Resistors Capacitors Safety

What is a resistor?

A passive circuit component used to reduce current flow and voltage levels.

What do the colored bands on a resistor mean?

They signify the amount of resistance and the tolerance.

What does the LAST band on a resistor indicate?

The tolerance.

What does the SECOND-TO-LAST band on a resistor indicate?

The multiplier — what the first bands are multiplied by.

What is a fixed resistor?

A resistor with only one resistance value, which cannot be changed.

Name the three types of fixed resistor.

Carbon composition, wire-wound and metal film.

What is a carbon composition resistor made of?

Carbon graphite and clay.

What is a wire-wound resistor?

A resistor made from wire wound on an insulating form.

What is a metal film resistor?

A metal alloy or carbon film deposited in a vacuum onto a small ceramic cylinder.

What is a variable resistor?

A resistor whose resistance can be set to any value within its range.

Give an everyday example of a variable resistor in use.

Adjusting the volume on a television.

What is a potentiometer?

A resistor with terminals at each end and a movable contact that can be set anywhere along it.

How many terminals does a potentiometer have?

Three — two ends and one adjustable contact.

What are potentiometers commonly used as?

Voltage dividers.

What is a rheostat?

A variable resistor with two terminals, used as a current-limiting device.

How many terminals does a rheostat have?

Two.

What is a rheostat typically used for?

Controlling the light level of incandescent lamps.

Can a potentiometer be wired as a rheostat?

Yes — connect only one end of the resistance element and the movable arm.

How do rheostats and potentiometers compare on power?

Rheostats are often wire-wound and have higher power ratings, typically over 2 W.

What are fuses and circuit breakers?

Safety features that protect a circuit from a power overload.

How do fuses and circuit breakers protect a circuit?

They act as safety switches that break the circuit before large-scale damage is done.

What is a short circuit?

When the current's intended pathway is shorter than it was designed to be.

Why is a short circuit dangerous?

It causes a surge in current through the circuit.

What is a capacitor?

A passive component that temporarily stores electrical energy in a circuit.

How is a capacitor built?

Two conducting plates separated by a distance, with a dielectric between them.

What is a dielectric?

A material that can become polarized, placed between a capacitor's plates.

How does a capacitor act like a battery?

Once charged, the voltage source can be removed and the capacitor can discharge to provide energy.

What is the capacitance formula?

C = Q / V, where C is capacitance, Q is charge and V is voltage.

What unit measures capacitance?

Farads.

What is capacitive reactance?

The impedance a capacitor has in response to the frequency of an AC circuit.

What is the capacitive reactance formula?

Xc = 1 / (ω C), where ω is angular frequency and C is capacitance.

Name the three passive circuit components.

Resistors, capacitors and inductors.