Seeing Things The Laws of Reflection

REVIEW SILT - Image Characteristics Table SizeSame InversionFront to Back LocationEqual to Object Distance, 90º Behind Mirror TypeVirtual

The Laws of Reflection A law in physics describes what happens but does not explain why it happens Exactly how does light reflect off the mirror?

The Laws of Reflection From a Plane Mirror A law in physics describes what happens but does not explain why it happens Exactly how does light reflect off the mirror?

The Laws of Reflection From a Plane Mirror A law in physics describes what happens but does not explain why it happens Exactly how does light reflect off the mirror?

The Laws of Reflection From a Plane Mirror A law in physics describes what happens but does not explain why it happens Exactly how does light reflect off the mirror?

The Laws of Reflection From a Plane Mirror A law in physics describes what happens but does not explain why it happens Exactly how does light reflect off the mirror?

The following Nomenclature is needed to state the laws of reflection.

The “Normal” is an imaginary line that is perpendicular to the Mirror in all directions.

The “Incident Ray” (Incoming Ray) is the ray which meets the Mirror at the “Point of Incidence”.

The “Reflected Ray” is the ray which reflects off the Mirror from the “Point of Incidence”.

The “Angle of Incidence (  i)” is the angle between the Incidence ray and the Normal.

The “Angle of Reflection (  r)” is the angle between the Reflected ray and the Normal.

Time to Observe Reflection Laws Inquiry or Group Lab

The Laws of Reflection From a Plane Mirror Recall the Group Lab

The Laws of Reflection From a Plane Mirror Recall the Group Lab

The Laws of Reflection From a Plane Mirror Recall the Group Lab

The Laws of Reflection From a Plane Mirror 1)The Angle of Incidence (  i) is equal to the Angle of Reflection (  r).In mathematical short form  i =  r Recall the Reflection Laws Inquiry 2) The Incidence ray, the Reflected ray and the Normal are coplanar.

The 2nd Law of Reflection From a Plane Mirror 2)The Incidence ray, the Reflected ray and the Normal are coplanar. This never happens.

The Laws of Reflection also apply to parts of Electromagnetic Spectrum you can not see If you can see the TV in the mirrors you can use the remote to operate the TV. Remotes work with Infra Red radiation.

Periscopes Why U-boat Captains Have To Spin In Circles 8)Use the laws of reflection to show how the Eye/Brain sees the top and bottom of a candle in a periscope?

Periscopes Why U-boat Captains Have To Spin In Circles Roughly parallel rays from the top and bottom of the candle move towards the top mirror

Periscopes Why U-boat Captains Have To Spin In Circles Angle of Incidence = Angle of Reflection (  i =  r ) and the rays move towards the bottom mirror

Periscopes Why U-boat Captains Have To Spin In Circles Angle of Incidence = Angle of Reflection (  i =  r ) and the rays move towards the Eye/Brain mirror Note: This does not predict the Image’s location.

Periscopes Why U-boat Captains Have To Spin In Circles The candle’s image appears erect.

9)Use the laws of reflection to show how the Eye/Brain sees the top and bottom of a candle if the top mirror is be rotated to face backwards? Periscopes Why U-boat Captains Have To Spin In Circles

Periscopes Why U-boat Captains Have To Spin In Circles Roughly parallel rays from the top and bottom of the candle move towards the top mirror

Periscopes Why U-boat Captains Have To Spin In Circles Angle of Incidence = Angle of Reflection (  i =  r ) and the rays move towards the bottom mirror

Periscopes Why U-boat Captains Have To Spin In Circles Angle of Incidence = Angle of Reflection (  i =  r ) and the rays move towards the Eye/Brain mirror Note: This does not predict the Image’s location.

Periscopes Why U-boat Captains Have To Spin In Circles The candle’s image appears inverted.

10)Use the laws of reflection to show how the Eye/Brain sees the top and bottom of a candle if the top mirror is rotated to face sideways? Periscopes Why U-boat Captains Have To Spin In Circles

The candle appears to be sideways. Periscopes Why U-boat Captains Have To Spin In Circles

Periscopes Why U-boat Captains Have To Spin In Circles In other words, Check it out! The man of science has learned to believe in justification, not by faith, but by verification. — Thomas Henry Huxley

Bicycle Reflectors and the Distance to the Moon 4)Use the laws of reflection and geometry to prove light is reflected back, parallel to the incident ray from two mirrors at right angles?

