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)