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Unit Two

Waves

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Chapter 8

Reflection& Refraction Waves

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Objectives

1

Wave Fronts

2

Reflection of waves

3

Refraction of waves

4

Index of refraction

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Wave Fronts

Drop a stone in a pool of water. A set of circular ripples are produced.

The pattern of waves seen from above consist a circle called wave fronts.

These circles are equally spaced because the speed is constant.

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Reflection of Waves on Plane Surfaces

The incident Plane &parallel waves, are reflected as Plane & parallel waves.

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Reflection of Waves on Plane Surfaces

All doesn’t change because the wave still at the same medium.

During reflection of wave:

The speed (V).
The frequency(f).
The wavelength (λ).

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Refraction of Waves on a Plane Surface.

The distance between the two wave lines is the wavelength of the incident wave (λ₁).

The distance between the two wave lines is the wavelength of the refracted wave (λ₂).

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Refraction of Waves on a Plane Surface.

During Refraction:

The wave passes from one medium(1) to medium(2).
The frequency doesn’t change: f₁=f₂=f.

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Refraction of Waves on a Plane Surface.

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Refraction of Waves on a Plane Surface.

Refraction of water wave

General Rules:

1

Water waves travel fastest in deep water.

2

Water waves travel slower in shallow water.

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Refraction of Waves on a Plane Surface.

Case 1: From Deep to Shallow water

If water waves are passing from deep water into shallow water, they will slow down.
This decrease in speed will also be accompanied by a decrease in wavelength.
The frequency does not change with the change of medium.

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Refraction of Waves on a Plane Surface.

Case 1: From Deep to Shallow water

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Refraction of Waves on a Plane Surface.

Case 2: From Shallow to Deep water

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Refraction of Waves on a Plane Surface.

Case 2: From Shallow to Deep water

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Characteristic of Vibrations

A light wave passes from air to benzene.

Calculate the index of refraction of benzene knowing that speed of light in benzene is V= 200 × 10⁶ km/s. given C = 3 × 10⁸ m/s.

Example 1:

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Characteristic of Vibrations

Calculate the index (n) of refraction of benzene.

Solution of Example 1:

Given:

Vbenz =200 × 10⁶ km/s.
C = 3 × 10⁸ m/s.

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Index of refraction of medium.

Consider a wave passes from medium 1 ( air) to medium 2 ( water) :

to be used directly

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Index of refraction of medium.

The wavelength of a laser light in air is λ1=0.66μm.

Calculate the wavelength is (λ2) of this laser when it passes through a medium of glass of index n = 1.5.

Example 2:

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Index of refraction of medium.

Calculate the wavelength (λ2) of this laser when it passes through a medium of glass of index n = 1.5.

solution of Example 2:

Given:

λ1=0.66μm ( in air)
nglass = 1.5

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Grade 10 Solving problems physics

A plastic sheet is placed at the bottom of a ripple tank in order to produce two distinct mediums of propagation .

Exercise 1: Refraction of waves

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Grade 10 Solving problems physics

A plane parallel wave is created on the surface of water .The speed of wave in medium (1) is V₁=0.7m/s.

Using the information in the figure, determine the wavelength of the incident and refracted waves.
Calculate the speed of the refracted wave.

Exercise 1: Refraction of waves

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Grade 10 Solving problems physics

Using the figure, determine the wavelength of the incident and refracted waves.
For medium 1: 4λ1 = 20cm → λ1 = 20cm/ 4

→ λ1 =5cm

For medium 2: 4λ2 = 16cm → λ2 = 16cm/ 4

→ λ2 =4cm

Solution of Exercise 1:

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Grade 10 Solving problems physics

Solution of Exercise 1:

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Grade 10 Solving problems physics

A mechanical wave is produced on the surface of water. Doc-2 shows the displacement of water as a function of time.

Exercise 2: Propagation of waves

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Grade 10 Solving problems physics

The speed of propagation of the wave is v=7.5 cm/s.

Is this wave transverse or longitudinal? Justify.
Use Doc-2 to determine the period T and the amplitude (a) of the wave. Deduce it frequency f.
Calculate the wavelength λ of the wave.
The wave of doc-2 crosses from deep to shallow water. Its velocity of propagation becomes 5 cm/s.
What is the name of this physical phenomenon.
Calculate the new value of the wavelength.

Exercise 2: Propagation of waves

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Grade 10 Solving problems physics

Is this wave transverse or longitudinal? Justify.

Solution of Exercise 2:

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

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Grade 10 Solving problems physics

Use Doc-2 to determine the period T and the amplitude (a) of the wave. Deduce the frequency f.

Solution of Exercise 2:

T = 0.8s
a = 5cm
f = 1/T = 1/0.8

→ f= 1.25Hz or

f = N/t = 1.5/1.2

→ f=1.25Hz

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Grade 10 Solving problems physics

Calculate the wavelength λ of the wave.

Solution of Exercise 2:

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Grade 10 Solving problems physics

The wave of doc-2 crosses from deep to shallow water. Its velocity of propagation becomes 5 cm/s.
What is the name of this physical phenomenon.

Solution of Exercise 2:

The physical phenomenon is refraction of wave.

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Grade 10 Solving problems physics

wave crests. Refraction of plane waves is occurring as they cross a boundary. The wavelength of the incident waves is 2.0cm and their frequency is 6.0Hz.

Exercise 3:

The unlabeled lines represent successive

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Grade 10 Solving problems physics

Calculate the frequency of refracted waves.
Calculate the speed of incident waves.
Calculate the wavelength of refracted waves.
Calculate the speed of refracted waves.

Exercise 3:

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Grade 10 Solving problems physics

Solution of Exercise 3:

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Grade 10 Solving problems physics

Calculate the wavelength of refracted waves.

Solution of Exercise 3:

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Grade 10 Solving problems physics

Solution of Exercise 3:

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Quiz in physics (5 points)

Chapter 8: Reflection and refraction of Waves

Time: 10 min

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Grade 10 Quiz in Physics Time: 20min

Exercise 1: (5 points) Refraction of Light wave

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Grade 10 Quiz in Physics Time: 10min

Solution of Exercise 1:

What phenomenon takes place as the yellow light passes from water to flint? Does the yellow light keep its properties constant?

The phenomenon is refraction.

No; the yellow light does not keep its properties constant: the velocity and the wavelength will changes because the light passes from medium to another.

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Grade 10 Quiz in Physics Time: 20min

Solution of Exercise 1:

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Grade 10 Quiz in Physics Time: 20min

Solution of Exercise 1:

Draw a figure, representing the phenomenon occurred.

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Grade 10 Quiz in Physics Time: 20min

Solution of Exercise 1:

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Grade 10 Quiz in Physics Time: 20min

Solution of Exercise 1:

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Grade 10 Quiz in Physics Time: 20min

Solution of Exercise 1:

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Grade 10 Quiz in Physics Time: 20min

Solution of Exercise 1:

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End of Chapter 8