Nature of Light

So today we went over questions 13 through 16 in class today. The answers can be seen in today's slides.
If there's anyone wondering what the orignal questions are, they go as followed:

13)When a screen is illuminated by two closely spaced parallel, single-filament light sources, no interference is observed. What major condition for interference has not been satisfied?

14) If Young's experiment was done completely in glass, how would the interference pattern change from that observed in air, using the same equipment and experimental set-up?

15) A student is measuring the wavelength of light produced by a sodium vapour lamp. The light is directed through two slits with a separation of 0.15 mm. The interference pattern change screen 3.0 m away. The student found that the distance between the first and the eighth consecutive dark lines was 8.00 cm. What was the wavelength emitted by the sodium vapour lamp.

16) An interference pattern is formed on a screen when a helium-neon laser light (λ= 6.328 x 10^-7 m) is directed towards it through two slits. If the slits are 43 μm apart and the screen is 2.5 m away, what will be the separation of adjacent nodal lines?

I realize that having answers without the questions aren't very beneficial.

We also did some reading out loud today as we read about the "Photoelectric Effect and the Wave Particle Duality."
It was Albert Einstein who proposed the idea that light is made of photons.
The Photoelectric effect itself refers to the ejection of electrons from the surface of a metal when it is exposed to electromagnetic radition. *as defined by our pink booklet.
To study this we would use a photocell that has two metal electrodes sealed in an evacuated tube. The air is removed so in doesn't stop the electrons from moving. The large eletrode is a cathode and coated with cesium or another alkali metal. The second electrode is an anode that is made of thin wire so it doesn't block radiation. To allow ultraviolet wavelengths to pass through the tube, it is often made of quartz. A power source is thus connected to the anode and cathode so that the negative side of the source is attached to the cathode and the anode on its positive side. The ammeter can measure the current flowing through the circuit. When radiation does not fall on the cathode, there is no current flow in the circuit. The current is due to electrons called photoelectrons being ejected by the cathode due to radiation and are attracted to the anode. The ammeter in the circuit can thus measure the current flow.

That's the basis of what we learned today. Then we were assigned to finish the last questions from the pink booklet.
Remember: Test on Wednesday! Good luck everyone.
That is all. Good day.