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Chapter 7 Oscillation Physics 11th Class Punjab Short Questions

Question No. 1 - Describe free vibrations.

Answer No. 1 - A Body is said to be executing free vibrations when it oscillates without the interference of an external force.

Question No. 2 - Define. (a) Resonance (b) Damping

Answer No. 2 - Resonance: When the frequency of the applied force is equal to the natural frequency of simple harmonic oscillator, the periodic amplitude of the motion may become extraordinary large. This phenomenon is called resonance.
Damping: The oscillations in which the amplitude decreases steadily with time are called damped oscillations and this phenomenon is called damping.

Question No. 3 - What is sharpness of resonance?

Answer No. 3 - The amplitude s well as its sharpness< both depend upon the damping. Smaller the damping, greater will be the amplitude and more sharp will be the resonance.

Question No. 4 - Write one advantage and one disadvantage of resonance.

Answer No. 4 - Advantage: A swing is a good example of mechanical resonance. If a series of regular pushes are given to the swing , its motion can be built up enormously .
Disadvantages: The rhythmic march of column of soldiers on a bridge of long span might set up oscillations of dangerously large amplitude in the bridge structure. Bridge can be collapsed due to violent resonance oscillations. They are advised break their steps.

Question No. 5 - Explain relation between total energy, potential energy and kinetic energy for a body in simple harmonic motion.

Answer No. 5 - When the K.E of the mass is maximum, the p.e of the spring is zero. Conversely, when the P.E of the spring is maximum, the K.E of the mass is zero. The interchange occurs continuously from one form to the other but the total energy remains conserved.

Question No. 6 - Why the amplitude of lead bob is greater than pith ball as the bobs having equal size and length set into vibration?

Answer No. 6 - It is because the mass of lead bob is much greater than the very light pith ball, so lead bob can travel to greater extent in air against the resistivity and retarding forces. Lead bob has greater inertia.

Question No. 7 - Define vibratory motion.

Answer No. 7 - The to and fro motion of a body about a fixed point is called the vibratory or oscillatory motion.

Question No. 8 - Explain free and forced oscillations.

Answer No. 8 - Free oscillations: A body is said to be executing free vibrations when it oscillates without the interference of an external force.

Forced oscillations: If an oscillating system is subjected to an external periodic force, then forced vibrations will take place.
1. The vibrations of a factory floor caused by the
running of heavy machinery is an example of forced
vibrations.
2. The mass of a vibrating pendulum is struck repeatedly,
the forced vibration are produced.

Question No. 9 - Described some common phenomena in which resonance plays an important role.

Answer No. 9 - Tuning of a radio: It is a good example of electrical resonance. For tuning we turn the knob of a radio which changes the natural frequency of electrical circuit of receiver until it becomes equal to the frequency of the transmitter. So resonance is produced and energy absorption is maximum. Hence a station is tuned and we can hear the transmission of desired station .
Microwave oven: The waves produced in this type of oven have a wavelength of 12cm at a frequency of 2450 Mhz at this frequency the waves are absorbed due to resonance by water and fat molecules in the food resulting in efficient and evenly heating and cooking of food.

Question No. 10 - Briefly give two phenomena in which resonance plays an important role.

Answer No. 10 - 1) Tuning a radio, we turn the knob to make the natural frequency of the electric circuit of receiver equal to the transmission frequency of the radio station. When the two frequencies match, energy absorption is maximum and this is the only station we hear.
2) Food can be easily cooked in a microwave oven. The waves produced in this type of oven have a frequency of 2450 Mhz. At this frequency the waves are absorbed due to resonance by water and fat molecules in the food.

Question No. 11 - The amplitude of simple pendulum should be small, Why?

Answer No. 11 - If amplitude of simple pendulum is large then force of air friction changes its time period, Therefore amplitude should be kept small.

Question No. 12 - How a particular station is tuned in radio?

Answer No. 12 - Tuning of a radio is the best example of electrical resonance. When we turn the knob of a radio, to tune a station , we are changing the natural frequency of electrical circuit of receiver, to make it equal to the transmission frequency of the radio station. When the two frequencies match, energy absorption is maximum and this is the only station we hear.

Question No. 13 - How cooking of food is possible in micro-wave oven?

Answer No. 13 - Food can be easily cooked in a microwave oven. The waves produced in this type of oven have a frequency of 2450 MHz. At this frequency the waves are absorbed due to resonance by water and fat molecules in the food.

Question No. 14 - What do you understand by forced vibration? Explain with examples.

