Chapter 13: Quantum Physics

Question 1

How are EM waves released?

Answer 1

in discrete packets

Question 2

quanta

Answer 2

energy from waves released as lumps

Question 3

photon

Answer 3

discrete packets of waves

Question 4

how does a photon act?

Answer 4

like a neutral particle
either transfer all OR none of its energy when it interacts with another particle

Question 5

How do you calculate the energy of the photon?

Answer 5

E =hf
energy = planck’s constant x frequency

Question 6

what does a higher frequency in a photon mean?

Answer 6

it has more energy

Question 7

what happens when you accelerate an electron in a potential difference?

Answer 7

it transfers some electrical potential energy into kinetic energy

Question 8

what is the energy transfer equation?

Answer 8

eV = 0.5 x m x v2

Question 9

electronvolt

Answer 9

ke gained by an electron when accelerated through a PD of 1V

Question 10

How do you find Planck’s constant?

Answer 10

You need a monochromatic light, set up circuit with a ammeter, variable resistor, voltmeter and battery
1) set Variable Resistor to R(max), so there is no current
2) Adjust until current just begins to flow through
3) record voltage across LED, this is the threshold Voltage
4) Record wavelength of LED
5) Disconnect so circuit can cool
6) Repeat for consistency, then repeat for range of LEDs

Question 11

monochromatic light

Answer 11

single wavelength, single colour

Question 12

threshold voltage

Answer 12

voltage needed to give an electron the same energy as a photon emitted by an LED

Question 13

what happens at the threshold voltage?

Answer 13

Ke is equal to eV0, where V0 is the threshold voltage

Question 14

What happens when you shine a high enough frequency onto a metal surface?

Answer 14

metal ejects electrons, usually in the UV range

Question 15

Work function energy (φ)

Answer 15

energy needed for electrons to break metallic bonds and escape metal surface

Question 16

photoelectrons

Answer 16

the electrons emitted from the metal surface after a high frequency is shone onto it

Question 17

Photoelectric experiment (gold leaf electroscope)

Answer 17

1) zinc plate is given an negative charge
2) negatively charged repels negatively charge gold leaf, causing it to rise up
3) UV light is shone on the gold plate
4) Energy of light causes electrons to be lost from zinc by photoelectric effect
5) As all of the objects lose their negative charge, gold leaf is no longer repelled, falls back down

Question 18

What conclusions can be made from the photoelectric experiment?

Answer 18

1) For a given metal, no photoelectrons emitted if radiation frequency is below the threshold
2) photoelectrons emitted from a variety of Ke (0 to max); max increases if frequency of radiation increases
3) photoelectrons emitted per second is directly proportional to intensity of radiation

Question 19

what happens if the shone light on the metal has a low frequency?

Answer 19

it would take longer for the electrons to gain energy?

Question 20

what happens if the intensity of the shone light increases?

Answer 20

Rate of photoemission increases