Energy and momentum of a photon (22.1)
Call Kai
Learn
Practice Test
Spaced Repetition
Match
Flashcards
Knowt Play1/9
There's no tags or description
Looks like no tags are added yet.
Name | Mastery | Learn | Test | Matching | Spaced | Call with Kai | Chat |
|---|
No analytics yet
Send a link to your students to track their progress
10 Terms
What is a photon?
A photon is a quantum of energy of electromagnetic radiation.
Photons are massless but have momentum
What is the relationship between energy of a photon, frequency and Plank’s constant?
Eγ = hf
Where Eγ is the energy of a photon (J)
Where h is Plank’s constant (Js) ~ 6.63 × 10-34
Where f is frequency (Hz)
What relationship can be derived from Eγ = hf?
c = fλ
f = c/λ
Therefore:
Eγ = hc/λ
Where Eγ is the energy of a photon (J)
Where h is Plank’s constant (Js) ~ 6.63 × 10-34
Where c is the speed of light (ms-1)
Where λ is wavelength (m)
What is the relationship between the power of light source, the number of photons per unit time and the energy of a photon?
P = N/t x Eγ
Where P is power of light source (W)
Where N/t is number of photons per unit time (s-1)
Where Eγ is the energy of a photon (J)
What are the equations that relate to the momentum of a photon?
pγ = h/λ = Eγ/c
Where pγ is the momentum of a photon (kgms-1)
Where h is Plank’s constant (Js)
Where λ is wavelength (m)
Where Eγ is the energy of a photon (J)
Where c is the speed of light (ms-1)
Equations for momentum that include mass cannot be used
What is the relationship between force and the momentum of a photon?
F = Δpγ / Δt
Where F is force (N)
Where pγ is the momentum of a photon (kgms-1)
Where t is time (s)
When a photon is incident on a black surface or silver surface what are the respective changes in momentum?
Black surface - Δpγ = pγ as the photon is absorbed
Silver surface - Δpγ = 2pγ as the photon is reflected
What is the electron volt?
The electron volt is the amount of energy gained by 1 electron when it’s accelerated across one volt
It is is 1.6 × 10-16 J
This is because V= E/Q - E = VQ
Q of 1 electron = 1.6 × 10-16 C
Therefore, E = 1 x 1.6 × 10-16 = 1.6 × 10-16 J
How do you convert from electron-volts to joules and coulombs?
eV → J - x 1.6 × 10-16
eV → C - /1.6 × 10-16
What is the relationship between electron volts and kinetic energy?
If an electron is accelerated from rest, an electronvolt is equal to the kinetic energy gained:
eV = ½ mv2 = Ek
Where eV is electron volts (J)
Where m is mass of an electron (kg) ~ 9.11 × 10-31
Where v is the velocity of the electron (ms-1)