1.5 Analysing Interference of Waves - PowerPoint PPT Presentation

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1.5 Analysing Interference of Waves

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1.5 Analysing Interference ... State the principle of superposition Explain the interference o waves Draw and interpret interference patterns Solve problems ... – PowerPoint PPT presentation

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Title: 1.5 Analysing Interference of Waves


1
WAVES
  • 1.5 Analysing Interference of Waves

2
LEARNING OUTCOMES
  • At the end of the lesson, student is able to
  • State the principle of superposition
  • Explain the interference o waves
  • Draw and interpret interference patterns
  • Solve problems using

3
  • Principle of superposition
  • When two or more waves pass through each other,
    the net displacement at a given point is equal to
    the vector sum of the displacement of the
    individual waves.

4
  • Interference is a phenomenon in which waves from
    two coherent sources passing the same point
    reinforce or cancel each other.
  • Coherent sources are sources that produce waves
    having
  • The same frequency
  • A constant phase difference.
  • There are two types of interference, namely
    constructive interference and destructive
    interference.
  • Constructive interference occurs when a crest
    meets another crest or a trough meets another
    trough.
  • Destructive interference occurs when a crest
    meets a trough.

5
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6
INTERFERENCE OF WATER WAVES
7
  • Along line A1, bright spots are found alternating
    with dark spots.
  • At a bright spot, two crests superimpose
    constructively to produce a higher crest.
  • At a dark spot, two trough superimpose
    constructively to produce a deeper trough.
  • Line A1 is called an antinodal line. Constructive
    interference occurs along an antinodal line.

8
  • Along line N1, uniform colour is observed. The
    water is calm along line N1
  • Crests superimpose with trough, thus destructive
    interference occur.
  • Line N1 is called an nodal line.

9
  • x distance between two successive antinodal
    lines(or nodal lines)
  • a distance between the two coherent sources of
    waves
  • D distance from each source of waves to line PQ
    where x is measured

10
EXERCISE
  • Two coherant waves are produced in a ripple tank
    by dippers that are placed 5.0 cm from each
    other. At a distance of 20.0 cm from the dippers,
    the separation between adjacent antinodal lines
    is 3.0 cm. calculate the wavelength of the waves.
  • ANSWER 0.75 cm

11
INTERFERENCE OF SOUND WAVES
12
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13
  • (a) a loud sound is detected at the position
    where the sound waves from the loudspeakers
    interfere constructively.
  • (b) a soft sound is detected at the position
    where the waves from the loudspeakers interfere
    destructively.
  • For interference of sound waves, the equation is
    given also as

14
EXERCISE
  • Two loudspeakers connected to an audio signal
    generator were placed 1.2 m from each other. A
    student who was walking along a line 3.0 m in
    front of the loudspeakers could hear alternating
    loud and soft sounds, the distance between
    adjacent loud and soft sounds is 0.85 m. What is
    the wavelength of the sound.
  • ANSWER 0.68 m

15
INTERFERENCE OF LIGHT WAVES
16
  • Interference of light waves can be studied using
    Youngs double slit.
  • When a beam of monochromatic light passes through
    the double slit, interference of light produces a
    pattern consisting of bright and dark fringes on
    the screen.

17
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18
  • The light that passes through each slit is
    diffracted. The two diffracted beams of light
    superimpose.
  • (a) at the bright fringe, the light waves from
    each slit interfere constructively.
  • (b) at the dark fringe, the light waves from
    each slit interfere destructively.
  • For interference of sound waves, the equation is
    given also as

19
EXERCISE
  • The figure below shows the interference pattern
    formed by red laser light.
  • Calculate the value of y.
  • ANSWER 8.16 mm
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