Electrical Energy (E)
Definition of electrical energy: Electrical energy is the ability or capacity of electric charges—tiny particles that make up electricity—to do work. This work happens when the charges move through a conductor like a wire in a circuit. For example, when you turn on a flashlight, electrical energy flows through the wires and makes the bulb light up.
Energy transformation: Electrical energy is very useful because it can be changed, or transformed, into many other types of energy. For example, in a heater, it becomes heat energy; in a lamp, it becomes light energy; in a speaker, it turns into sound; in a fan, it becomes movement (called mechanical energy); and in a battery charger, it even becomes chemical energy.
Charge relationship: The amount of electrical energy produced or used in a circuit depends on several factors: how much electric charge is moving, the voltage (which is like the push that moves the charges), the current (which is how fast the charges are moving), the resistance (how much the circuit parts slow the charges down), and how long the electricity flows.
Basic formula (VQ): We can calculate electrical energy using a formula: E = VQ. This means that energy (E) equals voltage (V) times charge (Q). If the voltage is strong and a lot of charge moves, more energy is transferred.
Current-time formula (VIt): Another way to find electrical energy is using E = VIt. This comes from the idea that Q = It, where current (I) times time (t) gives us charge. So, this formula is useful when we know the current and how long it flows.
Resistive formula (I²Rt): We can also use Ohm’s Law (V = IR) to change the formula and get E = I²Rt. This means the energy used in a resistor increases when the current is higher, the resistance is greater, and the electricity flows for a longer time.
Voltage-time formula (V²t/R): Another version is E = V²t/R. This comes from replacing current in the VIt formula using I = V/R. It’s a helpful formula when we know the voltage and resistance in the circuit.
Unit of energy: Energy is measured in a unit called the joule (J). One joule is a small amount of energy. It’s like the energy needed to push a book across a table using a small force.
Definition of 1 joule: One joule equals the energy used when a force of 1 newton moves an object a distance of 1 meter. So, 1 J = 1 N·m.
Practical unit (kWh): In the real world, especially for things like electric bills, energy is often measured in kilowatt-hours (kWh), because a joule is a very small unit for large devices.
kWh conversion: One kilowatt-hour is equal to 3.6 million joules (written as 3.6 × 10⁶ J). This means if a 1000-watt device runs for one hour, it uses 1 kWh of energy.
Application of energy: Electrical energy is everywhere in our daily lives. It powers the lights in our rooms, the refrigerator in the kitchen, and the machines in big factories. It is one of the most important and widely used forms of energy in the modern world.
Electrical Power (P)
Definition of power: Electrical power is a measure of how quickly energy is being used or produced. It tells us the rate at which energy flows. For example, a microwave oven uses power to heat food fast.
Power-energy link: Power helps us understand how fast electrical energy is being used. If something uses a lot of energy in a short time, it has high power. If it uses energy slowly, it has low power.
Energy-time formula (E/t): The formula for power is P = E/t. This means power (P) equals energy (E) divided by time (t). It shows how much energy is used per second.
Voltage-current formula (VI): Another formula is P = VI. Here, power equals voltage (V) multiplied by current (I). This shows how much energy is being used each second based on the push (voltage) and flow (current) of charges.
Current-resistance formula (I²R): Using Ohm’s Law again (V = IR), we can get another formula: P = I²R. This version is useful if we know the current and the resistance in the circuit.
Voltage-resistance formula (V²/R): We can also write power as P = V²/R. This is handy when we know the voltage and resistance, but not the current.
Unit of power: Power is measured in watts (W). One watt means one joule of energy is used every second. So, 1 W = 1 J/s.
Small unit note: A watt is a small amount of power. For example, an LED night light may use just 1 or 2 watts.
Higher unit (kW): For bigger electrical devices like air conditioners or washing machines, we use kilowatts (kW). One kilowatt equals 1000 watts.
Application of power: Power ratings on devices help us choose which one is suitable for our needs. They tell us how much energy the device uses every second, helping us avoid using too much power and overloading the circuit.
Efficiency
Efficiency definition: Efficiency shows us how well a device turns input energy into useful output energy. A high-efficiency device uses most of the energy it receives for the job it’s supposed to do, and wastes very little.
Output-input ratio: Efficiency compares the energy we get out of a device to the energy we put into it. The higher the output compared to the input, the more efficient the device is.
Efficiency formula: We calculate efficiency using these formulas: (Power output / Power input) × 100% or (Energy output / Energy input) × 100%. The result is a percentage that shows how efficient the device is.
Expression unit: Efficiency is usually written as a percentage. For example, if a fan is 80% efficient, it means 80% of the energy is used to move air, and 20% is lost (maybe as heat).
Factors affecting efficiency: Efficiency can be affected by heat loss, sound, friction, or other energy losses. These things reduce the amount of energy used for useful work.
Ideal efficiency: A perfectly efficient machine would have 100% efficiency, meaning all the input energy is turned into useful output. But in real life, no machine can reach exactly 100%.
Real-world losses: All real machines lose some energy. For example, electric motors often get warm because part of the electrical energy is turned into heat.
Design consideration: Engineers and designers work hard to make devices more efficient. Better efficiency means saving energy, reducing electricity costs, and helping the environment.