Chapter 16: Basic Electronics

Definition: The process of emission of electrons from the surface of hot metal is called thermionic emission.

Cathode Rays: Electrons emitted from the hot surface of cathode. Discovered by J.J. Thomson (1897). Deflected by electric and magnetic fields, showing they are negatively charged.

Device: An instrument used to display the magnitudes of rapidly changing electric currents or potentials.

Components:

• Electron Gun: Produces a beam of fast-moving electrons (Thermionic emission). Includes Filament, Cathode, Grid (Brightness control), and Anodes (Focusing/Accelerating).
• Deflecting Plates: X-plates (Horizontal deflection) and Y-plates (Vertical deflection).
• Fluorescent Screen: Coated with phosphor, glows when struck by electrons.

Uses: Displaying waveforms, measuring voltages, echo-sounding, displaying heartbeats.

Analogue Quantities: Quantities that change continuously with time (e.g., Temperature, Time, Sound). Processed by Analogue Electronics.

Digital Quantities: Quantities that change in discrete steps (0 and 1). Processed by Digital Electronics.

Converters:

• ADC (Analogue to Digital Converter): Converts analogue signals to digital (binary).
• DAC (Digital to Analogue Converter): Converts digital output back to analogue form (e.g., for speakers).

Boolean Algebra: Algebra of logic with two states: 0 (Low) and 1 (High).

• AND Gate: Output is 1 only if all inputs are 1. ($X = A \cdot B$). Symbol: Series switches.
• OR Gate: Output is 1 if at least one input is 1. ($X = A + B$). Symbol: Parallel switches.
• NOT Gate: Inverter. Output is opposite of input. ($X = \bar{A}$).
• NAND Gate: AND + NOT. Output is 0 only if all inputs are 1. ($X = \overline{A \cdot B}$).
• NOR Gate: OR + NOT. Output is 1 only if all inputs are 0. ($X = \overline{A + B}$).

Uses: Safety Alarms (Burglar alarm using NAND gate and LDR).