L03 - Reflection, Refraction, Diffraction - Cambie Roboticscambierobotics.com/HTML/Physics/L03 -...

ObjectivesRecognize and describe the properties of:

� Wave reflection

� Wave refraction

� Wave diffraction� Wave diffraction

Each of these is a Big IdeaBig Idea

Wave Reflection

Where have you experienced waves reflecting?

� Echoes

� Radio wavesRadio waves

Wave Reflection

� Waves at right angles

�Waves at oblique angles

�Waves at oblique angles

Wave Reflection

Angle of Incidence

Incident Ray

Angle of Incidence

Angle of

Reflection

Reflected Ray

Wave Refraction

Where do waves move from one medium to another?

� Sound from cold air to warm air� Sound from cold air to warm air

� Light from space to air

� Light from air to water

Wave Refraction� Water passes from deep water to shallow water -

Wavelength shortens

Wave Refraction

When waves move from one medium to another, two things happen:

1. The wave velocity changes1. The wave velocity changes

2. The wave direction changes

Wave Refraction

� Recall the universal wave equation:v = f * λ

In Medium 1 - f1=v1/λ1In Medium 1 - f1=v1/λ1

In Medium 2 -

� No matter what the medium the frequency doesn’t change:

f1 = f2

� Therefore we get:v1/λ1 = v2/λ2

Wave RefractionSpeed of Sound:

� Sound wave speed changes depending on air temperature

v = 331m/s + (0.59 * T)vSOUND = 331m/s + (0.59 * T)vSOUND ~ 330m/s

� Does sound move faster or slower in cold air?

Wave Refraction� Oblique waves bend

towards the normal when entering slower medium

Normal

Normal

� Oblique waves bend away from the normal when entering faster medium

� Oblique waves bend away from the normal when entering faster medium

Wave RefractionWhen waves enter shallow water (lower speed medium)

they bend towards the normal (become more parallel to shore)

Wave Diffraction

Wave Diffraction

Wave Diffraction� Shorter incident

wavelengths are diffracted less

� Longer incident wavelengths are diffracted more

� Longer incident wavelengths are diffracted more

Wave Diffraction� Waves passing through smaller openings are diffracted more

� Waves passing through smaller openings are diffracted more

� Waves passing through larger openings are diffracted less

diffracted morediffracted more

Wave Diffraction

Short wavelengths

diffract less

around an object

Short wavelengths

diffract less

around an object

Long wavelengths

diffract more

around an object

Long wavelengths

diffract more

around an object

Summary� Incident/reflected rays are perpendicular to wavefronts� Angle between incident ray & normal = angle of incidence� Angle between reflected ray & normal = angle of reflection� Angle of incidence = angle of reflection� Waves refract when traveling from 1 medium to another� Waves refract when traveling from 1 medium to another� v1/λ1=v2/λ2� Oblique incident rays bend towards normal when entering a

slower medium� As wavelengths become longer they are diffracted more� As an opening becomes larger, waves passing through diffract

less� Particles do not bend around corners, but waves do

Homework� Reflection, Refraction, and Diffraction

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