The algebraic sum of currents at a node equals zero, so $$\sum I_{\text{in}} = \sum I_{\text{out}}$$

The voltage around any closed loop is proportional to resistance

Power equals voltage times current, $$P=VI$$

Current in a series circuit is divided among branches

The sum of voltage rises and drops around any closed loop equals zero

The total current entering a node equals the total leaving the node

Voltage is proportional to current by $$R$$

Power dissipated equals $$I^2R$$

It melts to permanently open a circuit when current exceeds a rating

It mechanically trips to open the circuit when overcurrent or short‑circuit conditions occur and can be reset

It stores energy and releases it back into the circuit

It steps voltage up or down using magnetic coupling

To regulate voltage

To open the circuit by melting when current exceeds a rated value, protecting components

To measure current

To store charge

Set to voltage range and connect probes in parallel across the component or source

Set to current range and place the meter in series with the circuit

Set to resistance range and disconnect power

Short the leads together before connecting across the source

Set to current range, move the lead to the correct current jack, and place the meter in series with the circuit

Set to voltage range and connect in parallel

Set to resistance range and measure across a powered circuit

Connect the meter across the supply to read line current

Set to resistance range, remove power from the circuit, and measure across the component

Set to voltage range and connect across the powered circuit

Set to current range and place the meter in series under power

Short the component and read the display

A resistor placed to simulate or provide a specified load, drawing current to test or stabilize operation

A resistor used only for measuring resistance in ohmmeters

A device that steps up voltage for heavy loads

A short circuit used during troubleshooting

Components are connected end‑to‑end so the same current flows through each

Components share the same two nodes so each branch has the same voltage across it

Voltage adds across components while current stays the same in all branches

There is only one component in the circuit

$$P=VI$$

$$V=IR$$

$$I=\dfrac{V}{P}$$

$$R=\dfrac{P}{I}$$

They indicate wire gauge; read from center outward

They indicate resistance value and tolerance; read from the end with closely spaced bands using digit, multiplier, and tolerance bands

They indicate resistor wattage only; read from the widest band first

They indicate the manufacturing date; read left to right only

Ohms measure resistance; Watts measure power dissipation

Ohms measure power; Watts measure resistance

Ohms measure current; Watts measure voltage

Ohms and Watts both measure resistance

$$V=IR$$

$$P=VI$$

$$I=PR$$

$$R=\dfrac{P}{V}$$

Very high current and a blown fuse

No current flow with full supply voltage present across the open component or path

Low resistance reading across a conductor

Equal currents in parallel branches

No current flow and a large voltage drop across a break

Excessive current with near‑zero resistance between points that should be isolated

Normal current and normal voltage across a load

Increased resistance due to heat

To interrupt overcurrent and prevent damage and fire hazards

To increase circuit voltage for higher power

To store excess electrical energy for later use

To convert AC to DC for safer operation

A series circuit has a single path for current; a parallel circuit has multiple paths

A series circuit uses only resistors; a parallel circuit uses only capacitors

A series circuit provides equal voltage to all components; a parallel circuit provides equal current

A series circuit always consumes more power than a parallel circuit

Voltage

Current

Resistance

Power

Total current increases

Total current decreases

Total current stays the same

Total current oscillates

Use the reciprocal sum: $$1/R_T = \sum (1/R_i)$$

Add all resistances directly: $$R_T = \sum R_i$$

Multiply all resistances: $$R_T = \prod R_i$$

Subtract the smallest resistance from the largest

Approximately $$54.5\,\Omega$$

$$33.3\,\Omega$$

$$100\,\Omega$$

$$600\,\Omega$$

The other branches continue to carry their currents; only total current decreases

All current stops in the entire circuit

Current doubles in the remaining branches

Voltage across the source drops to zero

$$I_1 = I_T\,\dfrac{R_2}{R_1+R_2}$$

$$I_1 = I_T\,\dfrac{R_1}{R_1+R_2}$$

$$I_1 = I_T\,\dfrac{R_T}{R_2}$$

$$I_1 = \dfrac{V}{R_1+R_2}$$

$$0.12\,\text{A}$$

$$1.2\,\text{A}$$

$$0.012\,\text{A}$$

$$0.83\,\text{A}$$

Approximately $$0.65\,\text{W}$$

Approximately $$1.8\,\text{W}$$

Approximately $$2.2\,\text{W}$$

Approximately $$0.12\,\text{W}$$

Measure equal voltage across each branch and verify that the sum of branch currents equals the source current

Measure different voltages across each branch and ensure they add to the source voltage

Measure resistance across a powered circuit to confirm equal currents

Use the diode test mode to confirm each branch has the same resistance

Current

Voltage

Resistance

Power

Add all resistances: $$R_T = \sum R_i$$

Use the reciprocal sum: $$1/R_T = \sum (1/R_i)$$

Multiply all resistances: $$R_T = \prod R_i$$

Average all resistances: $$R_T = \overline{R}$$

Current decreases

Current increases

Current remains unchanged

Current alternates direction

$$600\,\Omega$$

$$100\,\Omega$$

$$300\,\Omega$$

$$33.3\,\Omega$$

$$12\,\text{V}$$

$$7\,\text{V}$$

$$10\,\text{V}$$

$$2\,\text{V}$$

The entire circuit opens and current stops

Only the voltage across the open resistor increases slightly

Current diverts to other branches

Total resistance decreases and current rises

$$V_1 = V_S\,\dfrac{R_1}{R_1+R_2}$$

$$V_1 = V_S\,\dfrac{R_2}{R_1+R_2}$$

$$V_1 = I\,(R_1+R_2)$$

$$V_1 = \dfrac{V_S}{R_1\,R_2}$$

$$12\,\text{V}$$ each

$$6\,\text{V}$$ each

$$24\,\text{V}$$ each

$$0\,\text{V}$$ each

Open the circuit and place the meter in series using the ammeter function

Place the meter across the supply on the voltage range

Measure resistance of the whole circuit while powered

Use the capacitance range across one resistor

In series, components share the source voltage proportionally to resistance; in parallel, each branch has full source voltage and power depends on its branch current

In series, each component receives full source voltage; in parallel, voltage is split among branches

In series, total power equals the smallest component’s power; in parallel, total power equals the largest component’s power

In series and parallel circuits, power is always identical for every component regardless of resistance