Answer No. 14 - If an oscillation system is subjected to an external periodic force, then force vibrations will take place.
1. The vibrations of a factory floor caused by the running
of heavy machinery is a example of forced vibrations.
2. The mass of a vibrating pendulum is struck repeatedly,
the forced vibrations are produced.

Question No. 15 - What is driven harmonic oscillator? Give example.

Answer No. 15 - A Physical system under going forced vibrations is called driven harmonic oscillator.
An example of forced vibration is loud music produced by sounding wooden boards of strings instruments.

Question No. 16 - What is the total distance traveled by an object moving with SHM in a time equal to its period, if its amplitude is A?

Answer No. 16 - The total distance traveled by an object moving with SHM in its time period is 4A, where A is amplitude of vibration.

Question No. 17 - Define driven harmonic oscillator and damped oscillations.

Answer No. 17 - Damped Oscillations: The Oscillations in which the amplitude decreases steadily with time are called damped oscillations.

Driven harmonic oscillator: The physical system undergoing forced vibrations is known as driven harmonic oscillator.

Question No. 18 - Describe some common phenomena in which resonance plays an important role.

Answer No. 18 - 1. A swing is a good example of mechanical resonance.
2. Tuning of the radio is the best example of electrical
resonance.
3. Another good example of resonance is the heating and
cooking of food very efficiently and evenly by microwave
oven.

Question No. 19 - Define resonance.Write its one example.

Answer No. 19 - When the frequency of the applied force is equal to the natural frequency of simple harmonic oscillator, the periodic amplitude of the motion may become extraordinary large. This phenomenon is called resonance.
1. A swing is a good example of mechanical resonance.
2. Turning a radio is the example of electrical resonance.

Question No. 20 - What are damped oscillations?

Answer No. 20 - The oscillations in which the amplitude decreases steadily with time are called damped oscillations.
Fro example
1. The shock absorbed of a car.
2. Motion of any microscopic system.

Question No. 21 - Differentiate between damped oscillation and undamped oscillations.

Answer No. 21 - Damped Oscillation: The oscillations in which the amplitude decreases steadily with time are called damped oscillations.
For Example, shock absorber of a car and motion of any microscopic system.
Undamped Oscillations: The oscillations in which the amplitude remains same with time are called undamped oscillations. For Example, oscillations in an ideal simple pendulum.

Question No. 22 - What is driven harmonic oscillator?

Answer No. 22 - The physical system undergoing forced vibrations is known as driven harmonic oscillator.

Question No. 23 - What is slinky spring?

Answer No. 23 - A large and loose spring coil is called slinky-spring. It can be used to demonstrate the effect of the motion of the source in generating waves in a medium.

Question No. 24 - What are damped oscillations? Give some of its applications.

Answer No. 24 - The oscillations in which the amplitude decreases steadily with time are called damped oscillations
For example
1. The shock absorber of a car.
2. Motion of any microscopic system.

Question No. 25 - Can we realize an ideal simple pendulum?

Answer No. 25 - No, we can't realize an ideal simple pendulum. Because an ideal simple pendulum should consist of a heavy but small metallic bob suspended from a friction-less rigid support by means of long, weightless and in-extensible string.

Question No. 26 - Define Simple Harmonic Oscillator and driven harmonic oscillator.

Answer No. 26 - The oscillator motion taking place under the action of restoring force is known as simple harmonic motion.A body such as simple pendulum , executing SHM is called simple harmonic oscillator.
A physical system undergoing forced vibrations is know as driven harmonic oscillator.

Question No. 27 - Define frequency and give its unit.

Answer No. 27 - Number of vibrations per second is called frequency.
Its S.I unit is Hz.

Question No. 28 - Why soldiers are advised to break their steps when marching on a bridge?

Answer No. 28 - The column of soldiers, while marching on a bridge of long span is advised to break their steps. Because their rhythmic march might set up oscillation of dangerously large amplitude in the bridge structure.

Question No. 29 - How the phenomenon of resonance is produced?

Answer No. 29 - When the frequency of the applied force is equal to the natural frequency of simple harmonic oscillator, the periodic amplitude of the motion may become extraordinary large. This phenomenon is called resonance.
1. A swing is a good example of mechanical resonance.
2. Tuning a radio is the example of electrical resonance.

Question No. 30 - If a heavy and light masses of same size are set into vibration, which of them will stop first?

Answer No. 30 - Light mass will stop first.
The damping effect for the light mass due to air resistance is much greater than the heavy mass. Therefore, it will stop first.

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