# Ray Diagrams Reflection Images in plane mirrors Ray

• Slides: 26

Ray Diagrams & Reflection Images 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

Normal Incident ray Reflected ray 3

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Reflection • Reflection is light bouncing back from any surface • A mirror is any polished surface that exhibits reflection • Specular reflection is reflection of light off a smooth surface • 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 angle to mirror surface ray that bounced off the surface

The Laws of Reflection incoming ray that hits the surface angle between incident ray and the normal line at right angle to mirror surface angle between reflected ray and the normal ray that bounced off the surface

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 v. Light rays and the laws of reflection help determine how and where an image is formed in a plane mirror. 10

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. 11

Finding the Image light source distance of object from mirror normal mirror apparent distance of object from mirror object-image line apparent light source 1. 2. 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. 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. 13

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. 14

Virtual Images in Plane Mirrors Rays seem to come from behind the mirror, but, of course, they don't. It is virtually as if the rays were coming from behind the mirror. "Virtually": the same as If light energy doesn't flow from the image, the image is "virtual". As far as the eye-brain system is concerned, the effect is the same as would occur if the mirror were absent 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 mirror object reflected incident Image of object 20

Ray Diagram Using 2 Points: Perpendicular ray Reflected ray Incident ray 21

Locating Images in a Plane Mirror Is there any easier way? Of course. . . Draw line & measure Repeat lines behind mirror 2 cm object 3. 5 cm mirror 22

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 object for complicated objects, draw more than two lines 2 cm 3. 2 cm 24

S. A. L. T • 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? 25

PLANE MIRRORS • 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 26