/2
d) None of these
2) When source and observer comes towards each other then frequency heard will
a) increase
b) decrease
c) remains same
d) None of these
3) Define beats
4) Define Doppler effect in sound
5) Note on applications of Doppler Effect in sound.
Answer key – 3
1) a
2) a
3) Beats is an interesting phenomenon arising from interference of waves. When two harmonic Sound waves of slightly different frequencies and comparable amplitude are heard at the same time, we hear audibly distinct waxing and waning of the intensity of the sound, with a frequency equal to the difference in the two close frequencies. Beat frequency is given by = υ = υ1- υ2
4) Doppler Effect is defined as increase or decrease in frequency of sound due to relative motion between source of sound and observer. Frequency increases when source and observer comes towards each other and frequency decreases when source and observer go away from each other .For sound the observed frequency n is given in terms of the source frequency v0 by
Here v is the speed of sound through the medium, is the velocity of observer relative to the medium, and is the source velocity relative to the medium.
5) The change in frequency caused by a moving object due to Doppler Effect
a) It is used to measure their velocities in diverse areas such as military, medical science, astrophysics, etc
b) It is also used by police to check over-speeding of vehicles.
c) A sound wave or electromagnetic wave of known frequency is sent towards a moving object. Some part of the wave is reflected from the object and its frequency is detected by the monitoring station. This change in frequency is called Doppler shift. It is used at airports to guide aircraft, and in the military to detect enemy aircraft.
d) Astrophysicists use it to measure the velocities of stars. Doctors use it to study heart beats and blood flow in different parts of the body.
e) Doctors use it to study heart beats and blood flow in different parts of the body. Here they use ultrasonic waves, and in common practice, it is called sonography. Ultrasonic waves enter the body of the person, some of them are reflected back, and give information about motion of blood and pulsation of heart valves, as well as pulsation of the heart of the foetus. In the case of heart, the picture generated is called echocardiogram.
Class 11 Physics Waves