SAAT Physics 4 Section 4-6 (Quantum Theory, The Atom, Solid-State Electronics) - تحصيلي

Objects glow when

They reach a high temperature

Electromagnetic radiation

Depends on the temperature and other properties of an object, typically consists of a continuous distribution of wavelengths from the infraref, visible, and ultraviolet portions of the spectrum

The distribution of the intensity of the different wavelengths

Varies with temperature

Blackbody radiation

The radiation emitted by a blackbody, which is a perfect radiator and absorber and emits radiation based only on its temperature

The intensity of blackbody radiation at three different temperatures

Classical theory’s prediction for blackbody radiation (blue curve) did not correspond to the experimental data (red data points) at all wavelengths

Planck’s theory is the only one that corresponds with the data

Total energy of a resonator with frequency formula

En = nhf

The photoelectric effect

When light strikes a metal surface, the surface may emit electrons

Photoelectrons

Refer to the electrons that are emitted in the photoelectric effect

Photosensitive

Refer to those surfaces that exhibit the photoelectric effect

According to classical physics,

Light waves of any frequency should have sufficient energy to eject electrons from the metal if the intensity of the light is high enough

At lower intensities,

Electrons should be ejected if light shines on the metal for a sufficient time period

Electrons would take time to

Absorb the incoming energy before acquiring enough kinetic energy to escape from the metal

Increasing the intensity of the light waves should

Increase the kinetic energy of the photoelectrons, and the maximum kinetic energy of any electron should be determined by the light’s intensity

Threshold frequency

The minimum frequency of electromagnetic radiation (such as light) required to eject electrons from a metal surface (differs from metal to metal)

If the light frequency exceeds the threshold frequency,

The photoelectric effect is observed

The number of photoelectrons emitted is proportional to

The light intensity; but the maximum kinetic energy of the photoelectrons is independent of the light intensity

Planck’s formula

E = hf

The work function is equal to hft

ft is the threshold frequency for metal

Photons with energy greater than hft eject

Electrons from the surface of and from within the kinetic energy

Maximum kinetic energy of a photoelectron

KE = hf - hf_1

Arthur Compton

Found that, if light behaves like a particle, then a collision between an electron and a photon should be similar to a collision between two billiard balls

The amount that the wavelength shifts depends on

The angle through which the proton is scattered

Compton shift is difficult to detect using visible light, but

It can be observed using electromagnetic waves with much shorter wavelengths (like X-rays)

Matter waves

The wave-like behaviors exhibited by particles of matter (such as electrons, protons, and atoms) as part of wave–particle duality in quantum mechanics

Wavelength of matter waves

$\lambda$ = h/p

The uncertainty principle

It is fundamentally impossible to measure both the precise position and momentum (velocity) of a quantum particle (like an electron) simultaneously

An electron's location is described by a probability distribution

Simultaneous measurements of position and momentum cannot be completely certain.

Rutherford's model of the atom

Describes the atom as a miniature solar system with a tiny, dense, positively charged nucleus at the center containing most of the mass, surrounded by negatively charged electrons orbiting it

Region of the atom as a nucleus

The positive charge and most of the mass of an atom is concentrated in an extremely small volume

Orbits

Electrons surrounding the nucleus revolve around it with very high speed in circular paths.

Electrons being negatively charged and nucleus being a densely concentrated mass of positively charged particles are held together by

A strong electrostatic force of attraction

Bohr model of an atom

A hydrogen atom (Z = 1) or a hydrogen-like ion (Z > 1), where the negatively charged electron confined to an atomic shell encircles a small, positively charged atomic nucleus and where an electron jumps between orbits, is accompanied by an emitted or absorbed amount of electromagnetic energy (hν)

Hydrogen emission spectrum

When electrons in an atom or a molecule absorb energy and get excited, they jump from a lower energy level to a higher energy level, and they emit radiation when they retur to their onginal states

Importance of the hydrogen spectrum

It’s evidence showing that the atom’s electronic structure is quantized

Absorption and emission

The electron absorbs the energy and jumps to a higher energy level; in the reverse process, emission, the electron returns in the ground sale by releasing the extra energy it absorbed

When the light from an atomic gas is passed through a prism or a diffraction grating,

The dispersed light appears as a series of distinct, bright spectral lines

The Balmer series

The part of the hydrogen emission spectrum which is responsible for the excitation of an electron to the second shell from any other higher shell

Laymen series - ultra violet light

The transition to the first shell from any other higher shell

Balmer series - visible light

The transition to the second shell from any other higher shell

Paschen series - infrared rays

The transition to the third shell from any other higher shell

Bracket series

The transition to the fourth shell from any other higher shell

Pfund series

The transition to the fifth shell from any other higher shell

Laser

A device that stimulates atoms or molecules to emit light at particular wavelengths and amplifies the light (typically producing a very narrow beam of radiation)

Acronym of laser

Light amplification by the stimulated emission of radiation

Lasers in medicine

Eye surgeries

Lasers in industries

Cutting and wielding metals, checking metal bars, checking and measuring tunnels and tubes

Lasers in science and technology

Measuring movement of the tectonic plates, and in scientific experiments

Band theory of solids

A theoretical model explaining the states of electrons, in solid materials, that can have values of energy only within certain specific ranges

In atoms, electrons are filled with respective energy orbits following Pauli’s exclusion principle

Two atomic orbitals combine to form a molecular orbit with two distinct energy levels

Pauli’s exlusion principle

No two identical fermions (such as electrons) in an atom or molecule can occupy the same quantum state simultaneously

Energy band in solids

Having many energy bands including valence band, conduction band, forbidden band

Valence band

Energy band that consists of valence electrons energy levels (presemt below the conduction band and the electrons of this band are loosely bound to the nucleus of the atom)

Conduction band

Energy band that consists of free electrons energy levels

(for electrons to be free, external energy must be applied such that the valence electrons get pushed to the conduction band and become free)

Forbidden band (also known as the forbidden gap)

The energy gap between the valence band and the conduction band

The electrical conductivity of a solid is determined by the

Forbidden gap and the classification of the materials such as conductors, semiconductors, and insulators

The difference between the valence band and the conduction band

The band gap or energy gap

In semiconductors, current conduction by holes is as important as

Electron conduction; important to become familiar in thinking of the holes as mobile particles carrying positive charges and negative charges

Diodes

Used to protect circuits by limiting the voltage and to also transform AC into DC

Semiconductors

Like silicon and germanium are used to make the most of the diodes

Even though most semiconductors transmit currents in a single direction,

The way which they transmit differs

Detailed definiton of a diode

A two-way terminal electronic component that conducts electricity primarily in one direction

Diodes have high resistance on one end and

Low resistance on the other end

P-type semiconductors

An intrinic semiconductor doped with boron or indium

The majority of carries in p-type semiconductors

Are holes

Electrons are minority carriers

In p-type semiconductors

In a p-type semiconductor, the hole density is

Much greater than the electron density

The acceptor energy level of the p-type is close to the

Valency bond and away from the conduction brand

N-type semiconductors

An instrinsic semiconductor doped with phosphorus or antimony as impurity

The majority of charge carriers in the n-type electrons

Are electrons

Forward-biased diode

When there’s a small drop of voltage across the diode and the current is conducting

Reverse-biased diode

When the battery’s voltage is dropped completely

Zero-based diode

The voltage potential across the diode is zero

Transistor

A type of a semiconductor device that can be used to both conduct and insulate electric current or voltage

P-N-P transistor

Where one n-type material is introduced or placed between two p-type materials

N-P-N transistor

When one p-type material is present between two n-type materials

PNP transistor image

NPN transistor image