Unit 1: Quantum Phenomena

Question 0

When does photoelectric emission not take place?

Answer 0

When the frequency of the incident electromagnetic radiation is below a certain value known as the threshold frequency and the wavelength of the incident light must be less than a maximum value equal to the speed of light divided by the threshold frequency.

Question 1

What is known as the photoelectric effect?

Answer 1

When electrons are emitted from the surface of a metal as electromagnetic radiation above a certain frequency is directed at the metal.

Question 2

What does threshold frequency depend on?

Answer 2

The type of metal.

Question 3

What doesn’t matter if the frequency of the incident radiation is smaller than the threshold frequency?

Answer 3

The intensity of the radiation.

Question 4

What is proportional to the intensity of the incident radiation?

Answer 4

The number of electrons emitted per second.

Question 5

How fast does the photoelectric prevail?

Answer 5

As soon as the incident radiation is directed at the metal (without delay) no matter how weak the intensity.

Question 6

What can the wave theory of light not explain?

Answer 6

The existence of the threshold frequency or why the photoelectric effect occurs without delay.

Question 7

What did wave theory incorrectly predict about the photoelectric effect?

Answer 7

Emission should take place with waves at any frequency and emission would take longer when using low intensity waves.

Question 8

What is light composed of?

Answer 8

Photons

Question 9

What is the formula for the energy of a photon?

Answer 9

Hf

Question 10

What is the equation for wavelength?

Answer 10

C/f

Question 11

What happens when light shines onto a metal surface?

Answer 11

An electron at the surface absorbs a single photon from the incident light and therefore gains energy equal to hf.

Question 12

When can an electron leave a metal surface?

Answer 12

If the energy gained from a single photon exceeds the work function of the metal.

Question 13

What is the work function?

Answer 13

The minimum energy needed by an electron to escape from the metal surface.

Question 14

What is the formula for the maximum kinetic energy of an emitted electron?

Answer 14

Ekmax = hf - work function

Question 15

What is the formula for the threshold frequency of a metal?

Answer 15

Fmin = work function/h

Question 16

The energy of each vibrating atom is…

Answer 16

Quantised meaning only certain levels of energy are allowed.

Question 17

What happens when the energy of the photon exceeds the work function?

Answer 17

The conduction electron can leave the metal.

Question 18

What happens if the electron does not leave the metal?

Answer 18

It collided repeatedly with other electrons and positive ions and it quickly loses its extra kinetic energy.

Question 19

What happens when light is directed at the photocathode?

Answer 19

Electrons are emitted from the cathode to the anode.

Question 20

What is proportional to the number of electrons per second that transfer from the cathode to the anode?

Answer 20

The reading on the ammeter.

Question 21

What is the equation for the number of photoelectrons that transfer from the cathode to the anode?

Answer 21

I/e where I is the photoelectric current and e is the charge of an electron.

Question 22

What is the photoelectric current proportional to?

Answer 22

The intensity of the light incident on the cathode.

Question 23

What is light intensity a measure of?

Answer 23

The energy per second carried by the incident light.

Question 24

What doesn't the intensity of the incident light affect?

Answer 24

The maximum kinetic energy of a photoelectron.

Question 25

How is Ekmax = hf - work function similar to y=mx+c

Answer 25

Y=Ekmax, h=gradient, x-intercept=threshold frequency and y intercept=-work function

Question 26

What is the process of creating ions (charged atoms) called?

Answer 26

Ionisation

Question 27

What is the equation for the ionisation energy of a gas atom?

Answer 27

eV

Question 28

What is the electron volt?

Answer 28

A unit of energy equal to the work done when an electron is moved through a pd of 1 volt.

Question 29

What is excitation?

Answer 29

This is when atoms can absorb energy from colliding electrons without being ionised.

Question 30

What do the certain energies that excitation can occur at link to?

Answer 30

The atoms of the gas.

Question 31

What happens if a colliding electron loses all its kinetic energy when it causes excitation?

Answer 31

The current due to the flow of electrons through the gas is reduced.

Question 32

What happens if the colliding electron does not have enough kinetic energy to cause excitation?

Answer 32

It is deflected by the atom with no overall loss in kinetic energy.

Question 33

What are excitation energies?

Answer 33

The energy values at which an atom absorbs energy.

Question 34

What happens when excitation occurs?

Answer 34

The colliding electron makes an electron inside the atom move from an inner shell to an outer shell.

Question 35

What is the excitation energy always less than?

Answer 35

The ionisation energy

Question 36

Is the energy of an electron in a shell constant?

Answer 36

Yes

Question 37

Which electrons have the most energy?

Answer 37

Those that are furthest from the nucleus.

Question 38

What is the ground state?

Answer 38

The lowest energy state of an atom.

Question 39

What is the excited state?

Answer 39

When an atom in the ground state absorbs energy and one of its electrons moves to a shell of higher energy.

Question 40

Why is the electron configuration in an excited atom unstable?

Answer 40

An electron that moves to an outer shell leaves a vacancy in the shell it moved from.

Question 41

What happens when an electron emits a photon?

Answer 41

An electron moves to an inner shell to fill in a vacancy. The atom therefore moves to a lower energy level.

Question 42

What is the energy of a photon equal to in excitation?

Answer 42

The energy lost by the electron and therefore the atom.

Question 43

What is the equation for the energy of an emitted photon?

Answer 43

E1-E2 (E1=higher energy level)

Question 44

What is the condition for an electron to absorb a photon and move to an outer shell?

Answer 44

The energy of the photon must exactly equal the gain in the electron's energy.

Question 45

Why does a fluorescent tube emit visible light?

Answer 45

Ionisation and excitation of the Mercury atoms occurs as they collide with each other and with electrons in the tube. The Mercury atoms emit UV photons when they de-excite, the UV atoms are absorbed by atoms of the fluorescent coating which causes excitation of the atoms and then the coating atoms de-excite and emit visible photons.

Question 46

Is a fluorescent tube more efficient than a filament lamp?

Answer 46

Yes

Question 47

Are wavelengths of the lines of a line spectrum of an element characteristic to the atoms of that element?

Answer 47

Yes

Question 48

Why do elements not produce the same pattern of light wavelengths?

Answer 48

The energy levels of each type of atom are unique to that atom.

Question 49

What is proof for the wave-like nature of light?

Answer 49

When diffraction of light takes place.

Question 50

What causes greater diffraction?

Answer 50

A narrower gap or a longer wavelength.

Question 51

When is the particle-like nature of light observed?

Answer 51

The photoelectric effect.

Question 52

Do matter particles have a dual wave-particle nature?

Answer 52

Yes

Question 53

What evidence is there that matter has particle-like properties?

Answer 53

Electrons in a beam can be deflected by a magnetic field.

Question 54

What evidence is there for matter having wave-like behaviour?

Answer 54

The de Broglie wavelength and the diffraction of electrons.

Question 55

What is the equation for the de Broglie wavelength?

Answer 55

H/p where p is momentum