Electrical and Electronics Foundations for Mechanical Engineers

Electric charge

A property of matter that causes electrical forces.

Current

The rate at which charge flows, represented by the formula I = dQ/dt.

Voltage

Electric potential difference that drives current, defined as V = W/Q.

Resistance

Describes how strongly a component opposes current flow, represented by R = V/I.

Electrical power

The rate of energy transfer, calculated using P = VI.

DC (direct current)

Voltage and current are ideally constant with time.

AC (alternating current)

Voltage and current vary with time, often sinusoidally.

Electrical safety

Precautions taken to prevent electrical hazards, including isolation and grounding.

Digital multimeter (DMM)

A tool for measuring voltage, current, resistance, and sometimes other parameters.

Ohm's Law

The relationship V = IR for ohmic elements, relating voltage, current, and resistance.

Tolerance

The allowable variation from a nominal resistance in a resistor.

Power rating

The maximum power a resistor can dissipate without damage.

Conductance (G)

The reciprocal of resistance; G = 1/R.

Kirchhoff’s Current Law (KCL)

The algebraic sum of currents entering a node equals zero.

Kirchhoff’s Voltage Law (KVL)

The algebraic sum of voltage rises and drops around a closed loop equals zero.

Voltage divider

A circuit that produces a fraction of the input voltage using two resistors.

Current divider

A formula used to find the current through parallel resistors.

Nodal analysis

A systematic method to analyze circuits using KCL at nodes.

Thévenin equivalent

A simplified circuit model consisting of a voltage source and resistance.

Norton equivalent

A simplified circuit model involving a current source in parallel with resistance.

Capacitance (C)

A measure of a capacitor's ability to store charge, related to i(t) = C dv(t)/dt.

Inductance (L)

A property of an inductor that stores energy in a magnetic field, defined by v(t) = L di(t)/dt.

Time constant (τ)

For RC circuits, τ = RC; for RL circuits, τ = L/R.

Root Mean Square (RMS)

The effective value of an AC signal used for power calculations.

Rectification

The process of converting AC to DC using diodes.

DIODE

A semiconductor device that allows current to flow in one direction.

PWM (Pulse Width Modulation)

A technique for controlling power by varying the duty cycle.

Flyback diode

A diode used to protect circuits from voltage spikes when inductive loads are turned off.

Operational Amplifier (op-amp)

A high-gain differential amplifier used for signal conditioning.

Negative feedback (in op-amps)

A feedback mechanism that stabilizes and controls the output voltage.

Resistive sensors

Sensors that output a resistance change proportional to the measured quantity.

Analog-to-Digital Converter (ADC)

A device that converts continuous signals into discrete digital numbers.

Signal ground

The reference voltage level against which other signals are measured.

Power return

The conductor that carries load current back to the power source.

Star grounding

A grounding technique to minimize ground loops and signal interference.

Shielding

Using conductive materials to protect signals from electromagnetic interference.

Voltage drop in wiring

The reduction in voltage in electrical circuits due to resistance over distance.

Sensor conditioning

The process of amplifying, filtering, and preparing sensor signals for processing.

Mechanical switch bounce

Rapid make/break of contacts in mechanical switches when closed.

Noise margin

The amount of voltage disturbance a digital signal can tolerate without being misinterpreted.

Pull-up resistor

A resistor connected between an input and a high voltage to prevent floating inputs.

Back-emf

Voltage generated in an inductor or motor acting against the applied voltage.

RMS calculation for AC

For a sinusoid, Vrms = Vp/√2.

Interaction of AC and DC

Devices often see both AC components (like ripple) and DC power.

Strain gauge

A type of sensor that measures deformation through resistance change.

Common-Mode Rejection Ratio (CMRR)

The ability of a differential amplifier to reject common signals.