Electrical energy is an important concept in physics and engineering, as well as a practical necessity for everyday life. Electrical energy can be converted from other forms of energy, such as chemical, mechanical, or nuclear energy, and vice versa. Electrical energy can also be stored in batteries, capacitors, or other devices, and used for various applications, such as lighting, heating, cooling, or communication.
Electrical energy is the energy that is stored or transferred by the movement of electric charges in an electric field. Electrical energy can be either potential energy or kinetic energy, depending on the position and motion of the charges. Electrical energy can be converted from other forms of energy, such as chemical, mechanical, or nuclear energy, and vice versa. Electrical energy can also be used for various applications, such as lighting, heating, cooling, or communication. The formula for electrical energy is:
\(\displaystyle E = P \times t\)
where E is the electrical energy in joules (J), P is the power in watts (W), and t is the time in seconds (s).
The unit of electrical energy is the joule (J), which is equivalent to one watt-second (W⋅s). However, for practical purposes, electrical energy is often measured in kilowatt-hours (kWh), which is equal to 3.6 megajoules (MJ). One kilowatt-hour is the amount of electrical energy consumed by a device that uses one kilowatt of power for one hour.
Some examples of electrical energy are:
- The electrical energy is stored in a battery, which can be used to power a device or a vehicle.
- The electrical energy generated by a solar panel, can be used to charge a battery or supply electricity to a grid.
- The electrical energy transferred by a lightning bolt, which can cause damage or ignite a fire.
- The electrical energy consumed by a light bulb, which can produce light and heat.
For example, if a device draws 100 W of power for 10 minutes, then the electrical energy consumed by it is:
\(\displaystyle E = P \times t = 100 W \times 10 \times 60 s = 60,000 J\)
Another way to calculate electrical energy is to use the formula:
\(\displaystyle E = V \times I \times t\)
For example, if a circuit has a voltage difference of 12 V and a current of 5 A for 10 minutes, then the electrical energy delivered by it is:
\(\displaystyle E = V \times I \times t = 12 V \times 5 A \times 10 \times 60 s = 36,000 J\)
Electrical energy in terms of electric potential at different points is the amount of work done by an external agent to move a unit charge from one point to another in an electric field. The electric potential difference between two points is the change in electric potential energy per unit charge when a charge is moved from one point to another. The electric potential difference is also called the voltage and is measured in volts (V).
One way to calculate the electric potential difference between two points is to use the formula:
\(\displaystyle V = \frac{\Delta U}{q}\)
where V is the electric potential difference in volts (V), \(\displaystyle\Delta U\) is the change in electric potential energy in joules (J), and q is the charge in coulombs (C).
For example, if a charge of 2 C is moved from a point with an electric potential of 10 V to a point with an electric potential of 5 V, then the electric potential difference is:
\(\displaystyle V = \frac{\Delta U}{q} = \frac{U_2 – U_1}{q} = \frac{(5 V \times 2 C) – (10 V \times 2 C)}{2 C} = -5 V\)
This means that the charge loses 10 J of electric potential energy when it is moved from the higher potential point to the lower potential point. The negative sign indicates that the charge moves in the direction of the electric field.
Another way to calculate the electric potential difference between two points is to use the formula:
\(\displaystyle V = W_{ext}/q\)
where V is the electric potential difference in volts (V), \(\displaystyle W_{ext}\) is the work done by an external agent in joules (J), and q is the charge in coulombs (C).
For example, if an external agent does 15 J of work to move a charge of 3 C from a point with an electric potential of 4 V to a point with an electric potential of 9 V, then the electric potential difference is:
\(\displaystyle V = W_{ext}/q = 15 J / 3 C = 5 V\)
This means that the charge gains 15 J of electric potential energy when it is moved from the lower potential point to the higher potential point. The positive sign indicates that the charge moves against the electric field.
Power
Electrical energy is the energy that is stored or transferred by the movement of electric charges in an electric field. Electrical power is the rate of energy transfer per unit time. Electrical power is related to electrical voltage and current, which are the measures of electric potential difference and electric charge flow, respectively. One of the basic formulas for electrical power is:
$$P = I V$$
where P is the power in watts (W), I is the current in amperes (A), and V is the voltage in volts (V). This formula shows that the power is equal to the product of current and voltage. The power can also be expressed as:
$$P = I^2 R$$
where $R$ is the resistance in ohms (Ω), or as:
\(\displaystyle P = \frac{V^2}{R}\)
These formulas show that the power is proportional to the square of the current or the voltage, and inversely proportional to the resistance. The resistance is a measure of how much a material or a device opposes the flow of current. The theory of power in electrical energy also involves the concepts of efficiency, power factor, and power loss.
Efficiency is the ratio of output power to input power, and it indicates how well a device or a system converts electrical energy into useful work or output. Power factor is the ratio of real power to apparent power, and it indicates how well a device or a system utilizes the supplied voltage and current. Power loss is the amount of power that is dissipated as heat or other forms of energy in a device or a system, and it reduces the efficiency and the power factor.
The theory of power in electrical energy has many applications in engineering, science, and technology, such as designing and operating electric generators, motors, transformers, transmission lines, and distribution networks. The theory of power in electrical energy also helps us understand the environmental and economic impacts of electrical energy production and consumption.
Electrical resistivity and electrical conductivity
Electrical resistivity and electrical conductivity are two related properties of a material that describe how well it resists or allows the flow of electric current. A material with high resistivity has low conductivity, and vice versa.
Electrical resistivity is a measure of how strongly a material opposes the flow of electric current. It depends on the nature and structure of the material, as well as the temperature and other factors. The SI unit of resistivity is ohm meter (Ω⋅m). The resistivity of a material can be calculated by using the formula:
$$\rho = \frac{RA}{l}$$
Electrical conductivity is a measure of how easily a material allows the flow of electric current. It depends on the number and mobility of the electric charges in the material, such as electrons or ions. The SI unit of conductivity is siemens per metre (S/m). The conductivity of a material can be calculated by using the formula:
$$\sigma = \frac{1}{\rho}$$
where \(\displaystyle\sigma\) is the conductivity and \(\displaystyle\rho\) is the resistivity.
Different materials have different resistivities and conductivities, depending on their type and composition. For example, metals have low resistivities and high conductivities, because they have many free electrons that can move easily. Insulators have high resistivities and low conductivities, because they have few or no free electrons. Semiconductors have intermediate resistivities and conductivities, that can be changed by doping or temperature.