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Circuits

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Circuits

An electric circuit is a set of electronic components that are connected. Sources, ground, resistors, and other devices make up an electric circuit. A circuit is a route through which electrons travel in a wire, making a closed loop of an electrical network.

What are the basic components of a circuit?

The basic circuit components include resistors, transistors, inductors, diodes, switches, capacitors, ground, and other sources. The conductive wires or traces connect all the components to each other and form a loop for the current to flow through.

Component
Description
Transistor
A semiconductor electronic component that may be used to amplify, generate, or switch electrical signals or power in circuits.
Inductor
Also known as the coil or choke. It is made from a coil of insulated wire and is commonly used in switched-mode power systems to create direct current (DC).
Diode
A semiconductor device that functions as a one-way switch for current. It lets current flow freely in one direction whilst significantly restricting current flow in the other direction.
Switch
A component that manages the flow of electric current inside a circuit.
Capacitor
A type of electronic component that stores potential energy in the form of electricity. Capacitors store potential energy by holding positive and negative energy on two conductive plates separated by a dielectric material. This produces a potential difference between the two plates.
Ground
The reference point from which voltages are measured. At the ground point, the voltage value is zero.
Sources
Sources are the components that supply current, voltage, or power.
Resistor
A two-terminal passive electronic component that acts as a circuit element by implementing electrical resistance.
Measuring components
These are mainly referred to as voltmeters and ammeters.
The voltmeter is a device that measures the voltage differences between two points in an electric circuit. The ammeter is a component that measures electric current in amperes, either direct or alternating.

Below we focus on resistors and sources for you to get the fundamental knowledge about electrical circuits.

Resistors in circuits

A resistor is a two-terminal passive electronic component that acts as a circuit element by implementing electrical resistance. Resistors are used in electronic circuits for various purposes, including reducing current flow, adjusting signal levels, dividing voltages, biassing active components, and terminating transmission lines.

Circuits Symbols of a resistor StudySmarterThe two symbols for a resistor in a circuit, Oğulcan Tezcan – StudySmarter Originals

Here is Ohm’s law for calculating the resistance:

V stands for voltage in volts, I is for current in amperes, and R is for resistance in ohms.

The variable resistor is another component that allows us to control how much current flows across a circuit. It operates by moving a wiper terminal over a resistive substance, which is usually a thin film, a chunk of carbon, or a resistive wire composed of nickel-chromium or tungsten alloys.

Circuits Symbol of a variable resistor StudySmarterThe symbol of a variable resistor in a circuit, Oğulcan Tezcan – StudySmarter Originals

Sources in circuits

Three types of sources are used in electric circuits: current source, AC (alternating current) voltage source, and DC voltage source.

  • A current source is an electronic component that either provides or absorbs electricity. There are two types of current sources: independent current source and dependent current source. While an independent current source delivers a continuous current, a dependent current source generates current proportional to another voltage or current in the circuit.
  • An AC power source is a device capable of supplying alternating power and frequency to a load. An AC power’s graph has the shape of a sine wave where the amplitude is the maximum voltage in volts, and the frequency is measured by period per second.
  • DC voltage source is a device capable of supplying constant voltages and currents to the circuit.

Circuits Symbols of power sources StudySmarterThe symbols for a current source, AC power source, and DC voltage source, Oğulcan Tezcan – StudySmarter Originals

While the values you see next to the current source and the DC voltage source are constant, the value you see next to the AC power source is the value of the sine wave’s amplitude.

What are the types of circuits?

There are five main types of circuits: closed circuit, open circuit, short circuit, series circuit, and parallel circuit. Each of these is designed to create a conductive path for current flow.

  • An open circuit is a circuit that has no current flowing through it. The circuit’s continuity is interrupted, and the current does not flow as a result. An open circuit is any circuit that does not pass current when a potential difference is created, and its resistance is infinite.
  • A closed circuit is a complete electrical connection around which current flows or circulates. A closed circuit is formed when a succession of electrical wires connects to each other and completes a circuit, allowing electricity to flow from one end of the circuit to the other.
  • A short circuit is an improper connection between two nodes with voltages that are supposed to be different but aren't. In an ideal short circuit, this implies that there is no resistance and no voltage drop across the link. The outcome in actual circuits is a connection with nearly no resistance. When there is almost no resistance, all the current going through the conductive wire travels through the short circuit and reaches high levels. This can cause the conductive wire to burn out.

The section below focuses on series circuits and parallel circuits for you to get the fundamental knowledge about electric circuits.

Series circuit

A series circuit is a circuit in which the entire current passes through all components without dividing.

Circuits Resistor series circuit StudySmarterAn example diagram of a simple series circuit Oğulcan Tezcan – StudySmarter Originals

Calculating the total voltage in a series circuit

The same amount of current goes through all the components without dividing in a series circuit. To calculate the total voltage in a series circuit, we use this equation:

V is the voltage value of the DC voltage source. VR1, VR2, and VR3 are the voltage values of the resistors.

Calculating the total resistance in a series circuit

Here is the equation for calculating the total resistance:

RTotal is the total value of resistance in ohms. R1, R2, and R3 are the resistance values in ohms.

