What is a light wave? Electromagnetic Radiation

Learning Targets Learning Target 9.8: I can identify and describe refraction. 
 Learning Target 9.9: I can apply the law of reflection. 
 Learning Target 9.10: I can order the wave types of the electromagnetic spectrum (including visible colors) according to frequency and wavelength. 


Electromagnetic Waves Light is an electromagnetic wave, which carries energy in the form of vibrating electric and magnetic fields. Unlike other waves, electromagnetic waves are capable of transmitting its energy through a vacuum (like empty space). All electromagnetic radiation travels through a vacuum at the same speed: c = 3 x 108 m/s. A wave that is not capable of transmitting its energy through a vacuum is called a mechanical wave (for example, a sound wave or stadium wave).

Electromagnetic Waves Light is an electromagnetic wave, which carries energy in the form of vibrating electric and magnetic fields. Unlike other waves, electromagnetic waves are capable of transmitting its energy through a vacuum (like empty space). All electromagnetic radiation travels through a vacuum at the same speed: c = 3 x 108 m/s. A wave that is not capable of transmitting its energy through a vacuum is called a mechanical wave (for example, a sound wave or stadium wave).

ELECTROMAGNETIC RADIATION SPECTRUM

Increasing Wavelength Increasing Frequency

The Wave Equation and Light The speed of light is related to its frequency and wavelength by the same wave equation: v = f λ. As the frequency of a light wave increases, the wavelength of light decreases. As the frequency of a light wave decreases, the wavelength of light increases.

Example: A microwave has a wavelength of 20. 0 μm Example: A microwave has a wavelength of 20.0 μm. What is the frequency of this wave (assuming it is travelling in a vacuum)? (1 μm = 10-6 m)

Example: A microwave has a wavelength of 20. 0 μm Example: A microwave has a wavelength of 20.0 μm. What is the frequency of this wave (assuming it is travelling in a vacuum)? (1 μm = 10-6 m) Wavelength = 20x10-6 m

Example: A microwave has a wavelength of 20. 0 μm Example: A microwave has a wavelength of 20.0 μm. What is the frequency of this wave (assuming it is travelling in a vacuum)? (1 μm = 10-6 m) Wavelength = 20x10-6 m Speed = 3x108 m/s

Example: A microwave has a wavelength of 20. 0 μm Example: A microwave has a wavelength of 20.0 μm. What is the frequency of this wave (assuming it is travelling in a vacuum)? (1 μm = 10-6 m) Wavelength = 20x10-6 m Speed = 3x108 m/s Frequency = ?

Example: A microwave has a wavelength of 20. 0 μm Example: A microwave has a wavelength of 20.0 μm. What is the frequency of this wave (assuming it is travelling in a vacuum)? (1 μm = 10-6 m) Wavelength = 20x10-6 m Speed = 3x108 m/s Frequency = ?

Example: A microwave has a wavelength of 20. 0 μm Example: A microwave has a wavelength of 20.0 μm. What is the frequency of this wave (assuming it is travelling in a vacuum)? (1 μm = 10-6 m) Wavelength = 20x10-6 m Speed = 3x108 m/s 3x108 m/s = f (20x10-6 m) Frequency = ?

3x108 m/s = f (20x10-6 m) (20x10-6 m) (20x10-6 m) Example: A microwave has a wavelength of 20.0 μm. What is the frequency of this wave (assuming it is travelling in a vacuum)? (1 μm = 10-6 m) Wavelength = 20x10-6 m Speed = 3x108 m/s 3x108 m/s = f (20x10-6 m) Frequency = ? (20x10-6 m) (20x10-6 m)

3x108 m/s = f (20x10-6 m) 3x108 m/s = f (20x10-6 m) (20x10-6 m) Example: A microwave has a wavelength of 20.0 μm. What is the frequency of this wave (assuming it is travelling in a vacuum)? (1 μm = 10-6 m) Wavelength = 20x10-6 m Speed = 3x108 m/s 3x108 m/s = f (20x10-6 m) Frequency = ? (20x10-6 m) (20x10-6 m) 3x108 m/s = f (20x10-6 m)

