In an electrical circuit, charges move which creates an electrical current. In other words, there is a displacement of the negative charges carried by electrons.
Current intensity, or amperage, is the amount of electrical charge flowing through a specific point in an electrical circuit each second.
Current intensity is used to measure the speed at which electrons flow through a specific point in the electrical circuit.
The formula below is used to determine the current intensity in an electrical circuit.
|I=\dfrac{q}{\Delta t}|
where
|I:| current intensity |\text {(A)}|
|q:| amount of charge |\text {(C)}|
|\Delta t:| time interval |\text {(s)}|
An ammeter measures current intensity.
What is the current intensity in a circuit if |\text {1 600 C}| has been moving for a period of |\text {40 s}|?
||\begin{align} q &= \text{1 600 C} &\Delta t &= \text {40 s} \end{align}||
||\begin{align} I=\dfrac{q}{\Delta t} \quad \Rightarrow \quad
I&=\dfrac{\text {1 600 C}}{\text {40 s}}\\
&= \text {40 A}
\end{align}||
The current intensity in this circuit is |\text {40 A}.|
Intensity is measured in amperes |\text {(A)},| a unit that represents the amount of charge in relation to time. One ampere is equal to the movement of one coulomb per second in an electrical circuit.
||\text {1 A}=\dfrac{\text {1 C}}{\text {1 s}}||
Potential difference, also known as voltage, is the amount of electrical energy transferred per unit of charge between two points in an electrical circuit.
When electric charges move along an electrical circuit, they transfer their energy to the various components of the circuit (resistor, light source, etc.). By measuring the potential difference, it is possible to determine just how much energy is transferred.
|V=\dfrac{E}{q}|
where
|V:| potential difference |\text {(V)}|
|E:| energy transferred |\text {(J)}|
|q:| amount of charge |\text {(C)}|
A voltmeter measures potential difference.
What is the potential difference in a circuit if the energy transmitted by |\text {200 C}| is |\text {200 000 J}|?
||\begin{align} q &= \text{200 C} &E &= \text {200 000 J}
\end{align}||
||\begin{align} V= \dfrac{E}{q} \quad \Rightarrow \quad
V&= \dfrac{\text {200 000 J}}{\text {200 C}}\\
&= \text {1 000 V}
\end{align}||
The potential difference in the electrical circuit is |\text {1 000 V}.|
The potential difference is measured in volts |\text {(V)},| a unit that represents the amount of energy in relation to the amount of charge.
||\text {1 V}=\dfrac{\text {1 J}}{\text {1 C}}||
Electrical resistance is the ability of a material to resist the flow of an electrical current.
In an electrical circuit, the resistor converts electrical energy into another form of energy. For example, the resistors in a toaster convert electrical energy into thermal energy. The greater the resistance, the more the flow of the electrical current is blocked and the greater the transformation of energy.
A multimeter measures electrical resistance.
Resistance is measured in ohms |(\Omega),| a unit that represents the ratio between the potential difference and the intensity.
||1\ \Omega=\dfrac{\text {1 V}}{\text {1 A}}||
Using Ohm’s law, it is possible to calculate the resistance of an electrical circuit.
Four factors influence how resistant a substance is to the flow of electrical current.
Length
The longer a wire in an electrical circuit, the greater its resistance.
Using a short hose to water a garden will cause the water to shoot out at a much higher pressure, because it does not have as far to travel and it has less opportunity to collide with the walls of the hose. A short hose also means a short distance from the tap, reducing the chances of a leak.
The same is true for an electrical circuit. A shorter electrical wire reduces the resistance because there is limited contact between the electrons and the atoms of the conductor. The resistance of a wire is directly proportional to its length.
Size (Gauge)
In an electrical circuit, the smaller the diameter of the wire, the greater the resistance.
When putting out a fire, it is better to use a fire truck hose than a garden hose because more water will flow through the fire truck hose. Electrical circuits follow the same principle: a larger wire allows more electrical charge to flow through. The resistance of a wire is inversely proportional to its sectional area, meaning the square of its diameter (if the wire is cylindrical).
Type of material
In an electrical circuit, an electrical current will flow more freely through metals than through metalloids and nonmetals.
Some metals, including silver, copper, gold and aluminum, are better conductors than others, like iron and lead, but overall, metals are better conductors than metalloids and nonmetals.
Temperature
In an electrical circuit, the hotter the wire, the greater the resistance.
When a substance is very hot, its atoms move rapidly. This means that electrons trying to move through the electrical circuit are more likely to collide with these atoms.
In a colder substance, the atoms move very little. This clears the way for the electrons so they can move through the substance, encouraging the flow of the electrical current and decreasing electrical resistance.
In an electrical circuit, conductance refers to how well an electrical current can flow through it. Conductance is the opposite of resistance and is measured in siemens |(\text{S}).|
|R=\dfrac{1}{G}|
or
|G=\dfrac{1}{R}|
where
|R:| resistance |(\Omega)|
|G:| conductance |(\text{S})|
A resistor has a value of |40\ \Omega.| What is the conductance?
||\begin{align}G=\dfrac{1}{R}\quad \Rightarrow \quad G &= \dfrac{1}{40\ \Omega} \\ &= \text {0.025 S} \end{align}||
The conductance of this resistor is |\text {0.025 S}.|