Calculating the total current in a series circuit

The total current in series circuits is the same value as the individual current for all components. You can define it as:

I1, I2, and I3 are the values of the current going through R1, R2, and R3 in amperes.

Parallel circuit

A parallel circuit has branches that divide the current so that just a portion of it travels through each branch. In a parallel circuit, the voltage (or potential difference) between each branch is the same, but the currents may vary.

Circuits Resistor parallel circuit StudySmarterAn example diagram of a basic parallel circuit, Oğulcan Tezcan – StudySmarter Originals

Calculating the total voltage in a parallel circuit

The total voltage in parallel circuits is the same value as the individual voltage for all branches. You can define it as:

V is the voltage value of the DC voltage source. V1, V2, and V3 are the voltage values of the resistors on the different branches.

Calculating the total resistance in a parallel circuit

To calculate the total resistance in a parallel circuit, we use this equation:

RTotal is the total value of resistance in ohms. R1, R2, and R3 are the resistance values of the resistors in ohms.

Calculating the total current in a parallel circuit

Here is the equation we use for calculating the total current in a parallel circuit:

I1, I2, and I3 are the values of the current going through R1, R2, and R3 in amperes.

Calculating an individual resistance’s current in a parallel circuit

If you want to calculate an individual resistance’s current in a parallel circuit, there is a shortcut! Let’s calculate R1’s current from the above diagram.

Let us say the total resistance RTotal of R2 and R3 is Rp, which we can find as shown below.

We can then put this value in our shortcut equation and find the current value of R1. This is also known as a current divider.

The total current in series circuits is the same value as the individual current for all components.

The total voltage in parallel circuits is the same value as the individual voltage for all branches.

Circuits - key takeaways

  • An electrical circuit is a collection of interconnected electronic components.
  • The basic components of an electric circuit are sources, ground, resistors, inductors, diodes, capacitors, switches, and transistors.
  • The five main types of electric circuits are closed circuits, open circuits, short circuits, series circuits, and parallel circuits.
  • An open circuit is a circuit that has no current flowing through it because of an interruption.
  • A closed circuit is a complete electrical connection around which current flows or circulates.
  • The main difference between a series and parallel circuit is that whilst the current is not divided in the series circuit, it is divided into branches in a parallel circuit.

Frequently Asked Questions about Circuits

A circuit breaker is a safety device that protects an electric circuit when there is too much current or a short circuit. 

A series circuit is a circuit in which the entire current passes through all of the components without dividing.

A parallel circuit is a circuit that has branches that divide the current so that just a portion of it travels through each branch.

An electric circuit is a collection of interconnected electronic components.

A short circuit is an improper connection between two nodes of an electric circuit with voltages that are supposed to be different but aren’t.

Final Circuits Quiz

Question

Find the total resistance for the circuit below.

Circuits A basic series and parallel circuit StudySmarterA basic series and parallel circuit, Olğucan Tezcan - StudySmarter Originals

Hint: notice how R2 and Rare connected in series and Ris connected parallel to R2 and R3.

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Answer

2 ohms.

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Question

What are the two main measuring devices in electric circuits?

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Answer

Voltmeters and ammeters.

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Question

The voltage value at a ground point is what?


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Answer

Zero.

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Question

Which equation is used to find a capacitor’s current?


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Answer


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Question

What is the symbol for electric current?


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Answer

I

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Question

What is the main use of a switch in electric circuits?


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Answer

To stop and start the current flow.

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Question

Ideally, how much resistance does a diode show when the current is flowing from its anode to its cathode?


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Answer

A resistance of zero.

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Question

In reality, what happens if the current flowing through a diode’s anode to the cathode can’t reach its threshold level?


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Answer

The current can't flow through.

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Question

Which equation is used to find an inductor’s voltage value?


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Answer


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Question

What is the voltage difference between a bipolar junction transistor’s base and emitter terminals?


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Answer

0.7 volts.

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Question

Find the current value of R3 in amperes from the circuit below.

Circuits A basic parallel circuit StudySmarterA basic parallel circuit, Olğucan Tezcan - StudySmarter Originals

Hint: you should find the total resistance and current first, then use the equation for the current divider.

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Answer

5A.

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Question

Which equation is used to find a transistor’s emitter terminal’s current value?


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Answer


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Question

What is Ohm’s law for the resistor in mathematical form?


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Answer


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Question

What is the name of the positive pole of a component?


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Answer

The anode.

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Question

What is the name of the negative pole of a component?


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Answer

The cathode.

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Question

What is the total resistance of the circuit below?

Circuits A basic series circuit StudySmarterA basic series circuit, Olğucan Tezcan - StudySmarter Originals

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Answer

10 ohms.

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Question

Ideally, what resistance value does a diode show when the current is trying to flow from its cathode to its anode?


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Answer

The resistance value of the diode should be infinite.

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Question

What is the total current of the circuit below?

Circuits A basic series circuit StudySmarterA basic series circuit, Olğucan Tezcan - StudySmarter Originals

Hint: find the total resistance first, then use the V = I⋅R equation.

Show answer

Answer

5A.

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