The Photoelectric Effect

Question 0

The light has to have a high enough …. In order for the …. To emit ….

Answer 0

Frequency
Metal
Electrons

Question 1

What does shining light on a metal release

Answer 1

Electrons

Question 2

What does (for most metals) this frequency fall within

Answer 2

The U.V. Range

Question 3

Describe in detail what happens when you shine light at a metal

Answer 3

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

Question 4

What are the 3 main conclusions we can draw from the photoelectric effect experiment

Answer 4

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

Question 5

What are the electrons emitted by shining light at a metal called

Answer 5

Photoelectrons

Question 6

What causes the value of the maximum kinetic energy a Photoelectron is emitted with to increase

Answer 6

Frequency of radiation

Unaffected by intensity

Question 7

What can’t the photoelectric effect be explain by

Answer 7

WAVE THEORY

Question 8

What 4 things does the WAVE THEORY state

Answer 8

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

Question 9

State the first reason why the WAVE THEORY must be wrong in relation to the PHOTOELECTRIC EFFECT

Answer 9

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

Question 10

State the second reason why the WAVE THEORY must be wrong in relation to the PHOTOELECTRIC EFFECT

Answer 10

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

Question 11

What did Einstein suggest about EM WAVES (and the energy they carry)

Answer 11

They can only exist in DISCRETE PACKETS

Question 12

What are these EM WAVES (and the energy they carry) which can only EXIST in DISCRETE PACKETS called

Answer 12

These WAVE-PACKETS are called PHOTONS

Question 13

What did Einstein see these photons as having

Answer 13

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

Question 14

What is the equation for the energy carried by one of these wave-packets (photons)

Answer 14

E=hf=hc/y

Question 15

What does the photon model say

Answer 15

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

Question 16

What is the energy needed by an electron to leave the surface and BREAK the BONDS holding it there called

Answer 16

WORK FUNCTION ENERGY (o/)

Question 17

What does the WORK FUNCTION ENERGY value depend on

Answer 17

The METAL

Question 18

How does the photon model explain THRESHOLD FREQUENCY

Answer 18

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

Question 19

What is the equation for threshold frequency

Answer 19

hf bigger than of equal to O/ (phil)

Question 20

In theory, what could happen if a second photo hit an electrons before the energy from the first was released

Answer 20

Could GAIN enough energy to leave metal

Would have to happen EXTREMELY QUICKLY-chances slim

Question 21

How does the photon model explain the maximum kinetic energy

Answer 21

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

Question 22

What’s the equation for the maximum kinetic energy

Answer 22

Maximum Ke= hf-O/

Question 23

Explain effect emitted electrons decreasing frequency incident radiation

Answer 23

Decrease energy carried photon

Decrease maximum kinetic energy

Question 24

Explain effect on emitted electrons of doubling intensity

Answer 24

Increase number photons per second

Double number emitted per second