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.

Here is Ohm’s law for calculating the resistance:

\[R =\frac{V}{I}\]

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.

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.

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.

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:

\[V = V_{R1}+V_{R2} + V_{R3}\]

V is the voltage value of the DC voltage source. V_R1, V_R2, and V_R3 are the voltage values of the resistors.

Calculating the total resistance in a series circuit

Here is the equation for calculating the total resistance:

\[R_{Total} = R_1 +R_2+R_3\]

R_Total 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:

\[I_{Total} = I_1 = I_2 = I_3\]

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.

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:

\[V = V_1 = V_2 = V_3\]

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:

\[\frac{1}{R_{Total}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}\]

R_Total 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:

\[I_{Total} = I_1 + I_2+I_3\]

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 R_Total of R₂ and R₃ is R_p, which we can find as shown below.

\[\frac{1}{R_P} = \frac{1}{R_2} + \frac{1}{R_3}\]

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.

\[I_1 = \frac{R_P}{R_1+R_P} \cdot I_{Total}\]