# LightTravel

OP34 show that light travels in straight lines and explain how shadows are formed

To know that when light from a source is blocked a shadow is formed.

Apparatus

A strong torch, comb

Method

Shine the torch through the comb.

Results Observations

What can you see?

How can you explain it?

Why does every tooth cast a shadow?

Where is the light being blocked.

Title OB34 Show that light travels in straight lines

Apparatus

Power Pack, Ray Box, Piece of Card with hole in it

Method

Diagram

Safety Concerns

Do Not Look at the light bulb when on.

Do Not hold it when on.

Results / Observations

What did you see or notice

Conclusions

Light travels in straight lines

Eclipse

Follow the link to see how a Solar eclipse travels across the planet

http://www.turkeytravelplanner.com/special/eclipse/

and one for the future 2017 across the US of America

Shadows and the effect of the location of the source

Speed of Light

Light moves! It moves very quickly, in fact it moves

Speed of light in a vacuum = 2.997925 ± 0.000002 x 108 m/s.

The first measurement of the speed of light was made by the Danish astronomer, Ole Rømer (1644–1710) about the year 1676. He observed the planet Jupiter and its satellites. Each of these satellites is eclipsed when it moves behind the planet. The time between successive eclipses of a particular satellite should be the same. Rømer found that when the earth was approaching Jupiter the eclipses became progressively earlier and that when the earth was receding from Jupiter the eclipses became progressively later.

Finding the Speed of Light with

Marshmallows-A Take-Home Lab

Robert H. Stauffer, Jr., Cimarron-Memorial High School, Las Vegas, Nevada, USA

I have heard that at 16 years old, Albert Einstein constantly wondered what it would be like to ride on a beam of light. Students in physics always seem to be fascinated by the properties of light. However, speed-of-light demonstrations often require extensive preparation or expensive equipment. I have prepared a simple classroom demonstration that the students can also use as a take-home lab.

The activity requires a microwave oven, a microwave-safe casserole dish, a bag of marshmallows, and a ruler. (The oven must be of the type that has no mechanical motion-no turntable or rotating mirror. If there is a turn-table, remove it first.) First, open the marshmallows and place them in the casserole dish, completely covering it with a layer one marshmallow thick. Next, put the dish of marshmallows in the microwave and cook on low heat. Microwaves do not cook evenly and the marshmallows will begin to melt at the hottest spots in the microwave. (I leaned this from our Food Science teacher Anita Cornwall.) Heat the marshmallows until they begin to melt in four or five different spots. Remove the dish from the microwave and observe the melted spots. Take the ruler and measure the distance between the melted spots. You will find that one distance repeats over and over. This distance will correspond to half the wavelength of the microwave, about 6 cm. Now turn the oven around and look for a small sign that gives you the frequency of the microwave. Most commercial microwaves operate at 2450 MHz.

All you do now is multiply the frequency by the wavelength. The product is the speed of light.

Example:

Velocity = Frequency ´ Wavelength

Velocity = 2450 MHz ´ 0.122 m

Velocity = 2.99 ´ 108 m/s

This works in my physics class, often with less than 5% error. Then the students can eat the marshmallows.