ELNG 154: Basic Electronics - Nature of Atoms and Vacuum Valves

This flashcard set covers the nature of atoms, atomic structure, thermionic emission, and the characteristics and parameters of vacuum valves such as diodes, triodes, tetrodes, and pentodes.

Atom

A particle of matter that uniquely defines a chemical element, consisting of a central nucleus surrounded by one or more negatively charged electrons.

Nucleus

The positively charged center of an atom containing relatively heavy particles known as protons and neutrons.

Valence shell

The outermost shell or orbital of an atom where electrons take part in bonding with other atoms.

Magnesium ($Mg$)

An element with an atomic number of $12$ and $2$ electrons in its valence shell.

Semiconductor

An atom that behaves as such if it has $4$ valence electrons, acting as an insulator at low temperatures and a conductor at higher temperatures.

Conductor

An atom that behaves as such if the number of valence electrons is less than $4$, allowing conduction even at room temperature.

Insulator

An atom that behaves as such if the number of valence electrons is greater than $4$, requiring a huge amount of energy to lose an electron.

Band Gap (Conductors)

A state where the valence band overlaps with the conduction band, allowing valence electrons to move essentially free into the conduction band.

Band Gap (Insulators)

A large "forbidden" gap in energies that prevents electrons from jumping from the valence band into the conduction band.

Thermionic emission (Edison Effect)

The release of electrons from a heated material when thermal energy overcomes the material’s work function, first observed by Thomas Edison in $1883$.

Work function

The minimum energy needed to remove an electron from the surface of a solid.

Secondary emission

Emission that occurs when high-velocity electrons strike a conductor in a vacuum, knocking out one or more electrons from the surface.

Photo emissions

Emission that occurs when energy in the form of light falls upon the surface of a conductor, knocking out electrons.

Colossus

Regarded as the world’s first programmable, electronic, digital computer ($1943–1945$) which used thermionic valves to perform Boolean and counting operations.

Thermionic diode

A vacuum chamber device using a low D.C. voltage ($6V$) to heat a tungsten filament and a high voltage ($400V$) to accelerate electrons from a cathode to an anode.

Triode

The first electronic amplification device, consisting of three active electrodes: the filament or cathode, the grid, and the plate or anode.

Grid bias

The value of grid voltage which makes it positive or negative in relation to the cathode to control anode current.

Amplification Factor ($\mu$)

The ratio of change between plate voltage and grid voltage, denoted as $\mu = \frac{\Delta V_p}{\Delta V_G}$, provided plate current remains constant.

Plate Resistance ($r_p$)

The internal resistance of a tube defined as the ratio of change in plate voltage to the ratio of change in plate current, mathematically $R_p = \frac{\Delta V_p}{\Delta I_p}$.

Transconductance ($g_m$)

Also called mutual conductance, it is the ratio of a change in plate current relative to change in grid voltage ($g_m = \frac{\Delta I_p}{\Delta V_0}$) while plate voltage is constant.

Tetrode

A multi-electrode valve consisting of $4$ electrodes: anode, cathode, control grid ($G1$), and screen grid ($G2$).

Screen grid

An additional grid in a tetrode that acts as a veil between the control grid and the anode to create an effective electrostatic field.

Pentode

A multi-electrode valve consisting of $3$ grids and $5$ electrodes total.

Multi-electrode valves (m.e.v)

Tubes with more than three electrodes, including the hexode ($6$ electrodes), heptode ($7$ electrodes), and octode ($8$ electrodes).