# 1st Year Physics Chapter 7 Ossilation Notes pdf - 11th class

Here we have published the 1st Year Physics Chapter 7 Oscillation Notes pdf download or read online the notes of chapter 7 11th class physics oscillation.

Q. Define the following terms relation to SHM.
Wave form of SHM Instantaneous displacement Amplitude Vibration
• Time period
•  Frequency
•  Angular Frequency

Wave form of SHM
The curve representing the Venetian displacement with time called wave form of SHM
Explanation
Consider a mass spring system with vertical arrangement in such a way that pen attached with mass m from the trace on the strip of paper moving at constant speed from right to let So it provides a time scale on the strip The sine curve is obtained which shows the vanation of displacement with time.
It is called wave form of SHM
The point A C and E show its mean position while B and represent the extreme position
Instantaneous displacement
The shortest distance of the vibrating body at any instant from its mean position is called instantaneous displacement.It is usually denoted by x The value of instantaneous displacement is zero at mean position while has maximum value at the extreme position
Amplitude (x)
The maximum value of displacement of the vibrating body on either sides from its mean position is called amplitude it is denote by A
Vibration
On complete round trip of a body about its mean position is called one vibration Explanation
The motion of body from mean position to upper extreme position, from upper extreme position to lower extreme position and back to its mean position is called one vibration.
Time period
The time required to complete one vibration is called time period It is represented by T. Its unit is second
Frequency
The number of vibrations completed in one second by the body is called frequency It is the reciprocal of the time period is represented by The unit of frequency is hertz or vibration/sec on cycles/sec

#### Magnetic Resonance Imaging

Magnetic Resonance Imaging, or MRI s a method of imaging the interior of structures noninvasively An MRI device consists of a magnet, magnetic gradient coils an RF (radio frequency transmitter and receiver, and a computer that controls the acquisition of signals and computes the MR images.
The full name, Nuclear Magnetic Resonance Imaging usually shortened to MRI, describes the technique If an atomic Nucleus is exposed to a static Magnetic field, it Resonates when a varying electromagnetic field is applied at the proper frequency An Image is computed from the resonance signals of which the frequency and phase (timing) contain space information
MRI is important because it is noninvasive, safe and yields information that cannot be obtained with any other techniques Its most common use by far is in diagnostic medicine but MRI has other applications particularly in the oil and food industries
Collapse of suspended bridge
On a big span bridge the soldiers crossing the bridge are ordered to break their steps if the frequency of steps coincides with natural frequency of the bridge Then there is chance to collapse the bridge due to resonance
Turning of radio is a good example of electrical resonance. To tune a radio, We turn the knob of a radio It changes the natural frequency of electrical circuit of receiver until it becomes equal to the frequency of transmitter Now the resonance is produced and energy absorption is maximum Hence a station is tuned
Cooking by microwave oven
Resonance plays an important role in heating and cooking food by microwave oven The microwaves produce by oven are absorbed due to resonance by water and fats molecules in the food
This increases the internal energy of the molecules They get heat up and so food is cooked
Note The wave length of the microwaves produced in this type of oven is 12 cm and frequency is 2450 MHz
Q. What are damped and undammed oscillations? What is damping?
Damped Oscillations
Oscillations in which amplitude decreases with time due to energy dissipation are called damped Oscillations
Explanation
The amplitude of the oscillatory body gradually becomes smaller and smaller because of friction and air resistance. As energy of the oscillator is used up in doing work against the resistive forces, that is why the amplitude decreases with time till it becomes zero Applications
An application of damped oscillation is the shock absorber of a car which provides a damping force to stop the excessive oscillations
Damping
Damping is the process by which energy is lost by the oscillatory system.
Undamped oscillations
Oscillations in which the amplitude remains same with time is called undamped oscillations In undamped oscillations energy is not dissipated from the oscillatory system Example
Oscillations of an ideal simple pendulum is an example of damped oscillations
Sharpness of Resonance
The amplitude of vibration of a body increase when the damping is small Thus, the presence of damping prevents the amplitude from becoming sufficiently large The amplitude decreases rapidly at a frequency slightly different from resonance frequency The amplitude as well as sharpness depends upon damping A heavily damped system has fairly flat resonance curve
Example to see the effect of damping Attach a pendulum having very light mass such a pith ball and another of same length with a heavy mass of equal size such as lead ball.
Set them into vibration by third pendulum of equal length and attached to the same rod It is observed that the amplitude of the heavy ball is much greater than the light ball So the sharpness of the resonance curve of resonating system depends on energy loss due to friction.

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