6A20.10 Reflection From Curved Surface

Images produced using concave mirror can be made big enough to see in large lecture room.You may want to show that convex mirror does not produce image on wall or screen.

Setup Requirements: Assembled as needed. Use metal plate with arrow or show writing on the end of a light bulb. Shine on wall or movie screen. Adjust separation of mirror and light to obtain clear image.

Equations: 1/o + 1/i = 1/f

Safety Issues: hot bulb, fragile mirror, hot metal plate with arrow

6A40.30 Disappearing Act

Pour some Wesson Oil into a clear container. Put a Pyrex test tube in the oil. Fill the test tube partly with Wesson Oil. The part that is filled with Wesson Oil will seem to disappear. Another version using anisole and an eyedropper is also available.

Setup Requirements:  Minimal. May need towel to clean up oil.

Equations: The index of refraction of the glass is close to that of Wesson oil and anisole. 

Safety Issues:  Keep anisole container taped shut. 

6A40.45 Mirage

A mirage like effect can be demonstrated by shining a laser through a water-sugar mixture. On top is water only. On bottom is water with a large amount of sugar in it. A laser beam pointed slightly upwards will be bent downwards.

Setup Requirements: At least 1 day advance notice needed to prepare solution and fill fishtank. Dark room needed. Place laser near bottom of tank and point slightly upward.

Equations: n(1)sin(a) = n(2) sin(b) The index of refraction of the solution varies so the laser beam is bent in different directions as it move through fluid. 

Safety Issues: Laser, heavy tank filled with water.

6A40.47 Twinkle Twinkle Little Star

Demonstrate " twinkle twinkle little star" by putting slide of constellation in slide projector and adjusting so beam passes just over top of hot hotplate. Adjust so a little out of focus to enlarge star images.

Setup Requirements: Use movie screen or white cardboard. Works best if you have a small class that can come up to the front to see effect. Dark room needed. 

Equations: None

Safety Issues: Red hot hotplate 

6A42.20 Refraction Tank

Move a laser beam around a tank of water containing some non-dairy creamer or amber Pinesol. Demonstrate refraction of beam entering water and total internal reflection of beam leaving water.

Setup Requirements: A tank filled with water is used.  Allow time to fill. Add small amount of non dairy creamer or amber Pinesol. "Canned Fog" available to make beam visible in air.

Equations: Snell's Law  n(1)sin(a) = n(2) sin(b)

Safety Issues: Laser in use, Do not point at students. Heavy tank filled with water. 

6A44.40 Laser and Fiber Optics

Shine a laser into a curved plastic rod. Total internal reflection allows beam to come out at right angles to initial direction.

Setup Requirements: Minimal 

Equations: Total IR occurs when Snell's Law gives sin(A) > 1. 

Safety Issues: Laser 

6A44.45 Frustrated Total Internal Reflection

Shine a laser along the plastic bar. Orient the laser so that total internal reflection occurs and you have the laser beam reflected from side to side. Put oil at one of the places where the laser beam is reflected. Press down on the oil with a finger. The beam will come and go as you press down and remove finger.

Setup Requirements: Assembled as needed. Use one of the brighter lasers. Use mineral oil. Have towel handy to clean up oil and fingers.

Equations: Total internal reflection occurs when incident angle and index of refraction of the materials would give an outgoing value of sin(A) > 1 in Snell's Law. Instead of refraction, internal reflection occurs. Putting oil on the plastic and pressing down changes the index of refraction so total internal reflection does not occur.  

Safety Issues: Do not shine laser at students. Do no look directly at laser. 

6A44.46 Total Internal Reflection in Cylinder

Shine laser beam from the brighter red laser on edge of notch on one end of cylinder. Internal reflection will cause the beam to spiral around the cylinder.

Setup Requirements: Minimal  Dark room needed.

Equations: Total internal reflection occurs when Snell's Law gives sin(A) > 1.

Safety Issues: Extra bright laser. Do not point at students. 

6A60.20 Thick Lens In Water

Instead of filling the air with chalk dust to show laser beam, put a thick lens under water. Add a small amount of non-dairy creamer to make laser beam visible. Why thick lens? What happens if lens is filled with air rather than being solid glass?

Setup Requirements: Time needed to fill fishtank. Use extra bright red laser.

Equations: Since the index of refraction of water is closer to that of glass the light will be bent less than in air. If you use an air lens, a convex lens acts like a concave lens and vice versa.

Safety Issues: Laser. Heavy tank filled with water

6A60.30 Thin Lens Projection

Project the filament of a lamp or writing on end of bulb with a thin lens. Device to produce image of arrow also available.

Setup Requirements: Assembled as needed.

Equations:1/o + 1/i = 1/f

Safety Issues: Hot light bulb. AC line voltage present.