Physics: Light and the Electromagnetic Spectrum

 Consists of all the different wavelengths of electromagnetic radiation, including light, radio waves, and X-rays.

 Low-frequency  Widely used for communication  Produced by longwave radio transmitters, used for some ship and airplane communication and navigation  Long waves have frequencies as low as 30 kHz (30,000 Hz) and wavelengths as long as 10 kilometers  Waves used for AM radio broadcasting is slightly higher on the frequency scale.  This section of the spectrum extends from 540 kHz to 1600 kHz  Higher on the scale are the frequencies used by shortwave radio (2 to 30 megahertz, MHz)  Commonly used for international broadcasting.  Waves in the shortwave band are easily bounced off the ionosphere in the earth’s upper atmosphere, so a shortwave radio broadcast can often be heard halfway around the world.  Still higher frequencies are used for television and FM radio broadcasting.  The FM band uses frequencies from 87.5 MHz to 107.9 MHz  Ordinary television broadcasts use frequencies of between 54 MHz and 216 MHz  The highest frequencies of radio waves are used by UHF (ultra high frequency, covers a range from 300 megahertz to 3.0 gigahertz) television broadcasts and cellular telephones.

 Consists of waves of higher frequency and shorter wavelength.  Range between 1 and 40 gigahertz or GHz (1 GHz = 1 billion Hz).  Has many uses:  Microwave oven- uses intense beams of microwaves to cook food.  The food absorbs the energy of the microwave radiation and quickly becomes very hot as the energy is transformed into heat within the food.  Also widely used in communication, especially between communications satellites and ground stations.  _________ uses reflected radio waves or microwaves to measure the distance and direction of faraway objects.  _________ system emits a brief pulse of microwaves and listens for “echoes.”  By measuring the time between the initial pulse and the echoes, it determines an object’s distance from the transmitter.  Other Uses of RADAR  During WW II: detect enemy planes and ships at a distance  Civilian uses:  monitor airplane traffic at airports  Track hurricanes  Check the speed of vehicles Doppler radar) - highway patrol  Find the speed of an object by sending out radio waves and measuring the time it takes them to return.

 Above the microwaves on the frequency scale and below red visible light in terms of frequency.
 Best known as “heat waves they transmit radiant heat very effectively.
 Our skin can easily detect them as “warmth”
 Also produced by heat lamps.

LEGEND: Red – Topic Blue– Terms Green – Important Orange – Date Purple –Categories/Types Blue Green–Person

 Infrared video cameras allow firefighters, helicopter pilots, soldiers, and other users to see in the dark, even through thick smoke and fog.

 Above the infrared.  Narrow band of frequencies that is perceived by our eyes as visible light.  The only region in the entire electromagnetic spectrum that our eyes are sensitive to is the visible region. How are wavelengths detected by the human eye?  Visible light is a small part of the electromagnetic spectrum that the human eye is capable seeing.  Objects can be seen if they are a source of light.  Most objects around do not give off light on their own.  They can be seen only if light waves from another source reflect off them and into our eyes.  Light waves move in all directions from a light source  When white light is refracted, it can be separated into its component colors.  As light passes through a prism, refraction causes light to bend and separate into many colors.  The colors of visible light are created by electromagnetic energy of various wavelengths (frequencies).

 Frequency is slightly higher than that of the visible light.
 Can kill living cells
 Used to sterile medical instruments (ex. Surgeon scalpel)
 Can cause sunburn but have beneficial effects on our body.
 _________ an important chemicals in our bodies
 produced when UV radiation breaks down compounds called sterols in our skin.

 Higher frequency than ultraviolet.
 Extremely useful because of their ability to easily penetrate many materials.
 Doctors can see through flesh to examine a broken bone.

Used in
 Dentistry
 In airport security
 In industry

 Prolonged exposure is harmful.

 Extremely high frequency.
 Harmful to living tissues
 Excessive exposures can cause painful radiation burns, cancer, or death.
 Useful to mankind:
 In a medical technique called _________.
 Focused beams of _________ are used to destroy cancerous
tumors in a person’s body without harming healthy tissue.
 Also used in irradiators to sterilize adhesive bandages and other medical supplies.

