Electrical Measurements and Network Theorems Practice Flashcards

Flashcards covering electrical safety, instrument measurements, network theorems (Thevenin, Norton, Superposition, Millman), and AC resonance concepts.

Conservative Body Resistance Figure

The value considered for safety calculations when dry skin ($1,000,000\,\Omega$) is wet or damaged, defined as $1,500\,\Omega$.

Current Interruption Devices

Processes or components used for safety including fuses, automatic circuit breakers, and heat coils.

Moving Iron Instrument AC Reading

The reading obtained when a device with $R=500\,\Omega$ and $L=1\,H$ is fed by $250\,V, 50\,Hz$ AC, calculated as $248\,V$.

Shunt Resistance ($R_{sh}$)

The resistance required to convert a moving coil instrument into an ammeter; for a $0.6\,\Omega$ meter with $0.1\,A$ full scale to reach $15\,A$, it is $0.004\,\Omega$.

Potentiometer Accuracy Advantage

It is more accurate than a voltmeter for DC voltage measurement because it does not load the circuit at all.

Voltmeter Resistance ($R_v$)

Calculated by multiplying the sensitivity ($\Omega/V$ rating) by the full-scale voltage ($V_{fs}$); at $10\,k\Omega/V$ on a $25-V$ range, it is $250\,k\Omega$.

Ammeter and Voltmeter Exchange

Exchanging the position of these instruments in a circuit may result in damage to the ammeter due to its low internal resistance.

Ohmmeter Capacitor Test (All Right)

An indication of low resistance initially that finally moves to the infinity position when connected to a capacitor.

Mesh Analysis Condition

The circuit must be planar, meaning there are no crossing conductors without connections.

Maximum Power Transfer Theorem Efficiency

The efficiency when the load resistance matches the Thevenin equivalent resistance ($R_{th} = R_L$) is $50\%$.

Thevenin's Voltage ($V_{th}$) Definition

Defined as the open-circuit voltage ($V_{ab}$) across two output terminals.

Superposition Theorem Requirement

Requires linearity in the circuit, failing if components like resistors change resistance with temperature.

Reciprocity Theorem

States that if a voltage source $V$ in branch A produces a current $I$ in branch B, moving the source $V$ to branch B will produce current $I$ in branch A.

Millman's Theorem

The most efficient theorem for finding the voltage at a single node where branches containing voltage sources and series resistors meet in parallel.

Compensation Theorem Polarity

If a branch resistance changes by $\Delta R$, the ideal compensating voltage source is $V_c = I\Delta R$ with a polarity that opposes the original branch current $I$.

Independent Mesh Equations

The number of equations required to solve a planar circuit with $n$ nodes and $b$ branches, given by $b - n + 1$.

Supernode Current Determination

The current through an ideal voltage source in a supernode is found by applying KCL at either node individually and summing currents from connected branches.

Parallel Resistor Addition

The total resistance of a network decreases when an additional resistor is added in parallel.

Series-Parallel Resistor Matrix (3x3)

A configuration where the net resistance of nine identical resistors equals the value of a single resistor.

Temperature Coefficient of Resistance ($\alpha$)

A factor used to determine steady temperature based on resistance change, such as in heater wire where $R_1=65\,\Omega$ and $R_2 \approx 78.57\,\Omega$ results in $T_2 = 1255^\circ C$.

Steady-State Capacitor Behavior ($t=0$)

Behaves as a short circuit immediately after a switch is closed because the voltage across it cannot change instantaneously.

Full Transition (RL Circuit)

The transient part reaches more than $99\%$ of its final value after $5$ time constants ($5\tau$).

RC Discharge Rate

If the resistance is doubled while capacitance is constant, the capacitor discharges more slowly because the time constant $\tau = RC$ increases.

Series RLC Resonance Power Factor

The power factor ($pf = \cos(\theta)$) is exactly $1$ (unity) because the circuit is purely resistive.

Parallel RLC Resonance Characteristics

The line current is at its minimum and overall impedance ($Z$) is at its maximum.

Flywheel Effect

The phenomenon in a resonant LC (tank) circuit where energy oscillates between the capacitor and the inductor.

Inductive State (Parallel Resonant Circuit)

A state occurring at frequencies below the resonant frequency ($f < f_r$).

Resonant Phase Relationship

The total source voltage and total line current are in phase.

Power Factor

The ratio of true power (measured in Watts) to apparent power (measured in VA).