Electric Charges and Current Electricity

Electric Charges and Current Electricity

Electricity plays a crucial role in our daily lives, from powering our homes to enabling advanced technological innovations. This article provides a comprehensive overview of electric charges, production of charges, electric circuits, current electricity, Ohm’s Law, electrical power, and resistor arrangements, complete with worked examples for better understanding.

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1. Electric Charges

Electric charge is a fundamental property of matter that causes it to experience a force in an electric field. It results from the movement of electrons from a charged body to an uncharged body.

Types of Electric Charges

Electric charges are classified into two types:

1. Positive charge (+) – This occurs when an object loses electrons.
2. Negative charge (-) – This occurs when an object gains electrons.

Production of Electric Charges

Electric charge can be produced by the following methods:

1. Friction: When two different insulating materials are rubbed together, electrons transfer from one material to another.
2. Induction: Producing an electric charge without direct contact with a charged object.
3. Contact: Direct transfer of charge through physical touch.

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2. Conductors and Insulators

Conductors

Conductors allow free movement of electrons. Examples include metals, graphite, salt solutions, and the human body.

Insulators

Insulators restrict the flow of electrons. Examples include plastic, rubber, glass, and silk.

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3. Electroscope

An electroscope is an instrument used for detecting and testing small electric charges. It consists of:

• A metal rod attached to a thin gold or aluminum leaf.
• A brass cap or disc at the top.
• An insulated case to prevent external interference.

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4. Lightning and Lightning Conductors

Lightning is a discharge of static electricity in the atmosphere. Lightning conductors are used to safely direct this discharge into the ground.

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5. Electric Circuits

An electric circuit is a closed path through which electric current flows. It consists of:

• A power source (e.g., battery, generator)
• Conducting wires
• A load (e.g., bulb, motor, resistor)
• A switch to control current flow

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6. Production of Electric Current

Electric current can be generated through:

1. Chemical Energy: Batteries and voltaic cells.
2. Heat Energy: Thermocouples.
3. Mechanical Energy: Generators and dynamos.
4. Solar Energy: Solar panels.

Defects of Simple Cells

1. Polarization: Formation of hydrogen bubbles around electrodes.
2. Local Action: Unwanted reactions due to impurities in electrodes.

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7. Ohm’s Law

Ohm’s Law states that the current (I) flowing through a conductor is directly proportional to the voltage (V) across its ends, provided temperature and other physical factors remain constant.

$V = IR$

where:

• $V$ = Voltage (Volts)
• $I$ = Current (Amperes)
• $R$ = Resistance (Ohms)

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8. Electrical Power and Energy

Work Done in an Electric Circuit

$W = IVt$

where:

• $W$ = Work done (Joules)
• $I$ = Current (Amperes)
• $V$ = Voltage (Volts)
• $t$ = Time (Seconds)

Electrical Power

$P = IV$

or using Ohm’s law,

$P = I^2 R = \frac{V^2}{R}$

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9. Arrangement of Resistors

Resistors can be arranged in series, parallel, or a combination of both.

Resistors in Series

Total resistance in a series circuit is given by: $R_{total} = R_1 + R_2 + R_3 + ... + R_n$

The current remains the same across all resistors, but the voltage divides among them.

Resistors in Parallel

Total resistance in a parallel circuit is given by: $\frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + ... + \frac{1}{R_n}$

The voltage remains the same across all resistors, but the current divides among them.

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10. Worked Examples

Example 1: Calculating Current

A 12V battery supplies a current to a 6Ω resistor. Find the current.

$I = \frac{V}{R} = \frac{12}{6} = 2A$

Example 2: Electrical Energy Calculation

An electric heater with a resistance of 11Ω is connected to a 220V power source for 2 seconds. Find the energy consumed.

$W = \frac{V^2}{R} t = \frac{220^2}{11} \times 2 = 8800J = 8.8kJ$

Example 3: Resistors in Series

Three resistors of 4Ω, 6Ω, and 10Ω are connected in series. Find the total resistance.

$R_{total} = R_1 + R_2 + R_3 = 4 + 6 + 10 = 20Ω$

Example 4: Resistors in Parallel

Two resistors, 8Ω and 12Ω, are connected in parallel. Find the total resistance.

$\frac{1}{R_{total}} = \frac{1}{8} + \frac{1}{12} = \frac{3}{24} + \frac{2}{24} = \frac{5}{24}$

$R_{total} = \frac{24}{5} = 4.8Ω$

Example 5: Power Consumption

Find the power consumed by a device that draws 4A from a 240V source.

$P = IV = 4 \times 240 = 960W$

JAMB Exam Practice: Electric Charges & Current Electricity

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