EM RADIATION Flashcards
(25 cards)
What occurs when light with high enough frequency shines on metals?
Photoelectrons are released.
What happens if the incident frequency is less than the threshold frequency (ƒT)?
No photoelectrons are emitted.
What is the relationship between the rate of electron emission and intensity?
Rate of electron emission is proportional to intensity.
Why could the photoelectric effect not be explained by wave theory?
Wave theory states that energy is proportional to intensity, and energy would spread evenly across the wavefront.
What is the equation relating energy levels?
E = hƒ = hc/λ
What condition must be met for electron release?
hƒ must be greater than or equal to φ (work function).
What is the equation for maximum kinetic energy (Ek max) of an electron?
hƒ = φ + Ek max
What does stopping potential give?
Maximum kinetic energy (Ek max).
How can an electron move down an energy level?
By photoemission.
What does e × V represent?
Kinetic energy carried by an electron accelerated through a 1V potential difference.
What is the energy gained by an electron equal to?
The accelerating potential difference.
How is the energy carried by each photon calculated?
It is equal to the difference in energy between the two levels: ∆E = E2 − E1 = hƒ.
What happens during excitation of electrons?
Electrons move up energy levels if they absorb a photon with sufficient energy.
What occurs during de-excitation?
Electrons emit photons and move down energy levels.
What does the energy of the emitted photon equal during de-excitation?
hƒ = E1 − E2 (where E2 is the lower level).
What happens when an electron is removed from an atom?
It is ionised.
What is the ground state in terms of energy?
It is referred to as ‘ionisation energy’.
What do line spectra indicate?
Transitions between discrete energy levels in atoms.
What is observed when looking at a tube of glowing gas through a prism?
A spectrum of discrete lines, unique to each element.
What is the process in a fluorescent tube?
High voltage ionises mercury, exciting electrons, which emit UV photons that excite phosphor coating, leading to visible light emission.
What does wave-particle duality refer to?
Interference and diffraction show light as a wave, while the photoelectric effect shows it as a particle.
What does electron diffraction demonstrate?
The wave nature of electrons.
What is the de Broglie wavelength equation?
λ = h/mv.
What is a vacuum photocell?
A glass tube containing a photocathode and photoanode that emits electrons when light of frequency ≥ ƒT is incident on the photocathode.
