Quantum Physics

Question 1

Photon

Answer 1

A quantum of electromagnetic radiation with energy equal to hf

Question 2

Explain the effect of maximum kinetic energy if the intensity of radiation remains constant while incident wavelength is reduced

Answer 2

Photon energy is larger hence the maximum kinetic energy of photo electrons is larger

Question 3

X-ray effect and photoelectric effect

Answer 3

in x-ray emission, electrons is used to generate photons, in photoelectric effect, photons are used to generate electrons

Question 4

Minimum wavelength for emitted x-rays

Answer 4

Maxiumum energy is lost in a single interaction when electrons
corresponding to the minimum wavelength

Question 5

Minimum wavelength for emitted x-rays

Answer 5

Maximum energy is lost in a single interaction when electrons
corresponding to the minimum wavelength

Question 6

photoelectric effect

Answer 6

1) Photoelectric effect is the emission of photoelectrons
2) from a metal surface
3) when light (or
electromagnetic radiation)
4) above a minimum threshold frequency strikes it.

Question 7

Work function

Answer 7

The work function Φ of the metal is the minimum amount of energy required to remove an
electron from the surface of the metal.

Question 8

Threshold frequency

Answer 8

Threshold frequency of is minimum frequency of an incident photon that will eject a
photo electron from the surface of the metal.

Question 9

Stopping potential

Answer 9

1）Stopping potential Vs is minimum potential difference
2）between the metal and collector that
will
3)prevent an ejected photo electron from reaching the collector.

Question 10

Characteristic lines

Answer 10

 Electrons in atoms are grouped in various energy states called “shells”. The shell nearest to
the nucleus is known as the K shell, followed by the L shell, M shell and N shell.
 When the fast bombarding electrons knocks out inner shell electrons from the target atoms,
a vacancy is created.
 An electron in the outer shell de-excites to fill the vacancy and emit an X-ray photon. These
X-ray photons have energies that correspond to the energy differences between the energy
levels of the two shells, hence producing X-rays of specific frequencies.

Question 11

relative intensity of the Kα characteristic line is higher than that of the Kβ characteristic line.

Answer 11

Kβ arises when electrons from the M shell fill the vacancy of the K shell
and emit a photon whose wavelength correspond to value of Kβ shell

Kα line arise when electrons from L shell fill in the vacancy in the K shell and in the process emits a photon whose wavelength corresponds to value of the Kα line

The transition when electrons from the M shell fills a vacancy in the K shell has a lower
probability of occurring as compared to the transition when electrons from the L shell fills a
vacancy in the K shell as
2) due to the shielding effects of electrons in the L shell.

Question 12

In the process of X-ray production, metal target is replaced with another metal of higher atomic number, State and explain the effect on maximum energy of X-ray photon present

Answer 12

Remains the same. The values is dependent on accelerating voltage and independent of metal target

Question 13

Produce of continuous spectrum

Answer 13

1)When the bombarding electron collide with the metal atoms in the target, they can lose any
fraction of their initial kinetic energy, up to the maximum in a single interaction.

2) As different amount of their kinetic energies are lost, X-ray photons of VARIOUS WAVELENGTHS are emitted,
resulting in a continuous spectrum represented by the solid line

Question 14

Minimum wavelength of a continuous spectrum

Answer 14

When all of the kinetic energy of a bombarding electron is lost in a single
collision to produce one photon, the most energetic photon with the highest frequency and
lowest wavelength is produced.

Question 15

Emission and absorption line spectra

Answer 15

Emission spectrum: Separate Discrete color lines on dark background

Absorption spectrum: Separate discrete dark lines on a continuous spectrum

Emission Spectrum: Electrons transit from higher to lower energy levels

Absorption spectrum: Electrons transit from lower to higher energy levels

Question 16

Volt

Answer 16

an non-SI unit of energy, equals to the energy gained by an electron when it is accelerated by a potential difference of 1

Question 17

Excited state of an atom

Answer 17

energy of electron which is greater than its minimum in an atom

Question 18

Why energy states in hydrogen atom are negative

Answer 18

The energy of a free electron is maximum and denoted as zero.
Since a bonded electron need to absorb energy to be at lower states, thus their energy states are negative

Question 19

Formation of absorption spectrum

Answer 19

 White light, consisting of photons of a continuous range of frequencies, passes through a
discharge tube containing the gas at low pressure and temperature.

