Circuit
Wheatstone Bridge: Find an Unknown Resistance from a Null Reading
An ohmmeter measures resistance by pushing a known current through it and reading the voltage — good enough for rough work, but its accuracy...
Biasing
BJT Voltage Divider Bias: A Stable Base Bias That Does Not Drift with Beta
A bipolar transistor only amplifies properly when its base is biased to the right operating point — the Q-point. The trouble is that a trans...
Capacitor
RC High-Pass Filter: Cutoff Frequency and Frequency Response Explained
The RC low-pass filter takes its output across the capacitor and passes the bass. Swap the parts — take the output across the resistor inste...
Efficiency
Transformer Turns Ratio and Efficiency: From 230 V to 12 V, Worked Example
A transformer changes AC voltage without any moving parts: the ratio of the voltages is the ratio of the turns. That one rule sizes everythi...
AC Circuit
Capacitive Reactance: How a Capacitor Behaves in an AC Circuit
A resistor opposes current the same way at every frequency. A capacitor does not: it blocks DC completely, lets high-frequency AC through ea...
Circuit
MOSFET as a Switch: Drive a 12 V Load from a 5 V Logic Signal
A microcontroller pin runs at 5 V and can supply only a few tens of milliamps — it cannot drive a 12 V, 2 A motor directly. The usual answ...
Circuit
Maximum Power Transfer Theorem: Choose the Load That Takes the Most Power
Every real source has some internal resistance — a battery, an amplifier output, or a whole network reduced to its Thévenin equivalent. If...
Capacitor
RC Low-Pass Filter: Cutoff Frequency and Frequency Response Explained
A resistor and a capacitor in series make the most useful filter in electronics: the RC low-pass filter. It passes low frequencies almost un...
Circuit
Voltage Divider: The Formula, the Loading Effect, and How to Design One
Two resistors in series across a supply give you any smaller voltage you want — that is the voltage divider, the simplest circuit in electro...
Circuit
Kirchhoff's Laws: KCL and KVL in a Two-Loop Circuit — Worked Example
Two laws carry almost all of circuit analysis. Kirchhoff's current law (KCL) says that the currents entering a node add up to the curren...
Circuit
LED Series Resistor: How to Calculate the Right Value and Protect Your LED
An LED is a diode that lights up — but it is also a diode, which means it has almost no resistance of its own once it starts conductin...
Circuit
Norton Equivalent Circuit: Replace Any Network with One Current Source and One Resistor
Thevenin's theorem replaces a network with a voltage source and a series resistor. Norton's theorem does the same job the othe...
Circuit
Superposition Theorem: Solve a Two-Source Circuit Step by Step
When a circuit has two or more independent sources, solving it all at once can get messy. The superposition theorem gives a simpler way: con...
Circuit
Inductor Energy and the RL Time Constant: How Current Builds Up in a Coil
A capacitor resists a change in voltage; an inductor resists a change in current. Connect an inductor to a battery through a resistor and th...
Circuit
Thevenin Equivalent Circuit: Replace Any Network with One Source and One Resistor
Faced with a complicated network of sources and resistors, you do not have to analyse the whole thing every time the load changes. Thévenin...
Circuit
Ohm's Law and Resistors in Series and Parallel: Worked Example
Ohm's law — V = I × R — is the first equation of electrical engineering, and the series and parallel rules for resistors are the second....
Capacitor
RC Time Constant: Capacitor Charging and Discharging Explained
Connect a capacitor to a battery through a resistor and it does not charge instantly — the voltage climbs in a smooth exponential curve, fas...
Diode
Half-Wave Rectifier: How One Diode Turns AC into DC
A half-wave rectifier is the simplest AC-to-DC converter there is: one diode and one load resistor. The diode conducts only during the posit...