Quantum Flashcards
What is the hottest colour?
Violet
What is the order of the electromagnetic spectrum?
Radio, micro, infrared, visible, UV, x-rays, Gamma
What is significant about radio waves?
It has the longest wavelength and the lowest frequency
What is significant about gamma rays?
They have the shortest wavelength and the highest frequency (the most energy)
What is an electron volt?
The energy gain by 1 electron when moved through a potential difference of 1 volt.
Joules ÷ 1.6 x 10 ⁻¹⁹
How do you convert joules into electron volts?
÷ 1.6 x 10 ⁻¹⁹
How do you calculate the energy of an electron?
Work done = Charge x Voltage
Energy = Elementary Charge x Voltage
Energy = 1.6 x 10 ⁻¹⁹ x 1 volt
= 1.6 x 10 ⁻¹⁹
Energy of a typical infrared photon
3 x 10 ⁻¹⁹
What equation do you use to calculate the speed of an electron?
KE = 1/2 mv²
What is quanta?
When looked at really carefully, energy is not smooth but comes out in lumps called quanta
What is a photon?
A packet of energy or quantum of electromagnetic energy
2 equations to calculate the energy of a photon
E = hf
E = hc/λ
h = Planck’s constant
f = frequency
c = speed of light
λ = wavelength
What is Planck’s constant? (h)
6.63 x 10 ⁻ ³⁴ Js
What is the speed of light?
3.00 x 10⁸ ms ⁻ ¹
What is wavelength measured in?
λ or nm
How to calculate power
P = E/t
How does an LED give out light?
An electron loses energy, and gives it to make a photon of light
What is the key concept in quantum?
1 electron gives its electrical energy to make 1 photon
(there is a one to one interaction)
How is conservation of energy linked to photons ?
Energy lost by an electron = Energy of photon
eV = hf
When estimating Planck’s constant using LEDs how would you plot a graph?
eV = hf
(in the form of y=mx+c)
V = h/e f
y axis = voltage
x axis = frequency
Gradient = h/e
Gradient x e = h
What is the photoelectric effect?
The emission of electrons from a metal surface when in the electromagnetic wave above a certain frequency is shone onto a metal surface. The electrons released from the metal are often called photoelectrons.
How to observe the photoelectric effect using a gold leaf electroscope
- Charge a plastic rod by rubbing it with a cloth. (leaving a positive charge)
- Bring the road close to the surface of the metal (zinc) plate on top of the electroscope
- This will attract opposite charges to be brought upwards leaving the gold leaf positively charged and pointing upwards (risen).
- Then place a finger or shine a UV light on the zinc plate to ground it.
Five observations of the gold leaf experiment
- Using visible light on the zinc plate will not release electrons and will have no effect
- Using UV light on the zinc plate will cause electrons to be admitted
- If UV light is above threshold frequency electron emission will be instantaneous
- Increasing the intensity of visible light has no impact
- Increasing the intensity of UV light will increase the number of electrons admitted as long as it’s above threshold frequency
Why can the wave model not explain the photoelectric effect?
Wave theory suggests that electrons are admitted at any frequency if intensity is high enough
However
The photoelectric affect shows that electrons are only admitted when the light is above threshold frequency otherwise light intensity has no impact
Wave theory suggests that electrons gradually gain enough energy to escape the metal
However
The photoelectric effect shows instantaneous admission when the light is above threshold frequency
Wave theory suggests photon energy is spread evenly and shared until built up enough to release an electron
However
The photoelectric effect shows that the energy an electron gains is proportional to a single photon (there is a one-to-one interaction between the photon and electron)
What is threshold frequency?
The minimum frequency needed to release a single electron from a metal surface
What is the work function?
The minimum energy needed to release a single electron from the surface of a metal
Why is there no time delay?
If incident radiation is equal to or above threshold frequency photoelectrons are admitted instantly
(There is a one-to-one interaction between the photon and electron)
What happens to the number of rate of photons if the intensity of radiation is increased?
The number of photons released per second will also increase if above threshold frequency
How do you calculate maximum kinetic energy?
hf = KEmax + φ
KEmax = hf - φ
φ = work function
How is the maximum kinetic energy increased?
Increasing the frequency from blue light photons to UV light increases the kinetic energy of the admitted photoelectrons
(As there’s more energy to spare after the electrons have been freed from the metal)
More kinetic energy after being released = photoelectrons moving faster
What impact does light intensity have on the photoelectric effect?
If the light intensity, the number of photons increases meaning the number of electrons released from the metal will also increase IF ABOVE THRESHOLD FREQUENCY
(going against wave theory which suggests that light of any frequency should be capable of causing photoelectron emission)
What happens to the energy of a photon when it hits a metal surface?
An electron near to the surface of the metal absorbs an individual photon and gains energy equal to the photon energy - which it will then use to release itself from the surface
(energy is conserved)
What did Einstein do in 1905?
He applied the principle of conservation of energy to the interaction between a photon and electron in the photoelectric effect
What happens if the photon that hit the metal surface are not above threshold frequency?
Not a single electron will be removed from the surface of the metal, even if intensity is increased
The electron interacting with the photon remains within the metal and the acquires kinetic energy from the photon that is dispersed as heat to the rest of the metal
How does the energy/frequency a photon has when it strikes a metal surface affect the KE of the photoelectron?
Only a few electrons require the minimum amount of energy to be released. This means that they would have the most left over and maximum kinetic energy.
If the photon strikes the metal surface at threshold frequency, then it will only only have enough energy to release surface electrons with none left to transfer into kinetic energy for the photoelectron
If photon energy is greater than the work function, electrons are instantaneously admitted from the metal surface with the range of kinetic energies - determined by how firmly attach the electrons are to the metal ions
The more energy a photoelectron has leftover after the interaction the more kinetic energy it will contain
How to lay out a graph of KEmax against frequency
It will always give a positive straight line as electrons are being admitted from the metal surface and there is a one-to-one interaction
Y-axis = KEmax
X-axis = Frequency
Gradient = h
Y-intercept = work function
X-intercept = threshold frequency
Describe the graph of frequency against wavelength representing the photoelectric effect
- As f increases then photon energy increases and above the threshold frequency electrons are emitted
- As wavelength increases the energy of the photon decreases.
- Below the work function no electrons will be
emitted. - As we decrease wavelength the energy of the photon increases.
-There is a threshold wavelength above
which no electrons are emitted - Wavelength is inversely proportional to frequency and
E=hf
What did de broglie do?
He proposed that it’s possible for like to act as both a particle and a wave. And all matter has wave and particle properties.
What does the photoelectric effect show?
It shows light acting as a particle
What does the electron refraction experiment show?
Light behaving as a wave
What is matter?
Stuff that has mass
What are De Broglie waves?
(also known as matter waves)
- Matter that has wavelength properties when moving
What is De Broglie wavelength?
The wavelength of particles moving through space
Is momentum a particle or wave of like property?
Particle property
What is the defraction?
How a wave spreads to fit through a gap or around an object
Explain the electron defraction experiment
- They shot a beam of electrons (from an electron gun) through a thin piece of polycrystalline graphite
- The space between the carbon atoms in the graphite were so small, they were similar to the wavelength of electrons.
- This caused the electrons to diffract and overlap forming a defraction/interference pattern at the end of the tube
- Defraction is caused by the interferences of waves therefore it shows light acting as a wave property not a particle property
Why is the electron defraction experiment used to support wave particle duality theory?
Defraction is caused by the interferences of waves, therefore it shows light having wave properties
As well as the photoelectric effect showing light having particle properties
Light has both properties
