Chapter Unit - 3 : Sound - Different Kinds of Vibrations and Characteristics - Frank Solutions for Class 10 Physics ICSE
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Chapter 3 - Sound - Different Kinds of Vibrations and Characteristics Excercise 159
E.g.1 all stringed instruments are provided with sound box (or sound chamber). This box is so constructed that the column of of air inside it, has a natural frequency which is the same as that of the strings stretched on it, so that when the strings are made to vibrate, the air column inside the box is set to forced vibrations. Since the sound box has a large area, it sets a large volume of air into vibration of the same frequency as that of the string. So, due to resonance, a loud sound is produced.
E.g.2 Radio and TV receivers have electronic circuits which produce electrical vibrations, the frequency of which can be changed by changing the values of the electrical components of that circuit. When we want to tune a radio or TV receiver, we merely adjust the values of the electronic components to produce vibrations of frequency equal to that of the incoming radio waves which we want to receive. When the two frequencies match, due to resonance, the energy or signal of that particular frequency is received from the incoming waves. The signal is then amplified in the receiver set.
(i) Which of the diagram shows the principle note?
(ii) Which has the frequency four times that of the first?
(iii) What is the ratio of the frequency of the vibration in (a) and (b)?
(ii) Diagram (c) has the frequency four times that of first.
(iii) The ratio of frequency of the vibration in (a) and (b) is 1:2.
1. When the stem of a vibrating tuning fork is pressed against the top of a table, the tuning fork forces the table top to vibrate with its own frequency. The vibrations produced in the table top are forced vibrations.
2. When a guitar is played, the vibrations produced by the strings of the guitar are the forced vibrations.
In case of resonance, the externally applied periodic force has the same frequency as the natural frequency of oscillation of the given oscillatory system.
1. Frequency of the fundamental note of a stretched string is inversely proportional to the length of the vibrating string.
2. Frequency is directly proportional to the square root of the tension of the string.
3. Frequency is inversely proportional to the square root of linear density. That is, mass per unit length of the material of the string. Thinner is the wire, higher is the frequency.
1. By increasing the tension in the string.
2. By decreasing the length of the string.
(i) Describe the observations with the tubes P, R and S.
(ii) Give the reason for your observation in each case.
(iii) State the principle illustrated by the above experiment.
(ii) Resonance occurs with the air column in tubes Q and S whereas no resonance occurs in the air columns of tubes P and R. The frequency of vibrations of air column in the tube S is thrice the frequency of vibrations of air column in the tube Q, while the frequency of vibrations of air column in tubes P and R is neither equal to nor an integer multiple of frequency of vibrations of air column in tube Q.
(iii) When the frequency of vibrations of air column is either equal to or an integer multiple of the frequency of the vibrating tuning fork, resonance occurs.
Chapter 3 - Sound - Different Kinds of Vibrations and Characteristics Excercise 160
The vibrating tuning fork A produces the forced vibrations in the air column of its sound box. These vibrations are of large amplitude because of large surface area of the air in the sound box and they are communicated to the sound box of the fork B. The air column of B starts vibrating with the frequency of fork A. Since the frequency of these vibrations is same as the natural frequency of the fork B, the fork B starts vibrating due to resonance.
(ii) The principle of 'resonance' is illustrated by this experiment.
Statement: When the frequency of the forced vibration is equal to the natural frequency of a body nearby or an integer multiple of it then the body vibrates with a large amplitude. This phenomenon is called resonance.
Reason: The vibrations produced in pendulum P are communicated to the other pendulums Q,R and S through the elastic string XX'. The pendulums Q and R are in the state of forced vibrations, while the pendulum S is in the state of resonance. This is because the natural period of pendulum S is equal to that of P (being of same length), and therefore resonance takes place. The pendulum S therefore vibrates with the amplitude of P and remains in phase with the pendulum A.
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