Electrical Systems

DC Circuit Components 221

DC Circuit Components provides a comprehensive overview of the different parts that appear in DC circuits, including source, path, control, and load. DC power sources include batteries, generators, and piezoelectricity. The path of a circuit is made of a conductor, which has low resistance, but other materials with more resistance, such as insulators, semiconductors, and resistors, are often also used in circuits. In general, switches are used to control current, but many circuits also have safety devices, such as fuses and breakers, to protect the circuit from high current conditions.

Understanding the purpose of different components is essential for working with DC circuits. After taking this class, users should have a firm grasp of many different circuit components and understand when and why they are used. This knowledge will allow them to design effective circuits and recognize potential problems with a circuit’s components.

  • Difficulty Intermediate

  • Format Online

  • Number of Lessons 16

  • Language English


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Course Outline
  • Circuit Components
  • Batteries
  • Battery Chemistry
  • Types of Batteries
  • Generators
  • Piezoelectricity
  • DC Power Sources Review
  • Conductors
  • Insulators
  • Semiconductors
  • Resistors
  • Conductivity and Resistance Review
  • Switches
  • Fuses
  • Circuit Breakers
  • Control Components Review
  • Identify the basic components of a DC circuit.
  • Describe the electromotive series.
  • Describe batteries.
  • Distinguish between primary cell and secondary cell batteries.
  • Describe how generators work.
  • Describe piezoelectricity.
  • Describe conductors.
  • Describe insulators.
  • Describe semiconductors.
  • Describe resistors.
  • Describe how common switches work.
  • Describe how fuses work.
  • Describe how circuit breakers work.
Vocabulary Term


A corrosive substance with a sour flavor. Acid mixtures are conductive electrolytes.


A substance that is notable for its low number of hydrogen ions. Alkaline mixtures are conductive electrolytes.


A highly conductive, lightweight, silvery metal. Aluminum is often used in long-distance power distribution.


The part of a generator in which current is induced. Armatures usually rotate between two pole pieces.


A metallic element used as an impurity in a doped semiconductor. Arsenic increases the number of electrons in the valence shells of the semiconductor's atoms.


A device that converts chemical energy into electrical energy. Batteries are a source of direct current.

bimetallic strip

A component made of two metals with different expansion temperatures so that it curls up when exposed to heat. Bimetallic strips are often used to detect temperature in circuit breakers.

building codes

Local standards dictating rules for building safety. Building codes may not allow aluminum wire to be used for residential structures.

button-cell battery

A small, button-like battery that provides power for watches and very small devices. Button-cell batteries are primary cell batteries.


A common non-metallic element that is very strong and resistant to heat. Carbon is used to form the body of resistors.


A single unit of a battery. A cell contains two different metals in an electrolyte solution.

chemical reaction

A process in which one or more substances are changed into another substance or substances. Chemical reactions allow batteries to produce electricity.

circuit breaker

An overcurrent device with a bimetallic strip that bends and trips a switch to open a circuit. Circuit breakers detect excess current to prevent overheating in a circuit.


A material or element that allows free movement of electrons and therefore allows easy flow of electricity. Conductors are typically metals.


Connecting points between two conductors that allow electricity to flow when they are closed. Contacts prevent the flow of electricity when open.


A component in a circuit that regulates the flow of electricity. The control determines when a circuit is energized.


A highly conductive, reddish-brown metal. Copper is often used as an electrical conductor in houses, buildings, and machinery.


Direct current. Electricity that travels in one direction. DC does not reverse the direction of flow.


An electronic device with two terminals that allows electric current to flow in only one direction. Diodes use polarity to control current flow.

direct current

DC. Electricity that travels in one direction. Direct current does not reverse the direction of flow.

doped semiconductor

A semiconductor that has an added impurity. Doped semiconductors contain impurities to increase conductivity.

dry-cell battery

A device containing a paste electrolyte that converts chemical energy into electrical energy. Dry-cell batteries include button-cell batteries.

electric shock

The flow of electricity through the body. Electric shock can be fatal.


A device within a circuit that conducts electricity. Electrodes have a positive or negative charge.


A conductive solution containing an acid, an alkaline, or a salt. The electrolyte in a battery connects the two electrodes.

electromotive series

A list of metals in order of most reactive, or most likely to give up electrons, to least reactive. The electromotive series lists metals that are used in batteries.

fixed resistor

A device that resists only a specific amount of current flow. A fixed resistor consists of a carbon body with metallic leads.


