LIGHT AND REFLECTION

Describe how electromagnetic energy is transferred through space as electromagnetic waves of varying

wavelength and frequency

[Visible] Light is the range of frequencies of electromagnetic waves that stimulates the retina of the eyeMajor source is the sun: white light

○ White light which can be separated into red, orange, yellow, green, blue, violet

Received from objects mostly in the form of reflections

Light has particle and wave propertiesFrequency and wavelength are inversely

related.

Classical EM wave theory:

EM waves are transverse waves

In a vacuum…all EM waves travel at the same speed, v = c = 3.00 108 m/s

(186,000 miles/s)Albert A. Michelson became the first American

to win the Nobel prize in science for his series of measurements of the speed of light.

In a vacuum…all EM waves travel in a straight path

This is how our brain locates objects Utilized by the ray model of light

○ Ray represents the path of beam ○ Use of ray diagrams to study travel of light is called

ray or geometric optics

Huygen’s Principle: approximated as rays Lines drawn tangent to the

crest (or trough) of a wave are called wave fronts.

In the ray approximation, lines, called rays, are drawn perpendicular to the wave front.

Wavelets are represented by red curved lines

A luminous body emits light wavesThe rate at which light is emitted from a

source is called the luminous flux, P, and is measured in lumens (lm)

An illuminated body reflects light waves produced by an outside source.The illumination of a of a surface is called

illuminance, E, and is the rate at which light falls on a surfaces. ○ Measured in lux (lx) which is equal to lumens/m2

Some light sources are specified in candela (cd), candle powerA measure of luminous intensity not luminous flux. This is the luminous flux that falls on 1 m2 of a sphere

1m in radius.It is the official SI unit for light intensity

The use of lumens rather than watts is becoming more common in rating a bulb’s light output.Incandescent bulbs generally produce about 15

lumens/wattCFL bulbs produce 50-100 lumens/watt

• Illumination is proportional to 1/r2

ex. If the distance of a surfaces from a point source of light is doubled, the illumination provided is reduced by a factor of four