Physics Class 6: Light, Optics, Quantum Physics

Question 1

speed of light in a vaccuum

Answer 1

c=3 x 10⁸ m/s

Question 2

for electromagnetic waves (EM waves), they can travel through a vacuum and during that travel, speed is constant, so v=c (speed of light). What does this mean for the fundamental equation for waves?

Answer 2

fundamental wave equation is v=λf

so, v = c = λf = 3x10⁸m/s in a vaccuum

Question 3

intensity/energy is proportional to

Answer 3

frequency

and

the square of the wave amplitude. In the case of EM waves, the amplitude is the electric field strength

I∝A²

Question 4

KE_photon = E_photon - E_initial

E_initial is represented by the “work function” of the medium the photon comes into contact with. It is the minimum amount of free energy necessary to release an electron in the form of a photoelectron. If varies from material to material.

Answer 4

on problems, when determining the KE, don’t forget to subtract this amount from energy of the photon

Question 5

in reference to the equation 1/o + 1/i = 1/f, f (focal length) is a positive number for ________lenses/mirrors and negative for ________lenses/mirrors

Answer 5

concave

convex

Question 6

T/F: the image in a flat mirror is always virtual

Answer 6

true

virtual images are upright

Question 7

What does the equation for 1/f look like when an object is “very far from the mirror”

Answer 7

1/o _{(o=object’s distance from mirror)} = 1/∞ = 0

So, 1/i = 1/f, that is, the image is at the focal point

Question 8

if you’re given the energy of a photon in Joules how do you conver it to eV?

Answer 8

divided by e (1.6 x 10^-19 C)

Question 9

work function of a metal surface

Answer 9

its binding energy for its surface electrons (the ones most likely to be ejected)

represented by Φ

When a photon strikes a metal surface, a minimum amount of energy, φ (the work function), is needed to knock an electron off.

Question 10

T/F: photons of light are absorbed or emitted as single instantaneous reactions so the rules for wave theory don’t apply

Answer 10

true

Question 11

equation for KE_{photon (max)}

Answer 11

KE_{photon (max)} = hf - Φ

where Φ is the work function (binding energy of metal for its surface electrons)

Question 12

t/f: the index of refraction is not a property of media but rather describes how a particular light will travel through the media based on its properties

Answer 12

true

therefore, colors will be refracted differently in the same medium. the higher the frequency, the greater the index of refraction (meaning, the more bent)

*This is the process of dispersion

↑index of refraction (n) ↓speed of the light ray through medium

so, ↑frequency light↓speed the light through medium (from n=c/v)

Question 13

what relationship is shown?

Answer 13

graph of inverse relationship