Quantum physics

Question 1

Photoelectric emission

Answer 1

instantaneous process refers to the emission of electrons when the surface of a metal is exposed to light/EMR.

Question 2

Define photon

Answer 2

photon is a packet of EMR possessing a fixed amount of energy

Question 3

Define eV

Answer 3

eV is an alternate unit of energy and is defined as the amount of kinetic energy gained by an electron if it accelerates from rest through a p.d of 1 volt

Question 4

define work function energy

Answer 4

energy of photon to cause the emission of electron from surface with zero kinetic energy

Question 5

define threhold frequency

Answer 5

defined as the minimum frequency required to bring the electron to the surface.

Question 6

Why a certain frequency of EMR will allow emission of electrons?

Answer 6

when appropriate frequency is incident on the metal surface one part of the energy is used up in overcoming the work function while the remaining is converted into kinetic energy of emitted electrons.

Question 7

How to ensure that the electrons will be emitted?

Answer 7

1) when workfunction energy is less than the energy of a photon.
2) incident frequency is more than threshold frequency.

Question 8

Why emitted electrons will have a range of kinetic energy.

Answer 8

Not all electrons are present on the surface, those electrons which are embedded within the surface might have to use some of their energy to reach the surface before they can be emitted hence they will br emitted with kinetic less than the max value.

Question 9

Define stopping potential

Answer 9

refers to voltage of the battery applied in oppossite directions which causes the photoelectric current to become zero.

Question 10

define intensity.

Answer 10

Intensity is the total power falling on a metal surface per unit area

Question 11

Describe what would happen when intensity of a photon is increased but freq is kept constant.

Answer 11

when intensity is increased more number of photons will reach the metal surface and more number of electrons will be released thus photoelectric current increases.

Question 12

whichproperty of EMR is proven by photoelectric emission?

Answer 12

the dual nature of EMR

Question 13

Which properties prove that EMR can behave as particles.

Answer 13

1) process is instantaneous

2) occured when incident frequency is greater than threshold frequency.

Question 14

Which properties of EMR can prove they can behave as waves.

Answer 14

1) interference
2) superposition
3) diffraction.

Question 15

Describe an experiment which can prove that electrons also exhibit dual nature.

Answer 15

when electrons strike the flourescent screen equally spread bright spots of lights are observed which prove that kinetic energy is converted to light energy.

electrons will spread out and undergo diffraction as they pass the carbon film.

Question 16

why do each atom/element have discrete emission spectra?

Answer 16

Since only certain wavelength and frequencies are absorbed for the electron to move from a higher energy level to a lower energy level. hence electrons in atoms can only transition between discrete energy levels.

Question 17

describe the absorption spectra

Answer 17

When light is passed through the glass chamber which contains the hydrogen gas some wavelength of light will pass right through the glass and would appear as high intensity regions on the screen.

however those wavelengths which were absorbed by the electron would cause the elctron to transit to a higher energy level but due to the unstability of the electron at high evergy levels the elctron comes down to a lower energy level and would emit the wavelength it had absorbed in all directions. thus low intensity regions are formed which appear as dark lines on the screen.

Question 18

Define Debroglie wavelength

Answer 18

wavelength associated with a particle that is moving.

Question 19

threhold wavelength

Answer 19

longest wavelength of incident EMR that would remove a photoelectron from the surface of a metal