5.5 Photoelectric effect and Atomic Spectra Flashcards
What’s the photoelectric effect?
The photoelectric effect is the phenomena that electrons are emitted from a metal surface from absorption of EM radiation
Electrons removes are called photoelectrons
This proves that light is quantised
- carried in discrete packets
What’s the work function, Φ
Φ is the minimum energy required to remove electrons from a surface
E=Φ+Ek
Where Ek = kinetic energy, 1/2 x mv^2
hf=Φ + 1/2 x mv^2
So this shows that there is energy used to remove the electron, then the rest is used for its movement
What is f, in hf=Φ +1/2 x mv^2?
As Φ is the minimum energy required, f is the threshold frequency (minimum frequency required)
E(Φ)=h x threshold frequency
How does intensity of the light effect the photoelectric effect?
In order for photoelectrons to be emitted, Φ must be met
if not, then the intensity doesn’t matter
But if Φ is met, then there are more electrons emitted with a higher intensity
What’s the gold leaf electroscope experiment?
A zinc plate is attached to a gold leaf
- the gold leaf initially is negatively charged, same as the zinc plate
- then uv light is used to emit photoelectrons
- this then causes the repel of the leaf to stop, as the electrons are gone, so the leaf drops back down
How do electrons sit in atoms?
Electrons will all have a set energy level
The higher the energy level, the higher it is, n
They can gain energy from photons, and move up and back down
Cant go below their set level
What’s the atomic spectra?
When electrons absorb or emit photons, they release different EM waves
We can tell which atom is what through what they emit
Each frequency is seen as a separate/ discrete line of a different colour
Why do dark absorption lines appear in a star’s spectrum?
A star emits a continuous spectrum of light.
Elements’ electrons in the star’s atmosphere absorb specific wavelengths of light.
- the wavelengths absorbed depend on the energy level difference as E=hf
Electrons in these atoms absorb photons and move to higher energy levels.
These absorbed wavelengths are missing from the spectrum, creating dark absorption lines.
Each element produces a unique pattern of absorption lines, allowing identification.
What is meant by the particle nature of light?
The idea that light behaves not just like a wave, but also as if it’s made up of particles called photons. This is part of the wave-particle duality in quantum physics.
Photons are discrete packets of energy
