In an experiment to study the photoelectric effect, a scientist measures the kinetic energy of ejected electrons as a function of the frequency of radiation hitting a metal surface. She obtains the following plot. The point labeled " " corresponds to light with a wavelength of . (a) What is the value of in What is the value of the work function of the metal in units of of ejected electrons? (c) What happens when the metal is irradiated with light of frequency less than (d) Note that when the frequency of the light is greater than , the plot shows a straight line with a nonzero slope. Why is this the case? (e) Can you determine the slope of the line segment discussed in part (d)? Explain.
Note taker: Sera ASTR 1345 Light and Energy Observational Astronomers Use telescopes to study actual events and phenomena Ex. Edwin Hubble, Galileo Galilei Theoretical Astronomers Use mathematics and physics-based predictions and theories Ex. Stephen Hawking, Kip Thorne Computational Astronomers Recreate and test complex physical situations with computers Ex. Roadrunner Computer (1,700,000,000,000,000 calculations per second) Where Light Comes From Emitted: an object gives off energy o Depends strongly on temperature Reflected o Emitted light from one object bounces off of another Scattered o Chemicals reflect light unevenly White Light Newton’s Prism o White light (like sunlight) is a combination of all visible colors o A medium of different density will cause light to reflect (bend) Refraction When light is passed through a medium, the path of it gets deviated Light only travels in a straight line at the speed of light “The Light Bucket” - The Telescope A simple refracting telescope o Uses lenses to refract light o Most important astronomical invention Human vision is unreliable o Light enters the small pupil and is focused light detecting cells