Quantam Flashcards
(15 cards)
1
Q
what is the photoelectric effect?
A
when em radiation falls on a negatively charged piece of metal, the electrons might gain enough energy and escape
2
Q
what are the two factors which determine if they escape or not?
A
- the frequency of the em radiation
- the work function of the metal
3
Q
what is the work function?
A
- the energy an electron needs to escape from the surface of the metal
- (more reactive metals = smaller work functions)
4
Q
what is em radiation made up of?
A
photons
5
Q
what does the energy of a photon depend on?
A
its frequency
6
Q
greater intensity =
A
more photons
7
Q
the photoelectric equation
A
hf = Φ + Ek max
8
Q
h =
A
6.63 x 10^-34 Js
9
Q
hf =
A
energy of the photon
10
Q
Φ =
A
work function of the metal
11
Q
Ek max =
A
max kinetic energy of the escaped electrons
12
Q
what is excitation?
A
an electron jumps from a lower level to a higher level
13
Q
what is emission?
A
- an electron falls from a higher level to a lower level
- thus, the energy of the photon is equal to the difference between the energy levels
14
Q
1eV =
A
1.6 x 10^-19 J
15
Q
how do fluorescent tubes work?
A
- a large voltage is put across the tube
- electrons are emitted from the cathode
- these electrons ionise some mercury atoms producing even more electrons
- these electrons excite other mercury atoms
- the mercury atoms emit UV light
- the UV light excites atoms in the fluorescent powder to very high energy levels
- as these electrons fall down the energy levels many different visible colours are emitted so the tube appears to emit white light
