Light and the Electromagnetic Spectrum

Question 1

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

Answer 1

Electromagnetic Spectrum

Question 2

 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.

Answer 2

Radio Waves

Question 3

 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.

Answer 3

Microwaves
Radio Detection And Ranging
rada

Question 4

 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.

Answer 4

INFRARED

Question 5

 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).

Answer 5

Visible Light/ White Light

Question 6

___________
 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.

Answer 6

Ultraviolet
Vitamin D

Question 7

 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.

Answer 7

X-Rays

Question 8

 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.

Answer 8

Gamma Rays
radiotherapy.
gamma radiation

Question 9

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.

Answer 9

Reflection
Specular reflection
Diffuse reflection
Transmission of light

Question 10

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.

Answer 10

 Opaque

 Transparent

 Translucent

Question 11

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

Answer 11

Law of Reflection
Angle of reflection

Question 12

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)

Answer 12

Law of Refraction
Snell’s Law

Question 13

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

Answer 13

Geometric optics”

Question 14

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 ____

Answer 14

Light
photon
straight lines
interfere
reflection and refraction.
Eye.

Question 15

_________ 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 _________

Answer 15

A plane mirror
angle of incidence.
virtual image.

Question 16

_____________
 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 ______________.

Answer 16

Spherical mirror

pole (P)
principal axis.
principal focus F.

Question 17

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

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

Answer 17

CONVEX MIRROR:
CONCAVE MIRROR:

negative
positive

Question 18

 “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.

Answer 18

concave mirror”.
principle focus of the mirror.
principal axis.
reflected
center of curvature
center
centre of curvature
centre
focus of the mirror
between

Question 19

 “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.

Answer 19

Convex mirror
focus
centre
front
focus F
reflected
intersect
behind