Fundamentals of Electricity: Quantities, Circuits, and Measurement
1 – Basic Electrical Quantities
The fundamental quantities that characterize electrical power are voltage, current, resistance, and power.
Voltage
The energy with which a generator is able to push electrons through a circuit is called voltage or electromotive force (EMF).
Voltage is also known as potential difference (PD) and is measured in volts (V).
Electric Current
Electric current is the rate of flow of electric charge through a circuit per unit time.
Electric current, also called intensity, is measured in amperes (A), in honor of the French physicist André-Marie Ampère.
An electric current of one ampere (1A) flows when one coulomb (1C) of charge passes a point in a circuit in one second (1s). The unit of electric charge is the coulomb (C). Therefore: 1A = 1C/1s.
Electrical Resistance
Electrical resistance is the opposition offered by a material to the passage of electric current. The unit of resistance is the ohm (Ω), in honor of the German scientist Georg Ohm.
Power
Power is the ability of a receiver to perform its function more effectively and/or faster, and is measured in watts.
Power indicates a machine’s ability to perform its function more or less quickly. All electrical devices convert energy, with some performing their function faster or producing brighter light than others.
The power of a receiver is directly related to the voltage and current with which it is supplied in the circuit. Power is measured in watts (W) in honor of James Watt. The kilowatt (kW), equivalent to 1000W, is also widely used.
Ohm’s Law
The intensity of electric current that flows through a circuit is directly proportional to the applied voltage and inversely proportional to the resistance offered.
In a circuit, three basic quantities (voltage, resistance, and current) are closely interrelated. This relationship is known as Ohm’s Law, named after Georg Ohm.
It is expressed as follows: I = V / R, where I is the intensity (current) expressed in amperes (A), V is the voltage in volts (V), and R is the resistance in ohms (Ω).
2 – Series and Parallel Circuits
These elements can be connected in different ways:
- Series connection
- Parallel connection
- Mixed connection
Series Connection
When different elements in a circuit are connected one after another so that the same electrical current flows through them, they are said to be connected in series.
Series Connection of Loads
In a series connection, if one lamp fails (e.g., ‘melts’ or breaks), the circuit is interrupted.
The characteristics of a series circuit are:
- The current flowing through each load is the same. Therefore, if one load is disconnected for any reason, the circuit is opened, interrupting the flow and causing all other loads to stop working.
- The generator’s voltage is shared among the loads, with the voltage across each load being directly proportional to its resistance.
Connecting Batteries in Series
Batteries are connected in series by connecting the positive terminal of one battery to the negative terminal of the next.
The current must pass through each battery. The total voltage supplied to the circuit is the sum of the individual voltages of each battery. Therefore, connecting batteries in series is used to increase the total voltage supplied to a circuit.
Parallel Connection (Shunt)
When elements in a circuit are connected so that from a connection point the current splits among the elements and then reunites at the output, these elements are said to be connected in parallel.
Parallel Connection of Loads
When examining parallel circuits, we can observe the following characteristics:
- If one load stops working due to an anomaly, the others continue to operate.
- Each load receives the same voltage, which is equal to the generator’s voltage.
Connecting Batteries in Parallel
The voltage supplied to the circuit will be equal to that of a single battery, but the total current supplied can be higher.
In a circuit powered by batteries connected in parallel, the autonomy of the batteries increases, as the energy consumed by the circuit is shared equally among all batteries.
3 – Measurement of Electrical Quantities
There are devices for measuring various electrical quantities in a circuit: voltmeters for voltage, ammeters for current, ohmmeters for resistance, and wattmeters for power.
These measuring devices can be analog or digital.
Voltmeter
To measure voltage, voltmeters are used. A voltmeter is a device that has two clamps or terminals, which are connected in parallel across the two points in the circuit where the voltage is to be measured.