Electric Current: Sources, Generation, and Power

Understanding Electric Current

Electric current is the flow or passage of electric charge, typically electrons, along a conductor. This flow is driven by a potential difference (voltage) often created by a power generator.

The conventional direction of current is considered from a higher potential (positive pole) to a lower potential (negative pole), although electrons actually move in the opposite direction (from negative to positive).

Electric Power Generators

These are devices that create an electrical current by maintaining a potential difference between the ends of a conductor.

Cells and Batteries (Chemical Generators)

These devices produce direct current (DC) electricity from chemical reactions. They are composed of two elements called electrodes (positive and negative) and a substance called an electrolyte. The electrolyte facilitates the chemical reaction that maintains the potential difference between the electrodes.

Primary Cells (Non-Rechargeable Batteries)

These are non-rechargeable DC generators that become depleted as their internal components are consumed or degrade during the chemical reaction.

Saline Cells

These typically comprise a carbon rod (positive electrode), a zinc casing (negative electrode), and an electrolyte paste (e.g., ammonium chloride).

Alkaline Batteries

Similar to saline cells but generally offer higher capacity. They use manganese dioxide (positive electrode), powdered zinc (negative electrode), and potassium hydroxide (electrolyte).

Button Cells

These are small, coin-shaped cells used in compact electronic devices like watches and calculators, where larger batteries cannot fit.

Battery Packs

These consist of multiple cells connected together, often in series, to provide a specific voltage. For example, a 4.5 V pack might contain three 1.5 V cells in series. Terminal polarity is usually indicated (+ for positive, - for negative).

Secondary Cells (Rechargeable Batteries/Accumulators)

These are DC generators whose chemical reactions can be reversed by applying an external current, allowing them to be recharged and reused multiple times.

Common types include:

• Lead-acid batteries
• Nickel-cadmium (NiCd) batteries
• Nickel-metal hydride (NiMH) batteries
• Lithium-ion (Li-ion) batteries

Mechanical Generators

These generate electricity using mechanical systems, often involving the principles of electromagnetic induction (see Electromagnetic Generators).

Solar Cells (Photovoltaic Cells)

These devices convert solar energy directly into electricity by exploiting the photovoltaic effect in semiconductor materials.

Electromagnetic Generators

The area of influence of a magnet is called a magnetic field.

Electromagnetic generators produce electric current through a process called electromagnetic induction. An induced current is created when a conductor moves within a magnetic field or when a magnet moves relative to a coiled conductor. Key components include:

• Rotor: The rotating part.
• Stator: The stationary part.

Electromagnetic generators producing alternating current (AC) are called alternators.

Electromagnetic generators producing direct current (DC) are known as dynamos (though DC is often generated today by alternators combined with rectifiers).

Electric Power

Electric power is the rate at which electrical energy is transferred or work is done by an electric circuit, measured per unit of time.

The standard unit of electric power is the Watt (W). One watt is defined as the power resulting from one ampere (A) of current flowing under a potential difference of one volt (V).

Energy Transformations

Electrical energy can be converted into other forms:

• Mechanical energy: Produced when current passes through an electric motor.
• Heat energy: Generated when current flows through a resistance (e.g., in a heater).
• Light energy: Emitted when current passes through a lamp or LED.