3x108 m/s = f (20x10-6 m) 3x108 m/s = f f = 1.5 x 1013 Hz (20x10-6 m) Example: A microwave has a wavelength of 20.0 μm. What is the frequency of this wave (assuming it is travelling in a vacuum)? (1 μm = 10-6 m) Wavelength = 20x10-6 m Speed = 3x108 m/s 3x108 m/s = f (20x10-6 m) Frequency = ? (20x10-6 m) (20x10-6 m) 3x108 m/s = f (20x10-6 m) f = 1.5 x 1013 Hz

“Bending” Light

The Bending of Light Observe what happens to how you “see” the object in water—which depends on the light that reaches your eyes.

The Speed of a Wave depends on… The speed of a wave depends only on the medium through which the wave moves. Our discussion of the way waves bend and move through materials will focus on light waves. In a medium such as a vacuum or air, light waves typically move faster. In a medium such as water, glass, or other solid materials, light moves slower.

Bending Analogy: Marching Students

Refraction caused by a change in speed Refraction is the bending of the path of a wave as it passes from one medium (or material) into another medium. Refraction is caused by a change in the speed of the wave upon crossing the boundary between the two materials.

Air Glass What direction will the light ray will be refracted? Remember, a light ray is a wave!

Air Glass

“Normal” to the Boundary (Perpendicular) Air Glass “Normal” to the Boundary (Perpendicular)

Air Glass What if we tried the reverse? Now the light wave is going from glass to air… What happens?

“Normal” to the Boundary (Perpendicular) Air Glass What if we tried the reverse? Now the light wave is going from glass to air… What happens? “Normal” to the Boundary (Perpendicular)

The Direction of Bending The direction of a light ray as it approaches the boundary is called the incident ray. The direction of a light ray after it crosses the boundary is called the refracted ray. A perpendicular line is drawn to the boundary at the point where the incident ray strikes the boundary— this is called the “normal” line, meaning “perpendicular” line. If a light ray goes from a faster medium to a slower medium, it will bend towards the normal. If a light ray goes from a slower medium to a faster medium, it will bend away from the normal. Physics Classroom: Refraction and Reflection http://www.physicsclassroom.com/Physics-Interactives/Refraction-and-Lenses/Refraction

Whiteboard Predictions Draw the situation and predict what will happen to the light ray.

Reflection

Evidence for Wave “Reflection” What is evidence that sound waves reflect?

Evidence for Wave “Reflection” What is evidence that sound waves reflect? Yelling into a cave and hearing an echo… Standing under an acoustical arch and hearing quiet noises clearly…

Evidence for Wave “Reflection” What is evidence that sound waves reflect? Yelling into a cave and hearing an echo… Standing under an acoustical arch and hearing quiet noises clearly… What is evidence that light waves reflect?

Evidence for Wave “Reflection” What is evidence that sound waves reflect? Yelling into a cave and hearing an echo… Standing under an acoustical arch and hearing quiet noises clearly… What is evidence that light waves reflect? Mirrors show a direct reflection, as well as other smooth surfaces like a still pond or a clean spoon… We are able to see matter that doesn’t normally give off light when there is a source of light around…

Law of Reflection For all mirrors, the angle of incidence is equal the angle of reflection. For concave mirrors (bent like the mouth of a cave), images are turned upside down (for example, the front of a spoon). For convex mirrors (bent outward), images are enlarged and distorted (for example, the back of a spoon).

Physics Classroom: Refraction and Reflection http://www Partial Reflection When a wave meets a boundary between two materials, some of the light gets refracted and some gets reflected. Simply put, there is a partial reflection and partial refraction of light waves at a boundary between two materials.

Practice The purpose of the practice is to apply the rules and natural principles discussed in class.

Julius Sumner Miller https://youtu.be/WMnRxFDVw0g