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 eye Major 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 properties Frequency 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  10 8 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 waves The 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/m 2

 Some light sources are specified in candela (cd), candle power A measure of luminous intensity not luminous flux. This is the luminous flux that falls on 1 m 2 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/watt CFL bulbs produce lumens/watt

Illumination is proportional to 1/r 2 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