Nature Of Vibration Long Answer Type Questions
WBBSE Class 11 Nature of Vibration Q&A
Question 1. Why does an empty container emit a louder sound than a water-filled container when they are struck?
Answer:
When we strike the container, its wall vibrates. These vibrations produce forced vibrations in the air or water inside the container.
- If the container is filled with water, it becomes heavy and the amplitude of vibration becomes small. But if the container is empty, it is comparatively lighter and the amplitude of vibration is large.
- As the loudness of sound is proportional to the square of the amplitude of vibration, the empty container emits a louder sound.
Question 2. Why do buildings get demolished by earthquakes?
Answer:
Buildings get demolished by earthquakes
An earthquake induces forced vibration in the walls of buildings. For intense earthquakes, the amplitudes of the forced vibrations become very high, which in many cases cross the elastic limit of the constituent materials of the buildings. So many buildings get demolished.
Question 3. A vibrating tuning fork is held at the mouth of a cylindrical tube. The tube is dipped into water. It is found that when the level of water rises to a definite height, a sound of large intensity is heard. Explain the reason behind it.
Answer:
Given
A vibrating tuning fork is held at the mouth of a cylindrical tube. The tube is dipped into water. It is found that when the level of water rises to a definite height,
The empty cylindrical tube is filled with air. The vibrating tuning fork produces forced vibration in the air column of the tube. As a result of the forced vibration of the air column, an additional sound is produced.
- The frequency of the sound produced depends on the length of the air column. By dipping the tube into water, the length of the air column can be changed.
- So, when the level of water rises to a particular height, the frequency of the air column in the tube and that of the tuning fork become equal. Then resonance takes place and a sound of large intensity is heard.
Question 4. In the presence of a resonant body, the sound produced by a body Is intensified. Is the principle of conservation of energy violated here?
Answer:
The principle of conservation of energy is not violated here.
- Suppose, a tuning fork is set into vibration. The loudness of the sound produced is not very large. If the vibrating fork is held on a hollow wooden box, the sound is intensified. In this case, the air inside the box acts as a resonant body.
- But it is found that the sound of the tuning fork lasts for a long time in the first case. But in the second case, the sound of the tuning fork is short-lived. The total dissipation of energy in both cases is the same.
- In the first case, the rate of dissipation of energy is low but continues for a long time. But in the second case, the rate of dissipation of the same amount of energy is comparatively high, and therefore the sound dies down in a short time. It does not violate the principle of conservation of energy.
Short Answer Questions on Vibration for Class 11
Nature Of Vibration Conclusion
If the effect of forces other than the restoring force acting on a vibrating body is negligible, then its vibration is called free or natural vibration.
If resistive forces act on a vibrating body in addition to the restoring force, its amplitude gradually diminishes. After some time, the body comes to rest at its position of equilibrium. This type of vibration is called damped vibration. The resistive effect is called damping.
If an external periodic force is applied to a freely vibrating body, the body tries to maintain its vibrations at its own frequency; but after some time, the body begins to vibrate with the frequency of the applied periodic force. Such a vibration of a body is called a forced vibration.
When the frequency of the applied periodic force matches the natural frequency of a vibrating body, its amplitude rapidly increases to a large value. This phenomenon is called resonance.
Nature Of Vibration Very Short Answer Type Questions
Question 1.Under the influence of which force the oscillation of a pendulum gradually dies out?
Answer: Resistive force
Question 2. Which force acts on a body during its free vibration?
Answer: Restoring force
Question 3. Which force acts on a body that vibrates freely?
Answer: Only a restoring
Question 4. A man with a wristwatch falls freely from a tall building. Will the watch give the correct time?
Answer: Yes, independent of g
Question 5. Which quantity of vibration gradually decreases during damped vibration?
Answer: Amplitude
Question 6.If a resistive force acts on a vibrating body, then its amplitude of vibration gradually ________
Answer: Decreases
Vibration Characteristics: Short Answer Questions
Question 7. What phenomenon will occur if the frequency of free vibration of a vibrating body becomes equal to the frequency of an external periodic force?
Answer: Resonance
Question 8. Which characteristic of sound increases during resonance?
Answer: Intensity
Question 9. A special case of ______ vibration is resonance.
Answer: Forced
Question 10. Which type of vibration is the vibration of the diaphragm of a microphone during a speech?
Answer: Forced
Question 11. What kind of external force has to act on a vibrating body, to occur forced vibration?
Answer: Periodic
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Nature Of Vibration Assertion Reason Type Questions And Answers
Direction: These questions have statement 1 and statement 2. Of the four choices given below, choose the one that best describes the two statements.
- Statement 1 Is true, statement 2 is true; statement 2 Is a correct explanation for statement 1.
- Statement 1 is true, and statement 2 is true; statement 2 is not a correct explanation for statement 1.
- Statement 1 is true, statement 2 is false.
- Statement 1 is false, and statement 2 is true.
Question 1.
Statement 1: A vibrating body always moves to and fro about an equilibrium position.
Statement 2: Due to inertia of motion a vibrating body does not stop at its equilibrium position.
Answer: 2. Statement 1 is true, statement 2 is true; statement 2 is not a correct explanation for statement 1.
Question 2.
Statement 1: The sound gets amplified when a vibrating tuning fork is made to touch the surface of a table.
Statement 2: The dimension of the table is more than that of the tuning fork.
Answer: 1. Statement 1 Is true, statement 2 is true; statement 2 Is a correct explanation for statement 1.
WBBSE Class 11 Sample Questions on Vibrational Motion
Nature Of Vibration Match The Columns
Question 1.
Answer: 1. C, 2. D, 3. A, 4. B, D
Nature Of Vibration Integer Answer Type Questions
In this type, the answer to each of the questions is a single-digit integer ranging from 0 to 0.
1. The amplitudes of the first two oscillations of a damped pendulum are 9.0 cm and 3.0 cm respectively. What will be the amplitude (in cm) of the pendulum in its third oscillation?
Answer: 1
Question 2. After 50 complete oscillations a pendulum’s amplitude becomes 1/3 of its initial vibration. If its amplitude becomes \(\frac{1}{n^3}\) of its initial vibration after 150 complete oscillations, then find the value of n.
Answer: 3