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Flashcards in Quantum Mechanics Deck (23)
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1

The the very small subatomic level things behave as both what?

Particles (they have momentum) and waves (they diffract, refract, etc.).

2

An electron has a mass (9.11x10^-31 kg) but a beam of electrons does what that’s wave like?

Diffracts through a a gap.

3

Light is a wave propagated by what?

Oscillations in the electric and magnetic fields.

4

If light is a wave what properties are explained?

Diffraction, refraction, etc.

5

What is a particle of light called?

A photon.

6

The de Broglie equation:

λ=h/mv or λ=h/p
Where:
λ is wavelength, m.
h is Planck’s constant, 6.63x10^-34 m^2kgs^-1 (Js).
p is momentum, kgms^-1 (m is mass, kg, v is velocity, ms^-1).

7

What was the traditional idea in the 19th century of black bodies?

They emit all frequencies of light equally and the higher the frequency of radiation the greater the energy.

8

What was the problem with the 19th century idea that a black body gives off radiation evenly and the higher the frequency the more energy it emitted?

When plotted the line tends to infinite energy which violates the conservation of energy principle. If a black body radiator had infinite energy it must be gaining energy from somewhere else.

9

What was actually observed about black body radiators causing the ultraviolet catastrophe?

Energy per unit frequency is still proportional to wavelength across the spectrum, however stars do not emit infinite amounts of light at the short wavelengths.

10

Plank came up with a model of light for fitting the observations of the ultraviolet catastrophe. What does his law state?

That electromagnetic radiation from heated bodies is not emitted as a continuous flow, but is made up of discrete units of energy or quanta.

11

What does the size of quanta depend on?

The fundamental physics constant, Planck’s Constant, 6.63x10^-34Js.

12

Planck's Law equation:

E = hf

Where:
E is energy in J.
h is Planck's Constant, 6.63x10^-34 Js.
f is frequency in Hz.

13

An electron falling down the energy levels releases a what?

A photon.

14

What can be said about the chance of an electron falling down multiple energy levels at once as opposed to single step falls?

An electron falling down multiple steps at once is less likely than single step falls down the energy levels.

15

Electrons can only exist in discrete what around an atom?

Energy levels.

16

What happens if you fire infrared radiation at a negatively charged plate?

No electrons will be liberated no matter how intense the radiation is?

17

What happens if you fire ultraviolet radiation at a negatively charged plate?

Electrons will be liberated with increasing rate if the intensity is increased.

18

One photon can only liberate one what in the photoelectric effect and what is it liberated as?

An electron and it is liberated as a photoelectron.

19

Equation for the photoelectric effect:

hf = Φ + Eu

Where:
hf is the energy of the photon in J.
Φ is the work function of the material in J.
Eu is the energy of the photoelectron once free in J.

20

What is 1eV in J?

1.6x10^-19 J

21

What is 1J in eV?

6.25x10^18 eV.

22

How do we convert between eV and J and vice versa?

If J into eV divide by 1.6x10^-19.
If eV into J multiply by 1.6x10^-19.

23

What is an electron volt?

An electron volt is the energy gained by 1 electron, charge 1.6x10^-19, when it is accelerated across a p.d. of 1V.