 Photons having the energies that CORRESPOND to the energy difference between two discrete
energy levels are absorbed, causing the electrons are being excited from ground state to
higher energy levels.

o Light of these frequencies appear to be missing from the continuous spectrum,

o The excited atoms then return to their ground state by emitting photons whose energies
are exactly the same as the energy of those photons absorbed in the first place.

o However, only part of this radiation is emitted in the same direction as the incident white
light, so parts of the spectrum corresponding to these frequencies appear dark in
comparison with the intensity of the other frequencies which were not absorbed.

Question 20

Formation of Emission line spectrum

Answer 20

 When a high potential difference is applied across a discharge tube containing the gas at low
pressure, the atoms of the gas are excited through inelastic collisions.

 The excited atoms are highly unstable and will quickly de-excite to lower energy states.

o These excited atoms can, but may not de-excite directly to ground state – it may make
a series of jumps through intermediate energy states to ground state, emitting more than
one photon in the process.

o These photons have energies that correspond to the energy difference between any two
discrete energy levels when the electrons de-excite.

Question 21

Explain why sound waves do not exhibit particle like properties and raindrops do not exhbit wave-like properties

Answer 21

Sound waves undergo diffraction since its wavelength is in the same order of most objects,
Sound waves exhibits wave-like properties

Raindrops do not exhibit diffraction as its wavelength is very small as compared to most objects. Raindrops exhibit particle like properties

Question 22

Why photo electrons emerge with different amount of kinetic energy

Answer 22

Energy of each photon is fixed. Only surface photon emerge with maximum kinetic energy

Question 23

Light has waves and particulate natures

Answer 23

DIFFRACTION AND INTERFERENCE of light—Wave

Photoelectric effect–particle

Question 24

How are X-ray produced

Answer 24

When the cathode is heated by passing a current through it, electrons are produced at the
cathode via thermionic emission with negligible kinetic energies. A high potential difference
is applied between the cathode and anode to accelerate the electrons to the target metal (i.e.
anode) at very high speeds

Electrons lose various energies due to a range of deceleration when collide with target metal. Giving off X-ray photon of different energies .

Question 25

How experimental observations associated with photo electron effect and explain how it deviates from predictions of classical wave theories

Answer 25

1) Quantum: Threshold frequency: Below this frequency, no photo electron emitted regardless of the intensity of electromagnetic radiation
Classical: photo electrons should be emitted at all frequencies

2) Quantum: Maximum is independent of the light INTENSITY, but dependent on the wavelength and frequency of the photons.
Classical: Increase light intensity should increase the KE and speed of photo electrons ejected

3) Quantum: No time lag between illuminating the metal and ejection of photo electrons
Classical: Measurable time lag

Question 26

How plank’s constant h can be determined by using photoelectric effect

Answer 26

1) Reverse the polarity of the battery to obtain stopping potential
2) Vary f to obtain a different value of Vs.
3) Plot Vs against f graph.
4) h equals to the gradient x elementary charge e.

Question 27

Why minimum energy required to liberate electrons from metal surface.

Answer 27

1) Electrons are strongly attracted to positive lattice ions within metals.
2) Minimum work has to be done to overcome the attractions before Electrons could be liberated from metal sirface

Question 28

Increasing photocurrent for values of V between Vs an 0V

Answer 28

1) Electrons are emitted with a range of kinetic energy
2) When the collector is made less negative with respect to emitter, some electrons are able to overcome the electrostatic force of replusion and reach the collector.