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Unit Two

Waves

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Chapter Seven

Vibrations & Waves

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Objectives

  1. Definition of Vibrations
  1. Characteristics of Vibrations
  1. Types of propagation of Waves
  1. Characteristics of a Wave
  1. Definition of Waves
  1. Nature of Waves.

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  1. Definition of Vibrations

What is a vibration??

Vibration or Oscillation: is regular to – and – fro motion of a vibrating object between two extreme positions.

See the following

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  1. Definition of Vibrations

What is a vibration??

Vibration: is repetitive motion of a moving body about its equilibrium position.

See the following

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  1. Definition of Vibrations

vibrations of a plastic ruler:

What is a vibration??

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Vibration: is repetitive motion of a moving body about its equilibrium position.

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  1. Characteristic of Vibrations
  1. Period (T ): the time needed for an body to make one vibration. T=1/f. Expressed in seconds (S).
  2. Frequency (f): is the number of completed cycle per time. f = N/t and for one cycle f = 1/T. expressed in 1/seconds (S-1) =Hertz (Hz).
  3. Amplitude (A): is the maximum displacement of the vibration from the equilibrium position.

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  1. Characteristic of Vibrations

A mass suspended by a spring, describes a line segment of length 20cm and makes 40 oscillations in 20 s. calculate:

  1. The amplitude of oscillation.
  2. The frequency.
  3. The period of the motion of the mass.

Example 1:

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  1. Characteristic of Vibrations
  1. Calculate the amplitude of oscillation.

The amplitude (A) is equal to half of the described segment.

A = 20cm/2 → A = 10cm.

Solution of Example 1:

Given:

  • Length= 20cm
  • 40 oscillations
  • in 20 s.

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  1. Characteristic of Vibrations

 

Solution of Example 1:

Given:

  • Length= 20cm
  • 40 oscillations
  • in 20 s.

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  1. Characteristic of Vibrations

 

Solution of Example 1:

Given:

  • Length= 20cm
  • N = 40 oscillations.
  • In t= 20 s.
  • A= 10cm.
  • f = 2Hz (proved).

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  1. Definition of Waves:

What is a Waves??

  • A wave is a disturbance that carries energy from place to place.

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  • A wave does NOT carry matter with it! It just moves the matter as it goes through it.

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  1. Characteristic of a Wave
  1. Frequency (f) : is the number of completed cycle per time. f = N/t and for one cycle f=1/T.
  2. Period (T): is the time needed for an object to make one vibration.: T = 1/f.

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  1. Characteristic of a Wave
  1. Amplitude (A): is the maximum displacement of the wave measured from the equilibrium position.
  2. Wavelength (λ): is the traveled distance of a wave. It is the distance between Crest – Crest or between Trough – Trough.

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  1. Characteristic of a Wave

 

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  1. Characteristic of a wave

A water wave in a pool of wavelength 0.8m and its speed of propagation is 0.2m/s. calculate:

  1. The period of the wave.
  2. The frequency of the wave.

Example 2:

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  1. Characteristic of a wave

 

Solution of Example 2:

Given:

  • λ = 0.8m.
  • V = 0.2m/s.

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  1. Characteristic of a wave

 

Solution of Example 2:

Given:

  • λ = 0.8m.
  • V = 0.2m/s.
  • T = 4s. (proved)

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  1. Types of Propagation of waves:
  1. Transverse wave:

When the particles of the medium are displaced perpendicular to the direction of propagation of the wave.

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  1. Types of Propagation of waves:
  1. Longitudinal (Compressional) wave:

When the particles of the medium are displaced parallel to the direction of propagation of the wave.

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  1. Nature of waves
  1. Mechanical wave:
  2. A wave that needs a material medium to travel.
  3. It can’t propagate in vacuum.
  4. Ex: water wave, sound wave...

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  1. Nature of waves
  1. Electromagnetic wave:
  2. wave that doesn't require medium to propagate.
  3. can propagate in material medium or in vacuum.
  4. Example: light wave.

