Ray Diagrams & ReflectionImages in plane mirrors
Ray Diagrams• Light travels in a straight line• A light ray is represented by a
straight line and an arrow showing the direction and ‘straight-line’ path of light
Incident ray
Normal
Reflected ray
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Reflection• Reflection is light
bouncing back from any surface
• Specular reflection is reflection of light off a smooth surface
• A mirror is any polished surface that exhibits reflection
• Diffuse reflection is reflection of light off a surface that is not smooth
Specular Reflection
Diffuse Reflection
The Laws of Reflection
incoming ray that hits the surface
line at right angleto mirror surface
ray that bouncedoff the surface
The Laws of Reflection
incoming ray that hits the surface
line at right angleto mirror surface
ray that bouncedoff the surface
angle between incident ray and the normal
angle between reflected ray and the normal
Laws of Reflection
1. The angle of incidence equals the angle of reflection i = r
2. The incident ray,the reflected ray,and the normal all lie in the same plane
Using Light Rays to Locate an Image
Light rays and the laws of reflection help determine how and where an image is formed in a plane mirror.
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We all know that light travels in a straight line.
When your eyes detect reflected light from plane mirrors, your brain projects the light rays back in a straight line.
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Finding the Image
mirror
normal
light source
apparent light source
distance of objectfrom mirror
apparentdistance of objectfrom mirror
object-image line
1. Distance from object to mirror = distance from image to mirror. The image appears to be the same distance behind the mirror as the object is in front of the mirror.
2. Object-image line is perpendicular to the mirror.
Types of Images
Real Images- mirrors can produce images that can be projected on a screen. A real image is ALWAYS inverted and appears in front of the mirror.
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Virtual Image- mirrors can also produce images that cannot be projected on a screen. A virtual image is ALWAYS upright and appears behind the mirror.
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Virtual Images in Plane Mirrors
"Virtually": the same asIf light energy doesn't flow from the image, the image is "virtual".
Rays seem to come from behindthe mirror, but, of course, theydon't. It is virtually as if the rayswere coming from behind the mirror.
As far as the eye-brain system isconcerned, the effect is the sameas would occur if the mirror wereabsent and the chess piece were actually located at the spot labeled "virtual image".
Reflection of Light Source
Reflection of an Object
Finding the Image with Rays
In a plane mirror the image is:• virtual (the light rays do not
really converge, our brains just think they do.
• the same size as the object.• the same distance behind
the mirror as the object is in front.
• laterally inverted (right becomes left)
• upright
Locating images in a Plane Mirror
object
mirror
Image of object
reflected
incident
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Perpendicular ray
Incident ray
Reflectedray
Ray Diagram Using 2 Points:
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Locating Images in a Plane Mirror
Is there any easier way? Of course...
mirror
2cm 2cm
3.5cm 3.5cm
object
Draw line & measure Repeat lines behind mirror
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Image Formation in Plane Mirrors
Locating Images in a Plane Mirror
•From top of object, draw a line perpendicular to mirror (along normal)•measure the distance of this line and extend the line, the same distance, behind the mirror•repeat this step from the bottom of the objectfor complicated objects, draw more than two lines
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2 cm
2 cm
3.2 cm
• SALT is used to describe images formed by mirrors.
1. S- Size: compared to original object is it same size, smaller or bigger?
2. A- Attitude: which way the image is oriented compared to the original object (upright or inverted).
3. L- Location: location of the image (in front or behind the mirror).
4. T- Type: is the image a real image or virtual image?
S.A.L.T
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• Characteristics of a plane mirror image:
1. Object size= Image Size
2. Object distance from mirror= image distance from mirror
3. Attitude (orientation) is ALWAYS upright
4. ALWAYS forms a virtual image
5. Image is reversed- left to right
PLANE MIRRORS
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