Light Interactions

What is light? Light is an electromagnetic (EM) wave. An EM wave is a wave that consists of changing electric and magnetic fields. EM waves require no matter through which to travel. EM waves can be produced by the vibration of charged particles. The speed of light in a vacuum is about 300,000,000 m/s. EM waves from the sun are the major source of energy for Earth.

The Electromagnetic Spectrum All electromagnetic (EM) waves travel at the speed of light. EM waves differ only by wavelength and frequency. The entire range of EM waves is called the electromagnetic spectrum.

Radio waves are used for communication. AM means amplitude modulation FM means frequency modulation PhET Simulation

Microwaves are used in cooking and in radar. PhET Simulation

The absorption of infrared waves is felt as an increase in temperature.

Visible Light Visible light is the narrow range of wavelengths that humans can see. Different wavelengths are seen as different colors.

Ultraviolet Light Killing bacteria Producing vitamin C Can cause sunburns

Bees see UV light… So they see the world differently than we do!

X-Rays

Gamma Rays

Light Interactions The law of reflection states that the angle of incidence is equal to the angle of reflection. Things that are luminous can be seen because they produce their own light. Things that are illuminated can be seen because light reflects off them. Absorption is the transfer of light energy to particles of matter. Scattering is an interaction of light with matter that causes light to change direction.

Light Interactions Refraction of light waves can create optical illusions and can separate white light into separate colors. Diffraction depends on the light’s wavelength. Light waves diffract more when traveling through a narrow opening. Interference can be constructive or destructive. Interference of light waves can cause bright and dark bands.

Law of Reflection: angle of incidence = the angle of reflection

Convex Mirrors Curved outward Spreads out light Virtual images Allows wider images “Objects in mirror are closer than they appear”

Concave Mirrors “Cave in” Converge light Create real or virtual images

Absorption & Scattering

Polarizing Lenses

Refraction

Refraction

Convex Lens Thicker in the middle, thinner on the edges Converging rays Can make a real (upside down and can be projected) image Can make a virtual image (right side up) Can magnify

Concave Lens Thinner in the middle, thicker on the edges Concave “caves” in Diverging rays Makes only virtual images Makes something look smaller

Diffraction & Interference

Do You See What I See?

March 27, 2015 Do Now: Angles of Reflection (share protractors) Take out HW No homework tonight 

Light & Color Objects are transparent, translucent, or opaque depending on their ability to transmit light. Colors of opaque objects are determined by the color of light that they reflect. Colors of translucent and transparent objects are determined by the color of light they transmit. White light is a mixture of all colors of light. Light combines by color addition. The primary colors of light are red, blue, and green. Pigments give objects color. Pigments combine by color subtraction. The primary pigments are magenta, cyan, and yellow.

Objects are transparent, translucent, or opaque depending on their ability to transmit light.

Colors of opaque objects are determined by the color of light that they reflect.

Colors of translucent and transparent objects are determined by the color of light they transmit.

Light combines by color addition Light combines by color addition. The primary colors of light are red, blue, and green.

Pigments combine by color subtraction.

The primary pigments are magenta, cyan, and yellow.

Question 1 Ultraviolet light has a higher frequency than infrared light has. Which statement about visible light is true? Blue light has a longer wavelength than orange light has. Green light has a higher frequency than violet light has. Yellow light has a shorter wavelength than blue light has. Red light has a lower frequency than green light has.

Question 1 Ultraviolet light has a higher frequency than infrared light has. Which statement about visible light is true? Blue light has a longer wavelength than orange light has. Green light has a higher frequency than violet light has. Yellow light has a shorter wavelength than blue light has. Red light has a lower frequency than green light has.

Question 2 Which light interaction explains why you can see things that do not produce their own light? absorption reflection refraction diffraction

Question 2 Which light interaction explains why you can see things that do not produce their own light? absorption reflection refraction diffraction

Question 3 Which electromagnetic waves is the eye able to see? Red, green, and ultraviolet Red, infrared, and yellow Blue, green, and ultraviolet Orange, green, and red

Question 3 Which electromagnetic waves is the eye able to see? Red, green, and ultraviolet Red, infrared, and yellow Blue, green, and ultraviolet Orange, green, and red