5.5 Photoelectric effect and Atomic Spectra

Question 1

What’s the photoelectric effect?

Answer 1

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

Question 2

What’s the work function, Φ

Answer 2

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

Question 3

What is f, in hf=Φ +1/2 x mv^2?

Answer 3

As Φ is the minimum energy required, f is the threshold frequency (minimum frequency required)
E(Φ)=h x threshold frequency

Question 4

How does intensity of the light effect the photoelectric effect?

Answer 4

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

Question 5

What’s the gold leaf electroscope experiment?

Answer 5

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

Question 6

How do electrons sit in atoms?

Answer 6

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

Question 7

What’s the atomic spectra?

Answer 7

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

Question 8

Why do dark absorption lines appear in a star’s spectrum?

Answer 8

A star emits a continuous spectrum of light.
Elements 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.