Topic
Electricity & Magnetism
From charge and field geometry through potential, circuits, magnetic forces and induction, with derivations and energy checks.
Start Here
- Electric Fields: Charge, Superposition, and CancellationWhy can a neutral object respond to electricity, and why does zero total charge not imply zero field? The answer requires separating sources, fields, and the charge experiencing a force.
Go Deeper
- Electric Flux and Gauss’s Law: When Symmetry Does the WorkGauss's law is always true for electric fields, but it is not always a shortcut for finding them. Its power comes from combining a global accounting rule with enough symmetry to determine a local field.
- Electric Potential: Turning a Field into an Energy LandscapeVoltage is not a stock of charge or a force. It is potential-energy difference per unit charge. This lets us translate the local force description into the energy accounting already familiar from mechanics.
- Current, Resistance, and Power: Where Electrical Energy GoesClosing a circuit does not send a fresh batch of electrons from a battery to a distant lamp at light speed. Mobile charges are already present in the wires. Changes in electromagnetic fields propagate through the circuit, establishing a drift motion whose speed is usually much smaller than the signal speed.
- DC Circuits: Kirchhoff’s Laws and Loaded SourcesA circuit drawing is a claim about connections, not a picture of physical wire positions. Two components are in parallel only if both ends connect to the same two nodes. They are in series only when the same current must pass through both, with no branching junction between them.
- Capacitors and RC Circuits: Energy Storage Takes TimeA capacitor stores energy by separating opposite charges, creating an electric field between conductors. In the ideal two-terminal model the plates hold +Q and -Q; the device can remain neutral overall while storing energy.
- Magnetic Fields and Forces: Bending Motion Without Doing WorkElectric fields can push a stationary charge. Magnetic force on a point charge depends on its motion. The combined classical Lorentz force is
- Electromagnetic Induction: Flux Change, Lenz’s Law, and EnergyA stationary magnet near a stationary wire does not continually generate current. What matters is a change in magnetic flux through a circuit, or motion that produces the equivalent electromechanical effect.