Quantum

Question 1

What is a quantum?

Answer 1

A single packet of EMM radiation

Question 2

Give the two different equations of the energy carried by a quanta

Answer 2

E=hf=hc/wavelength
H equals the plank constant and see equals the speed of light in a vacuum

Question 3

What charge do photons have?

Answer 3

They don’t have any charge

Question 4

What did Einstein suggest

Answer 4

He suggested that EM waves can only exist in discreet packets which are photons

Question 5

What is the unit of a photon and what is that definition?

Answer 5

The electronvolt
It is the kinetic energy gained by an electron when it is accelerated to a potential different of one volt
Electro volt= eV

Question 6

How can you find the plank constant using LEDs?

Answer 6

Connect an LED in series with a milli ammeter and a variable resistor
Then connect a voltmeter parallel to the LED
Use different coloured LEDs with different known wavelengths
Start off with zero current through the circuit and then adjust the variable resistor so that the current just begins to flow through the second and the LED lights up this voltage across the LED
Repeat this for different colours LEDs with different wavelengths
The threshold voltage need to give the electrons the same energy as a photon emitted by the LED therefore all the electrons kinetic energy energy is accelerated. This potential is then transferred into a photo therefore we can use the equation eV=hc/wavelength
You can rearrange this equation and then plot graph of voltage against one over wavelength so that the gradient is hc/e

Question 7

Describe what happens with a gold leaf electroscope

Answer 7

The gold leaf electroscope is a box with a glass window and a gold leaf inside attached to a zinc plate which is placed on the top of the box
Initially the electroscope plate is negatively charged therefore the gold leaf is repelled. However as you shine ultraviolet light onto the zinc plate the photoelectric effect causes its free electrons to be ejected. This causes the metal to lose its negative charge and the gold leaf is no longer repelled and drop down.

Question 8

State the conclusions from the gold leaf electroscope experiment

Answer 8

For a given metal no photon electrons are admitted if the radiation has a frequency below a certain value which is called the threshold frequency
The electrons are admitted with a variety of kinetic energies ranging from 0 to maximum value this value of maximum kinetic energy increases with the frequency of the radiation however it is unaffected by the intensity
The number of electrons admitted per second is proportional to the intensity of the radiation

Question 9

What does the photo Electric affect prove

Answer 9

It proves the particulate nature of radiation

Question 10

What can we say about the interaction between electrons and photons during the photo? Electric effect?

Answer 10

It is a one-to-one interaction between a photon and an electron therefore three electrons cannot interact with one photon vice versa

Question 11

Why does visible light not release the gold leaf even when the intensity is delight is increased?

Answer 11

When using visible light no electrons are admitted as the photon energy is below the work function of the metal and even if we increase the intensity of visible light meaning more photons there will still be no electrons admitted as there is only a one-to-one interaction between electrons and photons

Question 12

What happens when a UV light is used on the gold leaf experiment?

Answer 12

UV light has photons with a greater energy than the work function of the metal therefore photo electrons are admitted and the gold leaf drops
Bringing the source closer will increase the intensity therefore more electrons are emitted

Question 13

What happens if glass is inserted in front of the UV source Indigo leaf experiment

Answer 13

No electrons will be admitted as the glass will absorb the UV light

Question 14

How does the photoelectric affect prove that the radiation has particle nature?

Answer 14

The electron emission is instantaneous

Question 15

How do we convert electron volt into joules

Answer 15

Multiplied by the elementary charge

Question 16

Explain why during the photo Electric effect the frequency of the EEM radiation must be above a minimum value for electrons to be released

Answer 16

At minimum value the work function is greater than the energy of the photons as the energy of the photons is proportional to the frequency of radiation therefore as the frequency increases the energy of the photons will also increase

Question 17

When given a graph of EK against frequency, how do you find the work function of the metal?

