3 Current and Circuits Free Online FlashCards

What does electric current measure?

Electric current is the rate at which charge passes a conductor’s cross-section: $I=\frac{\Delta Q}{\Delta t}$. One ampere equals one coulomb per second.

How does conventional current compare with electron drift in a metal wire?

Conventional current points in the direction positive charge would move, from a source’s positive terminal toward its negative terminal. Electrons in metal wires drift in the opposite direction.

What characterizes steady-state direct current?

Direct current (DC) flows in one direction. In a steady-state DC circuit, its magnitude is constant.

State Ohm’s law for an ohmic resistor.

For an ohmic resistor, Ohm’s law is $V=IR$, where voltage is measured in volts, current in amperes, and resistance in ohms.

How do a uniform wire’s length and thickness affect its resistance?

For a uniform wire, $R=\rho\frac{L}{A}$. Greater length increases resistance; greater cross-sectional area decreases it.

What formulas give the power converted by a resistor?

A resistor’s electrical power can be written as $P=IV=I^2R=\frac{V^2}{R}$.

What does a source’s electromotive force represent?

A source’s electromotive force (emf) is the energy it supplies per unit charge, measured in volts. Despite its name, emf is not a force.

How does internal resistance affect a source’s terminal voltage under load?

For a source with internal resistance $r$ supplying current $I$, terminal voltage is $V_{\text{terminal}}=\varepsilon-Ir$. It is below the emf while current flows.

What are the current and equivalent-resistance rules for series components?

In series, the same current flows through every component, and the equivalent resistance is $R_{\text{eq}}=R_1+R_2+\cdots$.

What are the voltage and equivalent-resistance rules for parallel components?

Parallel components share the same voltage across their branches, and branch currents add. Their equivalent resistance satisfies $\frac{1}{R_{\text{eq}}}=\frac{1}{R_1}+\frac{1}{R_2}+\cdots$.

What does Kirchhoff’s junction rule state?

The junction rule states that total current entering a junction equals total current leaving it, expressing conservation of charge.

What does Kirchhoff’s loop rule state?

The loop rule states that the algebraic sum of voltage changes around any closed loop is zero, expressing conservation of energy.