Bicycle Reflectors and the Distance to the Moon At B, let the first Angle of Incidence = Angle of Reflection = x or (  i =  r = x)

Bicycle Reflectors and the Distance to the Moon At C, let the second Angle of Incidence = Angle of Reflection = y or (  i =  r = y)

Bicycle Reflectors and the Distance to the Moon Note  A= 90 º In ∆ABC,  A+x+y = 180 º 90 º +x+y = 180 º  x+y = 90 º The Transversal line BC 2x+2y = 2(x+y) = 2(90 º ) = 180 º  Lines IB and CR are parallel because the interior angles on the same side of the transversal are supplementary

Bicycle Reflectors and the Distance to the Moon This proof is only in two dimensions. In two dimensions, this only proves that the Incident and Reflected ray are in parallel planes. The rays could be drawn on planes perpendicular to (in & out of) the page.

Bicycle Reflectors and the Distance to the Moon If three mirrors are arranged like the corner of a cube,they are called “ corner cube reflector ” or a “ retro reflector ”. They are all connected at right angles to each other, In corner cube reflectors,the Incident ray and final Reflected ray are parallel lines. They are in exactly opposite directions.

Bicycle Reflectors and the Distance to the Moon Corner Cube Reflectors,are used in Bicycle Reflectors because when light is shone on them from something like a car (Incident rays) it is reflected straight back toward the car. The Reflected rays are parallel and in the opposite direction of Incident rays. Laser ranging Corner Cube Reflectors were positioned on the Moon in 1969 by the Apollo 11 astronauts. Laser pulses beamed at the reflectors from Earth, help scientists determine the distance between the earth and Moon to an accuracy of about 3 centimeters.

Bicycle Reflectors and the Distance to the Moon In other words, Check it out! Does the theory work? Arrange three mirrors so they form the corner of a cube. Then shine a laser pointer at them and see if it’s reflected back regardless of the direction you shine the laser. Misting with a spray bottle will make the laser beam visible. Try a Bicycle Reflector It is certainly true that principles cannot be more securely founded than on experience and consciously clear thinking. — Albert Einstein

Signal Mirrors A Signal Mirror is a mirror that reflects from both sides. It also has a hole or transparent spot in its centre Most people have used a normal plane mirror to reflect the sun toward something. When what you are reflecting the sun toward is distant you can’t tell whether you have hit it or not. In order to accurately reflect the sun at a distant object you have to use a Signal Mirror

How to use a Signal Mirror 1)Hold the mirror so that you can see the image (I) of the spot (Sp) the sun makes on your face or body

How to use a Signal Mirror 2)Move the mirror so that you can see what you are aiming at through the hole. It could be a far away boat or plane.

How to use a Signal Mirror 3)Rotate the mirror so that the image of sun spot is seen through (overlaps) the hole in the mirror.

How to use a Signal Mirror 4)When these conditions are met all the light reflecting from the mirror is aimed directly at what you are aiming at. Prove It!

These are the conditions for aiming the mirror correctly. Notice I’ve drawn in the Normal “N” to the centre of the Mirror “C” The Proof of the operation of a Signal Mirror

In triangles CLI and CLSp

The Proof of the operation of a Signal Mirror 1)The Distance IL = SpL from the rules for locating Images.

The Proof of the operation of a Signal Mirror 2)The angle  CLI =  CLSp = 90º from the rules for locating Images.

The Proof of the operation of a Signal Mirror 3)The side CL = CL. (Common Side)

The Proof of the operation of a Signal Mirror 4)Therefore triangle CLI is identical to triangle CLSp (SideAngleSide).

The Proof of the operation of a Signal Mirror 5)Angle  MCS =  LCSp. (VerticallyOppositeAngles)

The Proof of the operation of a Signal Mirror 6)Angle  LCSp =  LCI. (Identical Triangles)

The Proof of the operation of a Signal Mirror 7)Therefore Angles  SCN =  ICN. (Complimentary Angles)

The Proof of the operation of a Signal Mirror 7)Therefore Angles  x =  i =  r. 8)This is the law of reflection. Therefore the light coming from the sun reflects toward what is being aimed at.

The Proof of the operation of a Signal Mirror 7)Since Angles  i =  r, all the light coming from the sun reflects toward what is being aimed at.

Time for a Reality Check