Answer 17

Extend the graph down until it has a white intercept, which is the negative answer

Question 18

J explain why the wave theory of light is unable to explain the photo Electric effect

Answer 18

If the wave nature of light was correct incident radiation will always lead to the release of an electron even if the frequency of the radiation was very low. This means the electron may take longer to be released but it will be released once it has absorbed enough energy, however this is not correct as For the electron to be admitted requires a threshold frequency
If the wave of nature of light was true, the intensity of light would affect the kinetic energy of the electrons that was released as the radiation would have more energy to transfer to the electrons on the surface of the matter however the intensity of light has no effect on the kinetic energy or the work function

Question 19

State the conclusions that can be made from the photo Electric experiment

Answer 19

The number of electrons released is directly proportional to the intensity of the incident radiation if the source has a high frequency than the threshold frequency
The frequency of the incident radiation is below the threshold frequency of the metal then no electrons are admitted
The electrons released have a range of kinetic energies which are dependent upon the frequency of the incident radiation
Each metal has an individual wave function

Question 20

Describe and explain the photoelectric effect

Answer 20

The photo Electric effect is the emissions of electrons from the surface of a metal surface when the EEM radiation is above the threshold frequency of the metal
One photon is absorbed by one electron on the surface of the metal if the frequency of the photon is higher than the threshold frequency it can overcome the work function of the metal and be admitted from the surface of the metal
The work function is the minimum energy required for an electron to be released from the surface of a metal
High intensity of light will result in the admissions of more photo electrons
Protons with a higher energy will result in the emissions of electrons with a higher kinetic energy

Question 21

Describe and explain what affects doubling the intensity of the incident light will have on the photo Electric current

Answer 21

Doubling the intensity of radiation will double the number of electrons admitted due to the one-to-one nature of the photoelectric effect therefore as current is the flow of electrons the photo Electric current will also double

Question 22

State the impact that the photoelectric effect had on the previous light theories

Answer 22

The electric effect proved that light was made of particles called photons and was not purely wave

Question 23

Describe an explained a piece of evidence for the wave nature of electrons

Answer 23

Electron diffraction where electrons travelling through graphite which has an atomic spacing approximately equal to thede broglie wavelength of the electrons causing an interference pattern consisting of interference fringes which are rings
Changes in the electrons energy changes the size of ring therefore the interference ring spacing

Question 24

Explain what is meant by the wave particle duality of light

Answer 24

It has both wavelike and particlelike properties

Question 25

Explain why a polycrystalline graphite sample is used during the electron diffraction

Answer 25

The atomic spacing of the polycrystalline graphite sample is similar to the wavelength of the light. This causes maximum diffractions of the electrons which leads to them interfering.

Question 26

Is it possible to observe larger object (larger than a neutron) to diffract through a silicon crystal

Answer 26

Larger objects have smaller de bregolie wavelengths, and no gaps are smalll enough to match the wavelength to allow diffraction

Question 27

How do you fi d KE using photon enrgy and work function

Answer 27

Photon - work = max KE

Question 28

State the photoelectric effect

Answer 28

The emissions of electron from the surface of a metal when EM waves are incident on metal

Question 29

State three statements about photons

Answer 29

They are electrically neutral
The speed of photons changes between the boundary of air and glass
The energy of a photon depend on its wavelength

Question 30

The photoelectric effect cannot be explained in the terms of wave-model of em waves.
Discuss new knowledge of the particulate nature of waves that was used by physics to validate the photon model

Answer 30

The wave model cannot explain why there is a threshold frequency for metals
The new model showed the one to one interaction between electrons and photon which proves the existence of threshold frequency
It also showed that energy of a photon must be greater than or equal to the work function of the metal

Question 31

State the change, if any, on the energy of photon when intensity is doubled

Answer 31

The enrgy depends of wavelength or frequency therefore intensity ones not change

Question 32

What happens to the interference pattern when the electrons speed increases

Answer 32

The interference pattern is closer together and is brighter

Question 33

Link the conservation of energy with quantum physics

Answer 33

Energy of photon= work function + KEmax

Question 34

Equation for threshold frequency

Answer 34

F=h/ work function