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  1. Table of Summary

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Grade 10 Solving problems physics

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Water waves strikes the seawall. Eight waves hit the seawall in 5 s. The distance between two successive troughs is 9 m. The height of the waveform trough to crest is 1.5 m.

Exercise 1:

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Grade 10 Solving problems physics

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  1. How many complete waves are indicated in the sketch?
  2. Calculate the amplitude of the wave.
  3. Show that the period of the wave is 0.625 s.
  4. Calculate the frequency of the waves.
  5. Calculate the velocity of the waves.

Exercise 1:

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Grade 10 Solving problems physics

  1. How many complete waves are indicated?

We have 3 complete waves are shown.

solution of Exercise 1:

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Grade 10 Solving problems physics

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  1. Calculate the amplitude of the wave.

We are given the height, the amplitude is half the height: A= 0,75 m.

Solution of Exercise 1:

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Grade 10 Solving problems physics

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Solution of Exercise 1:

Given:

  • N=8 waves
  • t = in 5s.
  • trough-trough = 9m.
  • trough – crest=1.5 m.

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Grade 10 Solving problems physics

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Solution of Exercise 1:

Given:

  • N=8 waves
  • t = in 5s.
  • trough-trough = 9m.
  • trough – crest=1.5 m
  • f = 1.6Hz(proved)
  • T = 0.625s (proved).

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Grade 10 Solving problems physics

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A child dips a ruler inside pool. Plane waves are produced and propagate at a speed V=8 cm/sec. The sketch of the obtained wave is shown.

Exercise 2:

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Grade 10 Solving problems physics

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  1. Find the wavelength and the amplitude of the wave.
  2. Determine the frequency and the period of this wave.
  3. What distance this wave will travel in 5 sec?
  4. Is this wave transverse, longitudinal, mechanical or electromagnetic? Why?

Exercise 2:

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Grade 10 Solving problems physics

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  1. Find the wavelength and the amplitude of the wave.

Solution of Exercise 2:

 

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Grade 10 Solving problems physics

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Solution of Exercise 2:

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Grade 10 Solving problems physics

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Solution of Exercise 2:

 

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Grade 10 Solving problems physics

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Solution of Exercise 2:

  1. Is this wave transverse or longitudinal; mechanical or electromagnetic? Why?

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Transverse: because the particles of the medium are displaced perpendicular to the direction of propagation of the wave.

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Mechanical: because the wave propagate through medium (water).

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Quiz in physics (5 points)

Chapter 17: Waves and vibrations

Time: 10 min

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Grade 10 Quiz in Physics Time: 20min

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Exercise 1: (5 points) Characteristics of a wave

The figure below is a section of a wave that is drawn for oscillation of a water wave.

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Grade 10 Quiz in Physics Time: 20min

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Exercise 1: (5 points) Characteristics of a wave

  1. What is the value of the wavelength? (0.5 point).
  2. What is the value of the amplitude? (0.5 point).
  3. It takes 0.2sec to complete 2cycles. Deduce the T, f, and V of this wave. (1.5 point).
  4. Is this wave transverse or longitudinal? Why? (1 point).
  5. Draw any wave and label its amplitude, period, wavelength, crest and trough. (1.5 points).

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Grade 10 Quiz in Physics Time: 20min

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Grade 10 Quiz in Physics Time: 20min

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  1. What is the value of the amplitude?

amplitude: is the maximum distance from the equilibrium. A=1cm. (0.5 point).

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Grade 10 Quiz in Physics Time: 20min

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Grade 10 Quiz in Physics Time: 20min

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  1. Is this wave transverse or longitudinal? Why?

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This wave is transverse, because the particles of the medium are displaced perpendicular to the direction of propagation of the wave. (0.5 point).

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Grade 10 Quiz in Physics Time: 20min

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  1. Draw any wave and label on it the characteristics of a wave.. (1.5 points).

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End of Chapter 7