How Light is Transmitted
 __________ is when light bounces off of a Surface
_________ is when light reflects off of a shiny surface like mirror.
 ______________ however, is when light illuminates a dull object.
 _____________ is when light waves move all the way through a material without absorbed.

Opaque, Transparent, and Translucent
 Light passes through some objects but is blocked by others.

___________ materials completely block light from passing through.

_________ materials allow light to pass through with little or no disturbance, objects may or may not color the light, but you can see objects clearly through them.

__________ materials allow only part of the light to pass through, while bouncing the rays off in many directions giving only a blurry view.

1. The incident ray, the reflected ray and the normal all lie in the same plane
2. The angle of incidence = ___________

1. The incident ray, refracted ray and the normal to the refracting surface at the point of incidence, belong to the same plane.

2. _________ : The ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the index of refraction of the second medium to the index of refraction of the first medium. (refer to page 209 of your book)

 “The branch of optics that focuses on the creation of images is called __________

Rules of Geometric Optics
 ______ is a flow of photons with wavelengths. We’ll call these as “light rays.”
 A _________ is a tiny little particle of light, far too small to see individually.
 Light rays travel in __________ in free space.
 Light rays do not________ with each other as they cross.
 Light rays obey the laws of _________
 Light rays travel from the light sources to the ____

_________ is a mirror with a planar reflective surface.  For light rays striking a plane mirror, the angle of reflection equals the _______ Image formation by plane mirror:  If you stand in front of a plane mirror you see your image behind the mirror. The location of the image can be diagramed knowing that the surface of the mirror reflects light with an angle of reflection equal to the incident angle.  Properties of Image:  It is formed  behind the mirror  it is right side up  having same size as that of object  Far behind the surface as the object is in front of it.  We refer to the image as _________

 A reflecting surface having the form of a portion of a sphere
 Ray Diagrams Points:
 One surface of the curved mirror is silvered.

The centre of the sphere is called the centre of curvature C.

 The geometrical centre of the mirror is called its _________
 The line joining the pole of the mirror and its centre of curvature is
called the _________.
 When a parallel beam of light is incident on a spherical mirror, the
point where the reflected ray converge on the principal axis is called
the ______________.

____________
 Sunglasses
 Vehicle
 Security
 Magnifying Glass
______________
 Vehicle
 Light Concentration
 Image Distance

o All virtual images have __________ distances
o All real images have ____________ image distances

 “If the reflecting surface lies on the INSIDE of the curve, is a __________ “.  Rules:

o Rays parallel to the principle axis are reflected towards the _____________.

o A ray passing through the centre of curvature retraces its path

o A ray passing through the principal focus, after reflection is rendered parallel to the ________.

o A ray of light which strikes the mirror at its pole gets ________ according to the law of reflection.

 Image formation in Concave Mirror:

o CASE 1: When the object is placed at the __________, the image is of same size, real and inverted and is at the _______.

o CASE 2: When the object is placed after the ___________, it is seen that the image is real, inverted, small in shape and lies between the ________ C and focus F.

o CASE 3: When the object is placed within the ________ it is seen that image is virtual, erect and enlarged in shape and lies behind the mirror.

o CASE 4: When the object is _________ the centre of curvature and focus,it is seen that image is real, inverted and enlarged and lies outside the centre of curvature.

 “If the reflecting surface lies on the outside of the curve, is a ___________”.

 Rules:

o A ray of light traveling parallel the principal axis after reflection from a convex mirror appears to come from its ____ behind the mirror

o A ray of light traveling towards the ________ of curvature behind the mirror and is reflected back its own path.

 Image formation in convex Mirror:

o The object is placed anywhere in _____ of the convex mirror.

o The ray parallel to the principal axis after reflection appears to come from the _________ behind the mirror.

o Another ray going towards the centre of curvature C behind the mirror gets ________ by the same path.

o The two reflected rays appear to ______ at a point between F and P behind the mirror.

o The image appears to be formed _______ the mirror.

o So the image formed by the convex mirror is virtual, erect and smaller in size with respect to object.