Chapter 17- Particle Nature Of Light

Question 1

What is newton’s corpuscular theory?

Answer 1

He thought of light as being made up of corpuscles (or tiny particles)

He imagined the particles to bounce of the surfaces explaining reflection

Question 2

What was Huygen’s wave theory?

Answer 2

Light consisted of waves like ripples spreading out like a stone dropped in water

Question 3

Difference between Huygen’s or newton’s theories?

Answer 3

The differences in our if water or glass and then in air which medium means light has the fastest speed

Question 4

Intensity def

Answer 4

The power per unit area

Has units W m^-2

Question 5

Another way of saying intensity

Answer 5

Radiation flux density

Question 6

Intensity eq

Answer 6

Intensity = power/area

Question 7

If we are a distance r from point source of radiation, what will happen to the radiation?

Answer 7

It will spread out in all directions over a sphere of surface area 4pie r^2

Question 8

The photoelectric effect can be demonstrated by what means?

Answer 8

A negatively charged zinc plate and a UV lamp

Question 9

What happens in photoelectric effect?

Answer 9

The freshly cleaned zinc plate is given a negative charge
Under visible light photoelectrons are discharged at a very low rate
But under slight UV light they are discharged immediately

Question 10

If zinc plate is positively charged what happens with the photoelectric effect?

Answer 10

Nothing at all

As any photoelectrons transmitted would be attracted to the plate

Question 11

What is the photoelectric effect?

Answer 11

When energy from the light is given to the electrons causing their emission from the substance

Question 12

If ONE photon had enough energy then…

Answer 12

It will release ONE photoelectron

Question 13

What is a quanta now called

Answer 13

A photon

Question 14

What is a quanta formed from

Answer 14

Discrete bundles of energy

Question 15

Instead of energy from the light being gradually absorbed by the electrons near the surface….

Answer 15

Einstein reasoned that

The electron would be emitted only if a single quantum of the light had enough energy for the electron to escape

Question 16

What is Einsteins theory called?

Answer 16

Quantum theory

Question 17

Why can UV discharge a photoelectron and visible light can’t?

Answer 17

Because UV has a higher frequency than visible light

Question 18

The intensity of a light source depends on… (2)

Answer 18

The number of quanta

The energy associated with each quantum

Question 19

Electron volt def

Answer 19

The work done on (or gained by) an electron when it moves through a potential difference of 1 volt

Question 20

Electron volt unit

Answer 20

eV

Question 21

1 electron volt has how many joules of energy?

Answer 21

1.6 x10 ^-19 J

Question 22

What is the bare minimum energy needed to liberate an electron from the surface called?

Answer 22

The work function

Symbol= o with line through it

Question 23

If a photon of energy hf has more than the work function what does it go into

Answer 23

Kinetic energy

Question 24

maximum kinetic energy an electron can have eq

Answer 24

hf= 🚫+ 1/2 mvmax^2

Question 25

What is Einsteins photoelectric eq

Answer 25

hf= 🚫+ 1/2mvmax^2

Question 26

Electrons are emitted with a range of kinetic energies up to the maximum because...

Answer 26

Because electrons inside the metal will need more than the work function to escape

Question 27

There will be no photoelectric emission unless...

Answer 27

hf>🚫

Question 28

Threshold frequency

Answer 28

Frequency just large enough to liberate electrons fo So 🚫=hfo

Question 29

What is a phototube?

Answer 29

Name given to a type of photocell that generates photoelectrons when light falls on a specifically coated metal cathode

Question 30

What is a photovoltaic photocell?

Answer 30

In which an emf is generated by the presence of light across the boundary of two semiconducting materials, the photoconductive cells, or LDRs

Question 31

Ground state def

Answer 31

The state an electron is in when it is at its lowest possible energy level

Question 32

Ionisation energy def

Answer 32

The energy that must be supplied for an electron in the lowest energy level to just escape from the atom

Question 33

Quantum DEFINITION

Answer 33

A fixed or discrete amount of energy

Question 34

Emission spectrum def

Answer 34

Of a chemical element or compound, is the spectrum of frequencies of electromagnetic radiation emitted when the electrons in an atom make a transition from a high energy state to a lower-energy state

Question 35

When an electron drops from energy level E2 to a level E1 eq

Answer 35

hf= E2 - E1

Question 36

Applications of quantum emission (2)

Answer 36

* radar (radio detection and ranging) | * laser

Question 37

What happens in an absorption spectrum?

Answer 37

Radiation is absorbed by a substance at frequencies that match the energy difference between two quantum states of electrons in an atom or molecule of the substance

Question 38

What is wave-particle duality?

Answer 38

The concept describing the fact that light behaves like waves and also like a particle

Question 39

What is Broglie's wave-particle duality eq?

Answer 39

Wavelength= h/p (momentum)

Question 40

What is the complementarity principle?

Answer 40

Says that sometimes electrons have the properties of particles and sometimes the properties of waves, but never both together

Question 41

What is plank's constant

Answer 41

6.63 x10 ^-34

Question 42

Energy eq

Answer 42

E= hf

Question 43

Kinetic energy max eq

Answer 43

KE= hf- 🚫o

Question 44

Stopping potential def

Answer 44

Point of frequency at which no flow is created as all photoelectrons released are then attracted back to the original cathode as they run out of energy

Question 45

Stopping potential eq

Answer 45

Vs x charge = E Therefore.. qVs= hf- 🚫o = KE max

Question 46

Charge of an electron

Answer 46

1.6 x10 ^-19

Question 47

Alternative eq to | KE= hf- 🚫

Answer 47

KE= hc/wavelength - 🚫

Question 48

Electric fields cause

Answer 48

Voltages

Question 49

A photon can be emitted in

Answer 49

Any direction | Fewer photons therefore come back towards you (intensity decreased)

Question 50

You can tell the type of elements something is made up from by...

Answer 50

The absorption spectrum

Question 51

What type of emission when dropping down energy states

Answer 51

Spontaneous emission

Question 52

Mass of an electron

Answer 52

9.1x10 ^-31