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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