Quantum

Question 1

What is the work function?

Answer 1

The minimum energy required for electrons to be liberated.

Question 2

What is the threshold frequency?

Answer 2

The minimum frequency of light photons required to get the work function, using E=hf (The photoelectric effect)

Question 3

What happens if the frequency is less than the threshold frequency?

Answer 3

No electrons are liberated

Question 4

What happens if the frequency equals the threshold frequency?

Answer 4

Electrons are liberated but with no kinetic energy

Question 5

What happens if frequency is greater than the threshold frequency?

Answer 5

Electrons are liberated with kinetic energy

Question 6

How does intensity affect the liberation of electrons?

Answer 6

If f is less than threshold frequency then it has no effect as no electrons can be liberated as there is not enough energy. If frequency is greater than or equal to the threshold frequency increasing the intensity increases the number of electrons liberated

Question 7

What is the photoelectric effect equation?

Answer 7

Work function = h x threshold frequency

Therefore,

hf = work function+ max KE

Question 8

On a graph of kinetic energy against frequency, what is the y-intercept?

Answer 8

The work function

Question 9

On a graph of kinetic energy against frequency, what is the x-intercept?

Answer 9

Threshold frequency

Question 10

On a graph of kinetic energy against frequency, what is the gradient?

Answer 10

h, Planck’s constant

Question 11

In wave-particle duality, what gives evidence for waves acting as waves?

Answer 11

Reflection, refraction, diffraction

Question 12

In wave-particle duality, what gives evidence for waves acting as particles?

Answer 12

The photoelectric effect

Question 13

In wave-particle duality, what gives evidence for particles acting as waves?

Answer 13

Electron diffraction

Question 14

In wave-particle duality, what gives evidence for particles acting as particles?

Answer 14

Classical (eg Newtonian) Physics

Question 15

What is the De Broglie wavelength?

Answer 15

Every moving particle with mass will have an associated wavelength:

Wavelength = h/p = h/mv

Question 16

What name is given to the first energy level?

Answer 16

Ground state

Question 17

What are absorption spectral lines?

Answer 17

Black lines that show where energy has been absorbed from during excitation

Question 18

What do emission spectral lines show?

Answer 18

Coloured lines show the photons of certain frequencies emitted during de-excitation.

Question 19

Define 1 Joule.

Answer 19

1 joule of energy is transferred when 1 coulomb of charge passes through a potential difference of 1 volt

Question 20

Define 1 election volt.

Answer 20

The energy for 1 electron to pass through a potential difference of 1 volt

Question 21

How does the amount of energy change as you move further from the ground state?

Answer 21

It increases

Question 22

Explain excitation by photon absorption

Answer 22

1. A photon passed through an electron in the atom
2. The electron only absorbs the photon if it has the exact right amount of energy needed to excite
3. If the photon has the correct energy, the electron absorbs it and moves
4. If the photon does not have the right amount of energy, it passes through and the electron remains in the same state

Question 23

Explain excitation by electron collision.

Answer 23

1. A free electron collides with an electron in an atom
2. The electron in the atom absorbs the amount of energy it needs to move energy levels from the moving electron
3. The electron in the atom moves
4. The free electron is rebounded if it has remaining energy

Question 24

Explain de-excitation.

Answer 24

Electrons need to be on the lowest possible energy level
If there is a space on a lower energy level after another electron has been excited or liberated, the electron will move down to the lower level, emitting a photon of energy as it moves
The photons frequency depends on the amount of energy released in order to move

Question 25

What is an example of a use of electron excitation?

Answer 25

Fluorescent lamps

Question 26

How does a fluorescent lamp work?

Answer 26

1. Fluorescent substances have UV sensitive pigments (phosphor)
2. An electric current is passed through a fluorescent lamp, electrons in the current collide with atoms of mercury vapour in the lamp
3. The electrons must have sufficient energy for the collisions to excite the electrons in the mercury
4. When the mercury electrons de-excite, they emit UV photons
5. The tube is coated in a phosphor which will absorb the photons, exciting their electrons
6. When these electrons de-excite they emit photons of visible light

Question 27

What is the maximum kinetic energy during the photoelectric effect?

Answer 27

Ek max is the maximum kinetic energy of the photoelectrons

Question 28

What is an ion?

Answer 28

an atom which has the same number of protons and neutrons in the nucleus but has gained or lost an electron from its orbital to become positively or negatively charged

Question 29

How many joules is 1 electron volt?

Answer 29

1.6x10^-19

Question 30

What do the lines on spectra correspond to?

Answer 30

the discrete energy levels of the atom

Question 31

Why does momentum affect the diffraction pattern produced?

Answer 31

smaller momentum will result in a longer wavelength. The diffraction or spread of a wave passing through a slit depends on the wavelength- the longer the wavelength, the more the light spreads out. electrons with smaller momentum will produce a more diffuse diffraction pattern

Question 32

What were the 2 opposing greek views of how matter was formed and which was more believed? (and explain each)

Answer 32

1. Democritus’s “atomos” theory that everything was made up of small indivisible atomos. by mixing different atomos you could make different materials.
2. Aristotle’s Alchemy theory that everything was made of the four elements - earth wind fire and water.
   Aristotle’s theory was preferred for approx 2000 years.

Question 33

What was John Dalton’s theory of how matter was formed, and in which year was it hypothesised?

Answer 33

in 1808, he said matter was made of elements, which were pure substances which contained no other elements. he said each element was made of a different type of atom. he created the “billiard ball” model as he said atoms were tiny solid spheres.

Question 34

What did J.J Thomson hypothesise?

Answer 34

in 1987 J.J Thomson said the atom was a positively charged sphere with negatively charged electrons embedded within it. this was the first mention of subatomic particles. (“plum pudding” model)

Question 35

Explain Rutherford’s gold foil experiment.

Answer 35

Rutherford shot positively charged alpha particles at a sheet of gold foil. He detected the number of particles to pass through the foil. he discovered, while most passed straight through, some were partially deflected and others completely rebounded. this all took place in a vacuum as not to be disturbed by air particles,

Question 36

What did Rutherford propose from the results of his experiment?

Answer 36

the atom was mostly empty space with a positively charged centre which he named the nucleus. and the electrons must orbit the nucleus

Question 37

What must be done for a scientific theory to be valid?

Answer 37

it must have repeatable experimental results supporting the hypothesis