Chapter 7 - Quantum behavior

Question 1

Intensity =

Answer 1

Power/ Area

Question 2

what does the gigacounter experiment tell us?

Answer 2

As the radiation arrives randomly we know that gamma rays are lumpy in nature. we call the lumps/packets quanta or phtons for em radiation.

Question 3

What is the photoelectrc effect?

Answer 3

Light/em radiation can cause e- to be ejected from a metal provided the frequency of that radiation is high enough.

Question 4

E=

Answer 4

hf (h=6.6x10^-34Js)

Question 5

rough wavelength of a visible photon?

Answer 5

500nm = 5x10^-7m

Question 6

What is the work function (ϕ)?

Answer 6

The minimum energy required for a e- to escape a metal. Its minimum energy because its for the furthest away e- from the nucleus.

Question 7

(work function one) hf=

Answer 7

ϕ + Ke max

Question 8

how are energy and potential difference linked (LED)?

Answer 8

E=vQ => v=p.e/Q

Question 9

how much energy does a electron gain when passed through 5000V?

Answer 9

5000eV when e is the charge on an e-

Question 10

What is an electron volt?

Answer 10

1eV is the work done on an e- when it is passed through a p.d of 1V

Question 11

What is quantum amplitude?

Answer 11

the vector sum of all the phasor from all possible paths at a point.

Question 12

What is quantum probability?

Answer 12

Q.P ∝ (Q.A)^2 , its the probability of a photon arrives at a point.

Question 13

Which paths are important when we look at all paths and why?

Answer 13

The shorter paths , as their trip times are more similar and their phasors will align giving a high quantum amplitude. (high prob it arrives at the detector)

Question 14

Why do the more unusual paths become less significant?

Answer 14

There is another equally unusually path which will arrive in antiphase which cause these paths phasors to curl up and contribute little.

Question 15

What does the resultant phasors when considering all paths look like.

Answer 15

Question 16

Wht happens if we block some of the more unusual paths?

Answer 16

The phasors will curl up less as there are less pairs of phasors in antiphase arrive from these paths, this gives a highes resultant .

This is essentially a diffraction grating.

Question 17

Why are the edegs of a mirror curved in order to create a focus? (same for a lens?)

Answer 17

Curving the edges of the mirror means that the paths differance at this point is more similar and so is path time which means these phasors are all going to arrive inphase at the focus which creats a very high Q.P.

In a lens The shorter central path passes through more dense matherial which slows it down more the the other paths this means the trip tims are once again mad eto be the same.

Question 18

What makes electrons different to photons?

Answer 18

They have a mass and can be acccelerated using a p.d

have a charge

Question 19

What is de Broylie equation for particles with mass showing quantum behavior.

λ=

Answer 19

h/mv for v<<c>
</c>

Question 20

how can you diffract electrons?

Answer 20

You need a very small slit due to the tiny de broylie wavelength of a e-

You use a graphite lattice as a diffraction grating.

As there are many layers you get rings insted of fringes which are observed on a phospur screen (turns green)

λ ∝ 1/√v so as voltage increases wavelength degcreases and ring spacing decreases.