Name ______Date ______

Science 9

Chapter 22

The Nature of Light

Test Study Guide

SECTION 1 WHAT IS LIGHT

Electromagnetic wave (EM wave) – a wave that consists of electric and magnetic fields that vibrate at right angles to each other

·  An electric field surrounds every charged object.

·  A magnetic field surrounds every magnet.

·  They do not need to travel through matter.

Radiation – transfer of energy as electromagnetic waves

Electromagnetic waves are produced by the vibration of electrically charged particles.

The speed of light is 300,000 km/s or 300,000,000 m/s

The major source of energy for the Earth comes from the sun’s EM waves and this is only a small portion of the energy that the sun gives off.

SECTION 2 THE ELECTROMAGNETIC SPECTRUM

Electromagnetic spectrum – all of the frequencies or wavelengths of electromagnetic radiation

Wave / Characteristics / Picture
Radio / ·  Longest wavelength
·  Lowest frequency
·  Changing amplitude or frequency is called modulation
·  AM – amplitude modulation
·  FM – frequency modulation
·  Television used to work with radio waves /

Microwaves / ·  Wave lengths begin to shorten
·  Frequency begins to increase
·  Wavelengths between 1mm and 30cm /
http://www.kradar.com/Pictures/chanpintu/OWL_shouchichezaicesuleida.jpg
Infrared Waves / ·  Wave lengths continue to shorten
·  Frequency continues to lengthen
·  Warmer objects give off infrared rays – The Sun!
·  Wavelengths between 700nm and 1mm /
Visible Light / ·  Waves that have wavelengths between 400nm and 700nm
·  White light is visible light of all the light waves combined
·  The range of colors is called the visible light spectrum
·  The colors of the visible spectrum are Roy G. BIV /
Ultraviolet Light / ·  Wavelengths between 60nm and 400nm
·  Bad effects – can cause skin cancer
·  Good effects – can kill bacteria, helps produce vitamin D / http://sunburntreatmentcenter.com/wp-content/uploads/2010/05/sunburn-3.jpg
X-Rays / ·  Wavelengths between .001nm and 60nm
·  Useful in the medical field and as security devices /
Gamma Rays / ·  Wavelengths shorter than .1nm
·  Used to treat some forms of cancer
·  Used to kill harmful bacteria in food

SECTION 3: INTERACTIONS OF LIGHT WAVES

Reflection – the bouncing back of a ray of light, sound, or heat when the ray hits a surface that it does not go through.

Ex: Mirror

1.  Law of reflection – states that the angle of incidence equals the angel of reflection

Luminous – Objects that produce light, ex: firefly

Illuminated – A visible object that is not a light source ex. moon

Absorption – in optics, the transfer of light energy to particles of matter

Scattering - an interaction of light with matter that causes light to change its energy, direction or motion or both.

Refraction – the bending of a wave as the wave passes between two substances in which the speed of the wave differs

Look at the stem of the flower. You will see refraction.

You can see the colors of the rainbow when white light is refracted through a prism.

http://www.betterphoto.com/uploads/processed/0840/0809280741281img_6957-.jpg

Diffraction – a change in the direction of a wave when the wave finds an obstacle or an edge, such as an opening.

Interference – the combination of two or more waves that result in a single wave.

1.  Constructive interference – results in a wave with greater amplitude than the original waves.

2.  Destructive interference – results in a wave with smaller amplitude than the original waves.

SECTION 4: LIGHT AND COLOR

Transmission – the passing of light or energy through matter

Transparent / Describes matter that allows light to pass through with little interference /
Translucent / Describes matter that transmits light but that does not transmit an image /
Opaque / Describes an object that is not transparent or translucent /

Color of Objects

1.  The colors of light reflected by an opaque object determine the colors you see.

2.  When light strikes a black object, all the colors are absorbed

3.  When you look through the colored transparent or translucent objects, you see the color of light that was transmitted through the material.

Colors of Light

http://lucaskrech.com/blog/wp-content/uploads/2010/01/addsubmixing.jpg

Color Addition – combining colors of light

Primary colors of light – red, blue and green

Color Subtraction – combining colors of pigment

Primary colors of pigment – yellow, cyan and magenta

1