The Photoelectric Effect Flashcards
The light has to have a high enough …. In order for the …. To emit ….
Frequency
Metal
Electrons
What does shining light on a metal release
Electrons
What does (for most metals) this frequency fall within
The U.V. Range
Describe in detail what happens when you shine light at a metal
FREE ELECTRONS on the surface of the metal, ABSORB energy from the light making them VIBRATE
If AN ELECTRON ABSORBS enough energy, the BONDS holding it to the metal BREAK and the electron is released
Fe,abvi, Ae,ab, bobr
What are the 3 main conclusions we can draw from the photoelectric effect experiment
1) no photoelectrons emitted if RADIATION below THRESHOLD FREQUENCY
2) photoelectrons are emitted with a VARIETY OF KINETIC ENERGIES (ranging 0-maximum value)
3) NUMBER of photo electrons emitted per second PROPORTIONAL to INTENSITY of radiation
What are the electrons emitted by shining light at a metal called
Photoelectrons
What causes the value of the maximum kinetic energy a Photoelectron is emitted with to increase
Frequency of radiation
Unaffected by intensity
What can’t the photoelectric effect be explain by
WAVE THEORY
What 4 things does the WAVE THEORY state
1) for a particular FREQUENCY of light, the ENERGY carried is PROPORTIONAL to the INTENSITY of the beam
2) energy carried SPREAD EVENLY over wavefront
3) EACH FREE ELECTRON would gain a BIT of energy from EACH incoming wave
4) gradually, each electron gain ENOUGH energy to leave metal
State the first reason why the WAVE THEORY must be wrong in relation to the PHOTOELECTRIC EFFECT
If the light had a LOWER FREQUENCY
I.e. carrying LESS ENERGY
Take LONGER for electrons to gain enough energy
But would EVENTUALLY happen
No explanation for threshold frequency
State the second reason why the WAVE THEORY must be wrong in relation to the PHOTOELECTRIC EFFECT
The higher the INTENSITY of the wave
The more ENERGY it should transfer to each E
The KINETIC energy should increase with INTENSITY
There is no explanation for the KINETIC ENERGY depending ONLY on the frequency
What did Einstein suggest about EM WAVES (and the energy they carry)
They can only exist in DISCRETE PACKETS
What are these EM WAVES (and the energy they carry) which can only EXIST in DISCRETE PACKETS called
These WAVE-PACKETS are called PHOTONS
What did Einstein see these photons as having
A ONE-ON-ONE
PARTICLE-LIKE interaction
with an electron in a metal surface
It would transfer ALL it’s ENERGY
To that ONE, SPECIFIC ELECTRON
What is the equation for the energy carried by one of these wave-packets (photons)
E=hf=hc/y
What does the photon model say
When light hits its surface, the metals BOMBARDED by photons
If one of these photons COLLIDES with a free electron- gain energy equal to hf
What is the energy needed by an electron to leave the surface and BREAK the BONDS holding it there called
WORK FUNCTION ENERGY (o/)
What does the WORK FUNCTION ENERGY value depend on
The METAL
How does the photon model explain THRESHOLD FREQUENCY
If energy gained from photon GREATER than WFE, the electron is EMITTED
If isn’t, SHAKE about a bit, then release energy as another PHOTON
Metal will HEAT UP but NO electrons emitted
What is the equation for threshold frequency
hf bigger than of equal to O/ (phil)
In theory, what could happen if a second photo hit an electrons before the energy from the first was released
Could GAIN enough energy to leave metal
Would have to happen EXTREMELY QUICKLY-chances slim
How does the photon model explain the maximum kinetic energy
Energy transferred to an electron is hf
KINETIC energy it will be carrying LEAVES hf-energy lost way out (explains range of energies)
The MINIMUM amount of energy it can lose is the WFE
The kinetic energy of the ELECTRONS is INDEPENDENT of the INTENSITY as it can only absorb 1 PHOTON at a time
What’s the equation for the maximum kinetic energy
Maximum Ke= hf-O/
Explain effect emitted electrons decreasing frequency incident radiation
Decrease energy carried photon
Decrease maximum kinetic energy
Explain effect on emitted electrons of doubling intensity
Increase number photons per second
Double number emitted per second
