Reflection and Linear Optics

Every point on a luminous or illuminated surface produces light rays in all available directions.

Linear Light Propagation: Observations… Shadows (lunar eclipses); Pinhole camera; Human vision, etc… Solar eclipse: shadows produced by the hands and leaves…

The Reflection of Light Comments: q is the Greek letter “theta” used to label angles The angle of incidence, qi, is equal to the angle of reflection, qr. Incident ray, reflected ray and the normal to the mirror are in the same plane. qi=qr

Light Reflection in Everyday Life Comments: For both specular and diffuse reflection surfaces the law of reflection works perfectly. However, because of the surface structure the results of the reflection are very different! qi = qr Think of shimmering water.

Plane Mirror Non reflective side Object - We use objects like arrows so we can see if the image created ends up upright or upside-down (inverted)

How to Draw a Ray Diagram 1. Draw a straight line from the top of your object to your mirror. (this represents light traveling past your object). Make sure it’s PERPENDICULAR. This is called an INCIDENT RAY Remember, the Head of the arrow goes in the direction the light is moving... this is VERY IMPORTANT!!!!

How to Draw a Ray Diagram 2. draw a line traveling in the opposite direction along the same path THIS IS CALLED THE REFLECTED RAY Remember, the Head of the arrow goes in the direction the light is moving... this is VERY IMPORTANT!!!!

How to Draw a Ray Diagram 3. draw a diagonal line traveling through the tip of the object. THIS IS CALLED THE INCIDENCE RAY

How to Draw a Ray Diagram 4. draw in a “Normal”. This is a line that is drawn perpendicular to the mirror at the point where the line hits the mirror

How to Draw a Ray Diagram 5. Measure the angle between the incidence ray and the normal. this is called the angle of incidence

How to Draw a Ray Diagram 6. Draw a line traveling away from the mirror at the same angle. this is called the angle of reflection

How to Draw a Ray Diagram 7. Now extend the reflected rays behind the mirror. The image is created where they meet. These rays are called virtual rays.

Tada!! How to Draw a Ray Diagram we simply extend the reflected rays backwards to the virtual side of the mirror. ... hmmm... the reflected rays won’t ever meet... Tada!!

Remember: There are 4 characteristics used to describe the image: 1. Size: Same size, larger than, or smaller than the object. 2. Attitude: upright or inverted 3. Location: closer than, farther than, or in the same distance as the object to the mirror 4. Type: Real or Virtual image (can you project it onto a screen?)

Let’s describe our Image using S-A-L-T This image is: 1. SIZE: The same size as our object 2. ATTITUDE: Upright 3. LOCATION: The same distance from the mirror 4. TYPE: Virtual, can’t be projected onto a screen.

Forming Images in a Plane Mirror To form an image it is convenient to use ray diagrams. Pick a point on an object you want to find an image of. Then draw a ray of light emitted by this point and then draw a reflected ray of light. Then choose another ray also emitted by the same point and find the reflected ray corresponding to it. The point where the rays (real image) or their continuation (virtual image) intersect is the point where the image will be created. While drawing a reflected ray always remember that the law of reflection holds for each one of the beams! qi = qr

Forming Images in a Plane Mirror Read only, do not draw. Let’s make sure this makes sense. Forming Images in a Plane Mirror A difference between an object and an image is that one can see an object from anywhere while the image can be seen only from a limited region. This region is called a field of view. qi = qr therefore do = di

Charlie Brown Uses a Mirror Draw a light ray coming from Charlie Brown’s shorts, and reflecting back to his eyes. Draw a light ray coming from Charlie Brown’s shoes, and reflecting back to his eyes. Draw a light ray coming from Charlie Brown’s hat, and reflecting back to his eyes. Draw all of the virtual rays extending back from the reflected rays. Charlie Brown Uses a Mirror

The image in a plane mirror is called a virtual image, meaning that no light rays pass through the image. Rather light rays only appear to originate at the image.