Characteristics of Light

 Identify the components of the electromagnetic spectrum.  Calculate the frequency or wavelength of electromagnetic radiation.  Recognize that light has a finite speed.  Describe how the brightness of a light source is affected by distance.

 An electromagnetic wave is a wave that consists of oscillating electric and magnetic fields, which radiate outward from the source at the speed of light.  Light is a form of electromagnetic radiation.  The electromagnetic spectrum includes more than visible light.

 What is the difference between an electromagnetic wave and a mechanical wave? Example?

 Which waves have the highest frequency? Shortest?  Which Waves have the Longest Wavelength? Shortest Wavelength?

 Electromagnetic waves vary depending on frequency and wavelength.  All electromagnetic waves move at the speed of light. The speed of light, c, equals c = 3.00  10 8 m/s  Wave Speed Equation c = f speed of light = frequency  wavelength

 Waves can be approximated as rays. This approach to analyzing waves is called Huygens’ principle.  Lines drawn tangent to the crest (or trough) of a wave are called wave fronts.  In the ray approximation, lines, called rays, are drawn perpendicular to the wave front.

 Illuminance decreases as the square of the distance from the source.  The rate at which light is emitted from a source is called the luminous flux and is measured in lumens (lm).

The speed of light, c, is constant in a vacuum. Light can be: REFLECTED ABSORBED REFRACTED Light is an electromagnetic wave in that it has wave like properties which can be influenced by electric and magnetic fields.

Law of Reflection Law of Reflection the angle of incidence is equal to the angle of reflection

Law of Reflection Law of Reflection

Reflection: Image Formation by a Plane Mirror What you see when you look into a plane (flat) mirror is an image, which appears to be behind the mirror.

Refraction occurs when a wave is passing from one MEDIUM into another. It is a “boundary” phenomenon. Suppose your car is traveling on concrete and then moves into the grass. What happens to your velocity? IT CHANGES! Refraction Fact #1: As light goes from one medium to another, the velocity CHANGES!.

Suppose you decide to go spear fishing, but unfortunately you aren’t having much luck catching any fish. Refraction Fact #2: As light goes from one medium to another, the path CHANGES!

As the speed changes, one wheel is traveling at a different speed than the other… so the car swerves… or “refracts.”.

Light (and all waves) behave the same as the car..

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If the car approaches the boundary along the normal, there is still a change in speed, but there is no refraction..

 1.99 x 10 8 m/s n = c/v 1.51 = 3.0 x 10 8 / v v = 1.99 x 10 8 m/s

Speed of Sound Sound can travel through any kind of matter, but not through a vacuum. The speed of sound is different in different materials; in general, it is slowest in gases, faster in liquids, and fastest in solids. The speed depends somewhat on temperature, especially for gases.

What do you notice?

 Problem: The frequency of an oboe’s A is 440 Hz. What is the period of this note? What is the wavelength? Assume a speed of sound in air of 340 m/s. f = 440 Hz T = ? λ = ? v = 340 m/s T= 1/f T=1/440T= s V= λf340= λ440 λ=.773m

Energy Transported by Waves The intensity is also proportional to the square of the amplitude:

Energy Transported by Waves If a wave is able to spread out three-dimensionally from its source, and the medium is uniform, the wave is spherical. Just from geometrical considerations, as long as the power output is constant, we see:

Doppler Effect The Doppler effect occurs when there is relative motion between the source of sound and an observer. This means either the source or the observer or both can be moving.

Stationary source Moving source Supersonic source Animations courtesy of Dr. Dan Russell, Kettering University

Doppler Effect A source moving toward an observer has a higher frequency and shorter wavelength When a source is moving away from an observer, a lower frequency is observed. The Doppler effect is seen in all types of waves: light, sound, radio waves.