Learning Objective:
Understanding the basic nature of light
Standard:
PH 5
Warm up:
{Predictive, Diagnostic} What is Light? Is light a wave or a particle? If light is a wave, what do you think is oscillating?
Introduction to light
This video is simple overview – you should watch this on your own after class….
Historical backgrounds – myths and measurements.
What is an electromagnetic wave?
Q: if the electric and magnetic fields are in the y and z direction, what is the axis of propagation of the wave?
The Electromagnetic Spectrum:
Key length scales: meters, nanometers, Angstroms
1 nm = 10^-9m, 1 A = 10^-10m
Visible orange light is 6,000A wavelength. What is this wavelength in nanometers? in meters? (use scientific notation).
The Electromagnetic Spectrum – courtesy of Monkey See
The speed of light is known to be 3×10^8 m/s in free space.
Q; Calculate the frequency of visible orange light.
Ans.
Challenge problem:
Alpha Century is actually a binary star with Alpha Century A and B orbiting each other at a distance of 200 AU. Alpha century a is similar to our sun but slightly larger. Assume Alpha century A has the same luminous flux as our sun, calculate its apparent brightness as seen from Earth.
A light year is the distance light travels in one year – it is equal to 9.46 x 1012 km. Alpha Centauri A & B are roughly 4.35 light years away from us. Our sun has a luminous flux of 3.846×10^26 J/s and is 149,600,000 km away. source: Cosmic Distance Scales
Assume Alpha century A has the same luminous flux as our sun, calculate the apparent brightness of as seen from Earth.
Exit Assessment:
How would you use the apparent brightness of a star to measure its distance from Earth?
This is a great video, includes light, astronomy, Mars, remote sensing. Watch it now, I’ll be posting questions later…..
Calculations: Formulas you need to know;
Luminous Flux P {lumens}, Illuminance E {lux} read pg 440-441
Luminous Intensity {candela}
Point Source Illuminance pg 443
GP: Example Problem 1 pg 444
IP: Practice Problems 1,3,4 pg 444