17.0     ELECTRIC CURRENT

Electric current refers to the flow of electricity in an electronic circuit, and to the amount of electricity flowing through a circuit. It is represented by ‘I’ and measured in Ampere (A).

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METHODS OF PRODUCTION OF ELECTRIC CHARGE 

• By Friction: When two different materials are rubbed together, electrons may transfer from one material to another, resulting in one body becoming positively charged and the other negatively charged.
• By Contact: When a charged body touches a neutral body, electrons can transfer, causing the neutral body to become charged.
• By Induction: A charged body can induce a charge in a neutral body without direct contact. The neutral body becomes polarized, and if grounded, it can gain a net charge.

ELECTROSCOPE: An electroscope is a device used to detect electric charge.

COULOMB’S LAW: It states that the force (F) between two-point charges (q1 and q2) is directly proportional to the product of the charges and inversely proportional to the square of the distance (r) between them.

ELECTRIC FIELD (E): The electric field is defined as the force per unit charge experienced by a positive test charge placed in the field           E = F/q

ELECTRIC POTENTIAL (V): The electric potential at a point in an electric field is the work done in bringing a unit positive charge from infinity to that point.

V = W/q

FIELD INTENSITY (E): It is a vector quantity that represents the force experienced by a unit positive charge in an electric field.

POTENTIAL (V): It is a scalar quantity that indicates the potential energy per unit charge at a point in the field.

POTENTIAL DIFFERENCE (ΔV): The difference in electric potential between two points in an electric field, which is the work done to move a charge between those points.

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          17.1     CAPACITORS

A capacitor is an electronic component that stores electrical energy in an electric field. It consists of two conductive plates separated by an insulating material called a dielectric.

BASIC STRUCTURE OF A CAPACITOR

• Plates: Conductive materials (often metal) that store charge.
• Dielectric: An insulating material between the plates that increases the capacitor’s ability to store charge.

PLATE CAPACITORS: A parallel plate capacitor consists of two conductive plates separated by an insulating material (dielectric).

The capacitance of a parallel plate capacitor is determined by the area (A) of the plates, the distance (d) between them, and the dielectric constant (ε) of the material between the plates.

FUNCTIONS OF CAPACITORS

• They Store electrical energy for later use.
• They Smooth out fluctuations in the power supply (filtering).
• They Block direct current (DC) while allowing alternating current (AC) to pass.

PARALLEL CAPACITANCE (C): It is defined as the amount of charge (Q) stored per unit voltage (V) across the capacitor:

C = Q/V              (measured in Farads (F))

Where       1 Farad = 1 Coulomb/Volt.

RELATIONSHIP BETWEEN CAPACITANCE, AREA, SEPARATION OF PLATES, AND MEDIUM

The capacitance of a parallel plate capacitor can be expressed as:

C = ε * (A/d)

Where                 C =Capacitance,

ε = Permittivity of the dielectric material,

A = Area of one of the plates,

d = Separation between the plates.

CAPACITORS IN SERIES AND PARALLEL

• Capacitors in Series: The total capacitance (C_Total) is given by:

1/C_Total = 1/C₁ + 1/C₂ + 1/C₃… + 1/C_n

The charge (Q) is the same across all capacitors, but the voltage divides.

• Capacitors in Parallel: The total capacitance (C_Total) is given by:

C_Total = C₁ + C₂ + C₃ … + C_n 

The voltage (V) is the same across all capacitors, but the charge divides.         

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ENERGY STORED IN A CAPACITOR: The energy (U) stored in a capacitor is given by the formula:

U = (½)CV²

Where:      U = Energy stored,

C = Capacitance,

V = Voltage across the capacitor.

          17.2     ELECTRIC CELL

Electric cell is a device that converts chemical energy into electrical energy through electrochemical reactions.

KEY COMPONENTS OF AN ELECTRIC CELL

• Anode: The electrode where oxidation occurs (loss of electrons).
• Cathode: The electrode where reduction occurs (gain of electrons).
• Electrolyte: A substance (usually a liquid or gel) that contains ions and conducts electricity, allowing the movement of charge between the electrodes.

TYPES OF ELECTRIC CELLS

• Voltaic (Galvanic) Cells: Generate electricity from spontaneous chemical reactions (e.g., batteries).
• Electrolytic Cells: Use electrical energy to drive non-spontaneous chemical reactions (e.g., electrolysis).

17.3     SECONDARY CELLS

Secondary cells, also known as rechargeable batteries, can undergo reversible chemical reactions, allowing them to be recharged and used multiple times.

TYPES OF SECONDARY CELLS

• Lead-Acid Accumulator: Used in vehicles; consists of lead dioxide (positive plate) and sponge lead (negative plate) in sulfuric acid(H²SO⁴) , Rechargeable and provides high current.
• Nickel-Iron (NiFe) Cell: Uses nickel oxide and iron as electrodes in an alkaline electrolyte, known for durability and long life.
• Lithium-Ion Cell: Common in portable electronics; uses lithium compounds as electrodes, high energy density and lightweight.

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17.4     PRIMARY CELLS

Primary cells are electrochemical cells that generate electricity through irreversible chemical reactions. Once the reactants are used up, the cell cannot be recharged.

TYPES OF PRIMARY CELLS

• Daniel Cell: A type of voltaic cell consisting of a copper sulphate solution and a zinc electrode. The reaction involves zinc oxidizing and copper ions reducing, generating electricity.
• Leclanché Cell
• Wet Leclanché Cell: Contains a zinc anode, carbon cathode, and ammonium chloride solution as electrolyte.
• Dry Leclanché Cell: A variation where the electrolyte is in a paste form, making it portable and leak-proof.

          17.5     TYPES OF ARRANGEMENT OF CELL

• Series Arrangement: Cells are connected end-to-end, increasing the total voltage while the current remains the same.

Total Voltage = V₁ + V₂ + V₃ + …

• Parallel Arrangement: Cells are connected side-by-side, increasing the total current while the voltage remains the same.

Total Current = I₁ + I₂ + I₃ + …