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# Light

Chapter 2 - Waves, E.M. Spectrum, Refraction
by

## Mr. Duke

on 4 September 2012

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#### Transcript of Light

An electromagnetic wave is a wave that transfers electrical and magnetic energy. Reflected

Transmitted

Absorbed Transparent Translucent The electromagnetic spectrum is the complete range of electromagnetic waves placed in order of increasing wavelength. Electromagnetic waves that we can see are called visible light. Light Waves What would happen if... A wave is an oscillation that transfers energy from place to place. What are waves?! Energy is the ability to do work
(i.e., to make things happen) What do waves travel through? Gases (e.g., air)
Liquid (e.g., water, milk)
Solids (e.g., a length of rope) These are called mediums.
A medium is a material that waves can travel through. Question: Do all waves require a medium
to travel through? NOPE! Some waves do not require a medium to travel through.
Light can travel and carry energy through EMPTY space.
Waves that can travel without a medium are called electromagnetic waves. When energy causes something
to vibrate, a wave is produced. Properties of Waves: The crest is the highest point of the wave. The trough is the lowest point of the wave. When a wave travels through a medium, it does not carry the medium with it. The amplitude is the distance
between a crest or trough and
the rest position. The wavelength is the distance between two troughs or two crests of a wave. Rest Position Rest Position The frequency of a wave is the number of complete waves that pass a given point in a certain amount of time. Frequency is measured in units called hertz (Hz). 1 wave/sec = 1 Hz Electromagnetic Waves An electromagnetic wave consists of vibrating electric and magnetic fields that move through space at the speed of light. Remember, electromagetic waves do not travel through a medium! The energy that is transfered through space by electromagnetic waves is called electromagnetic radiation. All electromagnetic waves travel at the same speed in a vacuum, about 300,000 km/sec. This speed is called the speed of light. It is the speed limit of the universe. Electromagnetic Spectrum All electromagnetic waves travel at the speed of light, or 300,000 kilometers per second (that's 670,616,629 mph!). Visible Light When light strikes an object, the light can be: Most objects can be classified as: A translucent object scatters light as it passes through. An opaque object reflects OR absorbs the light that strikes it. Refraction If the medium changes, the speed of the light waves also change. This causes the light to bend. Light travels in straight lines if the medium it travels through does not change. Refraction is the bending of waves due to a change in speed. Vocabulary:
Medium: the material through which a wave travels.

Question: What kind of medium do sound waves travel through? The light has to enter at an ANGLE! Suppose ripples move from one side of a lake to the other. Does the water move across the lake? What is an electromagnetic wave?
Mechanical waves are waves that travel through a medium.
For example, sound waves are mechanical waves because they travel through the air.

Electromagnetic waves are waves that DO NOT travel through a medium.
For example, light waves coming from the sun are electromagnetic waves because they can travel through empty space. A transparent object allows light to be transmitted through it without being scattered. Opaque Light is transmitted when it passes THROUGH an object. Light is Reflected when it BOUNCES OFF of an object. Light is abosrbed when it goes IN to object. The color of an opaque object is determined by the wavelength of light that is relfected. The color of an translucent object is determined by the wavelength of light that is transmitted through it. Pair-share:
What is happening in this picture and why? Radio Microwave Infrared Visible Ultraviolet X-Ray Gamma Ray Examples: light, radio waves
Not examples: sound waves, ocean waves
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