2. Quantum Phenomena

Question 1

If you shine light of a high enough _______ onto the surface of a metal, it will emit electrons.

Answer 1

Frequency

Question 2

What is the photoelectric effect?

Answer 2

When electrons on the surface of a metal absorb enough energy from light to overcome bonds holding it to the metal, allowing it to be released.

Question 3

Define threshold frequency.

Answer 3

Minimum frequency required for electrons to be released from the surface of a metal.

Question 4

Does intensity of the radiation affect the maximum kinetic energy a electron has.

Answer 4

No, frequency does.

Question 5

The number of photo-electrons emitted per second is proportional to what?

Answer 5

the intensity of the radiation.

Question 6

What are the discrete packets of electromangentic waves Einstein suggested?

Answer 6

Photons

Question 7

What is the h in the equation: E = hf?

Answer 7

Planck’s constant

Question 8

A photon would transfer all its _____ to one specific electron.

Answer 8

energy.

Question 9

If one photon collides with a free electron, the energy the electrons will gain is equal to ____

Answer 9

hf

Question 10

Define work function.

Answer 10

The minimum amount of energy required to break the bonds holding the electrons to the atom and allow it to flee the metals surface.

Question 11

If the energy delivered by the photon is below the work function, what happens?

Answer 11

No electron emission

Question 12

What is the equations for threshold frequency?

Answer 12

frequency = work function/ planck’s constant

Question 13

What is the maximum kinetic energy equal to?

Answer 13

hf - work function

Question 14

is the kinetic energy dependent on the intensity of the radiation?

Answer 14

No as each electron only absorbs one photon at a time. Increasing the intensity just means more photons per second on an area, each photons have the same energy as before.

Question 15

Define stopping potential.

Answer 15

It is the p.d needed to stop the fastest moving electron.

Question 16

In an atom, where do the electrons exist?

Answer 16

In well-defined energy shells.

Question 17

How can electrons move down energy levels?

Answer 17

By emitting photons.

Question 18

The energy of each photon either emitted or absorbed must be equal to what?

Answer 18

Energy needed for the electron to transition to a different energy shell.

Question 19

How many joules are there in a electronvolt?

Answer 19

1.60 x 10^-19J

Question 20

Define the electronvolt.

Answer 20

The kinetic energy carried by an electron after it has been accelerated through a potential difference of 1V.

Question 21

Define excitation.

Answer 21

Movement of an electron to a higher energy level. This is done by the electron absorbing an photon which carries an amount of energy equal to the energy difference between the two energy shells.

Question 22

What does it mean if an atom becomes ionised?

Answer 22

An electron is removed from the atom, making the atom positively ionised.

Question 23

Define ionisation energy.

Answer 23

Amount of energy required to completely remove an electron from an electron from the atom from the ground state.

Question 24

What is the ground state?

Answer 24

Lowest energy level, nearest the nucleus.

Question 25

How is light produced in a fluorescent tube?

Answer 25

Free electrons collide with electrons in mercury atoms, causing them to excite to higher energy levels. These electrons then return to their original energy levels, releasing a UV photon. The phosphorus coating on the tube absorbs photons, exciting electrons to much higher orbits. These electrons cascade down the levels, emitting visible light photons.

Question 26

How is a light spectrum formed?

Answer 26

Light from fluorescent tubes hits prism or diffraction grating, creating a line spectrum.

Question 27

What is a light spectrum?

Answer 27

Series of bright lines against a black background. Each line corresponds to a particular wavelength of light emitted by the source.

Question 28

Why is white light described as continuous?

Answer 28

Contains all possible wavelengths. The colours all merge into each other - there is no gaps in the spectrum.

Question 29

Does hot or cold things emit a continuous spectrum in the visible and infrared?

Answer 29

Hot things.

Question 30

Are electrons confined to energy levels in objects producing a continuous spectrum?

Answer 30

No, electrons are not bound to the atom and are free.

Question 31

You get _____________ when light with a continuous spectrum of energy passes through a cool gas.

Answer 31

Line spectrum.

Question 32

At low temperature, most of the electrons in the gas atoms will be in their ________________.

Answer 32

Ground state.

Question 33

Why are certain wavelengths missing in a continuous spectrum when it comes out the other end of a cool gas.

Answer 33

The electrons absorb photons with a specific energies equal to the difference between two energy levels. Photons of the corresponding wavelength cause excitation of electrons. These wavelengths are missing from the continuous spectrum.

Question 34

Why is finding the line spectra useful?

Answer 34

Each element has its own unique line spectra like a barcode and so the element can be identified using this.

Question 35

___________ and ____________ show light as a wave.

Answer 35

Interference and diffraction.

Question 36

_____________ ________ shows light behaving as a particle.

Answer 36

Photoelectric Effect

Question 37

What was De Broglie Suggestion?

Answer 37

If wave-like light showed particle properties (photons), particles like electrons should be expected to show wave-like properties.

Question 38

What is the ‘mv’ in the de Broglie equation?

Answer 38

Mass x velocity which is the momentum.

Question 39

What observation can be used to show that electrons have a wave like nature.

Answer 39

Electron diffraction. Diffraction patterns are observed when accelerated electrons in a vacuum tube interact with the spaces in a graphite crystal.

Question 40

____________ the electron speed and the diffraction pattern squashes together towards the middle. This supports the de Broglie equation.

Answer 40

Increase

Question 41

An electron with a ___________ mass, makes the diffraction pattern more closely packed.

Answer 41

Greater