An overcurrent device with a metallic component that melts to open a circuit. Fuses detect excess current to prevent overheating in a circuit.


A standard of measurement used for determining the diameter of wire. The gauge of a wire affects its resistance.


A device that converts mechanical energy into electrical energy. Generators operate on the principle of magnetic induction.


A soft, yellow metal that is highly conductive. Gold is often used as a conductor in electronic devices.


A source of zero electrical potential, such as the earth or another large conducting body. A ground absorbs electrical currents.


Any material that exhibits high resistance to electrical current. Insulators include rubber, plastic, and wood.


A conductive device within a circuit to which other components can be attached. A lead has either a negative or positive charge.


A component in a circuit that converts electricity into light, heat, or mechanical motion. Loads include light bulbs, appliances, and machines.

magnetic flux

The force that surrounds a magnet and exhibits the powers of attraction and repulsion. Magnetic flux is described as imaginary lines of force that exit the magnet's north pole and return to its south pole.

magnetic induction

The use of magnets to cause voltage in a conductor. Magnetic induction occurs whenever a conductor passes through magnetic lines of flux.

mechanical energy

Power that is produced by some force of motion, such as water power, wind power, gas power, or human power. Mechanical energy can transform into electricity with the use of magnetic induction.


The component of a watch that vibrates to help it keep time. An oscillator consists of a slice of quartz that vibrates when current is applied to it.

overcurrent device

A component that protects circuits from excess current flow to prevent fires. Overcurrent devices include fuses and circuit breakers.


To release or remove electrons from an atom, an ion, or a molecule. Oxidation is used to rank the metals on the electromotive series.


A conductor that directs electricity in a circuit. The path is often copper wire.


An electrical charge produced by mechanical manipulation of a crystal. Piezoelectricity can be produced by stretching, compressing, striking, or twisting a crystal.

PN diode

A semiconductor diode that has one positively charged side and one negatively charged side. The PN diode allows current to flow only from the negative side to the positive side.


Having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current flows.

pole pieces

A magnet in a device such as a generator that helps create the magnetic field. Pole pieces facilitate magnetic induction.

primary cell battery

A battery that cannot be recharged. Primary cell batteries are usually dry-cell.

pure semiconductor

A semiconductor that contains no added impurities. Pure semiconductors are less resistant than insulators but more resistant than conductors.


A manual control device that opens or closes a circuit when pressed. Pushbuttons attach to contacts that control the circuit.


A hard, piezoelectric crystalline mineral. Quartz is made of silica.


A device used in circuits to limit current flow. Resistors can be used to prevent overheating.

Rochelle salt

A piezoelectric crystalline compound. Rochelle salt is often used in the needle on a phonograph.


A chemical compound with a crystalline structure. Salt mixtures are conductive electrolytes.

secondary cell battery

A rechargeable battery. Secondary cell batteries are usually wet-cell.


A material that restricts electrons but still allows them to flow. Semiconductors, such as silicon, have more electrical conductivity than insulators but less than conductors.


A type of covering that completely wraps or encases an object. Sheathing made of metal is sometimes found under plastic insulation on a wire.

short circuiting

The condition in which current takes a shorter, unintended path between two conductors. Short circuiting causes excess current flow.


A lustrous, gray semi-metallic material. Silicon is a semiconductor.


A soft, gray-white metal that has the highest electrical conductivity of all metals. Silver is often used as a conductor in electronic devices.


The device that provides electrical power to a circuit. The source is the origin of electricity, such as a battery.


A device that opens and closes a circuit. Switches control when a circuit is energized.


A conductive device within a circuit to which other components can be attached. Terminals have a negative or positive charge.


A plastic that may be repeatedly heated, shaped, and cooled without damage. Thermoplastic is often used to cover electrical wires.

time-delay fuse

An overcurrent device that allows a specific amount of heat to build up before it opens the circuit. Time-delay fuses are used when short bursts of overcurrent are acceptable.

valence shells

The outermost orbit of electrons in an atom. Valence shells can have only eight electrons.

wet-cell battery

A device containing a liquid electrolyte that converts chemical energy into electrical energy. Wet-cell batteries include many secondary cell batteries.