Circuits and Power

What is needed to form a circuit?

A voltage source, such as a battery, with conducting materials connecting both terminals.

Why does a circuit need a load?

Without one the circuit would just heat the wires. A load lets the current do work.

What is a load?

Any component that drains power from a circuit.

Give three examples of a load.

Light bulbs, refrigerators and computers.

Do loads generate power?

No. They only dissipate power from the circuit.

What is a closed circuit?

One where all components are connected by conducting wires to each other and a voltage source.

What is an open circuit?

One where a connection is broken, so it will not function.

Which circuit works, closed or open?

A closed circuit works. An open circuit cannot.

What is a series circuit?

One where all components are connected one after the other, with only a single path for the current.

What is the same everywhere in a series circuit?

The current — the same current runs through every component.

How do you find total resistance in a series circuit?

Add the resistances together.

How do you find total voltage in a series circuit?

Add the voltage drops across each component.

What is equivalent resistance?

The total resistance of a circuit, written Req. It is what you use in Ohm's law calculations.

What is a parallel circuit?

One with more than one path for current to pass through.

What is the same across every branch in a parallel circuit?

The voltage drop.

What varies between branches in a parallel circuit?

The current, if the components on those paths differ.

What is the equivalent resistance formula for a parallel circuit?

1/Req = 1/R1 + 1/R2 + …

What happens if one branch of a parallel circuit is disconnected?

Current keeps flowing through the remaining branches.

What happens if a series circuit is broken at any point?

The whole circuit stops — there is only one path.

What is a series-parallel circuit?

A combination of parallel resistor groups connected in series with other resistors or groups.

How do you analyze a series-parallel circuit?

Resolve each series group and each parallel group into its equivalent resistance, repeating as many times as needed.

What is electrical power?

A measure of how much work a circuit can do per unit of time.

What are the three electrical power formulas?

P = V × I, P = R × I², and P = V² / R.

In a circuit, what generates power and what dissipates it?

The voltage source generates it; the loads dissipate it.