Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

This page supports the lesson note with a companion video and a short classroom-ready summary.

For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.

Performance objectives

• Define current, potential difference, and resistance.
• Apply Ohm's Law to solve problems.
• Draw and interpret circuit diagrams.
• Calculate total resistance in series and parallel circuits.
• Explain the difference between series and parallel circuits.

Lesson summary

Electricity is a fundamental aspect of modern life in South Africa. From powering our homes and schools during load shedding (a very real and relevant issue!), to enabling communication through cell phones and computers, understanding electric circuits is crucial. This week, we'll be focusing on the basics of electric circuits: what they are, how they work, and how to analyze them. Understanding these concepts will not only help you succeed in Physical Sciences but also empower you to understand and potentially troubleshoot everyday electrical issues in your homes and communities.

Lesson notes

2.1 Electric Current (I) Electric current is the rate of flow of electric charge. In most circuits, the charge carriers are electrons. The unit of electric current is the Ampere (A), which is defined as one Coulomb of charge flowing per second (1 A = 1 C/s). Remember that, conventionally, we define the direction of current as the direction in which positive charge would flow (opposite to the direction of electron flow).

Analogy: Think of electric current as the flow of water in a pipe. The more water that flows per second, the higher the current. 2.2 Potential Difference (Voltage) (V) Potential difference (voltage) is the electrical potential energy difference between two points in a circuit. It is the energy required to move one Coulomb of charge from one point to another. The unit of potential difference is the Volt (V), which is defined as one Joule of energy per Coulomb of charge (1 V = 1 J/C). A battery provides the potential difference that drives the current around the circuit.

Analogy: Voltage is like the pressure in a water pipe that forces the water to flow. Higher pressure (voltage) means a stronger push on the water (electrons), resulting in more flow (current). 2.3 Resistance (R) Resistance is the opposition to the flow of electric current. The unit of resistance is the Ohm (Ω). Materials with high resistance impede the flow of current more than materials with low resistance. Resistors are components specifically designed to provide resistance in a circuit.

Analogy: Resistance is like a narrow section in a water pipe that restricts the flow of water. The narrower the section (higher resistance), the less water (current) can flow through. 2.4 Ohm's Law Ohm's Law states the relationship between voltage (V), current (I), and resistance (R): V = I * R This law is fundamental to understanding and analyzing electric circuits. It tells us that the voltage across a resistor is directly proportional to the current flowing through it, and the constant of proportionality is the resistance. 2.5 Factors Affecting Resistance The resistance of a wire depends on several factors: Length (L): Longer wires have higher resistance. Imagine a longer, narrower water pipe provides more resistance.

Cross-sectional Area (A): Thicker wires have lower resistance. A wider water pipe allows more flow with less resistance. Material (ρ): Different materials have different inherent resistances. This is known as resistivity (ρ). Copper is a good conductor (low resistivity), while rubber is a good insulator (high resistivity).

Temperature (T): For most conductors, resistance increases with temperature. The increased atomic vibrations impede the flow of electrons. The relationship is mathematically represented as: R = ρ * (L/A) 2.6 Series Circuits In a series circuit, components are connected one after the other along a single path for current flow.

Current: The current is the same at all points in a series circuit. Imagine the same amount of water has to flow through each section of the pipe.

Voltage: The total voltage supplied by the battery is divided among the resistors in the series. V total = V 1 + V 2 + V 3 + ...

Resistance: The total resistance of a series circuit is the sum of the individual resistances. R total = R 1 + R 2 + R 3 + ... 2.7 Parallel Circuits In a parallel circuit, components are connected along multiple paths for current flow.

Current: The total current supplied by the battery is divided among the different branches of the parallel circuit. I total = I 1 + I 2 + I 3 + ...

Voltage: The voltage is the same across all branches in a parallel circuit. Imagine each section of the pipe experiencing the full water pressure.

Resistance: The reciprocal of the total resistance is equal to the sum of the reciprocals of the individual resistances. 1/R total = 1/R 1 + 1/R 2 + 1/R 3 + ...

For only two resistors in parallel: R total = (R 1 * R 2 ) / (R 1 + R 2 ) 2.8 Circuit Diagrams We use standard symbols to represent components in circuit diagrams: Resistor: ▬▬▬ Battery: ╵ ╵ (Longer line is the positive terminal)

Ammeter: Ⓔ Voltmeter: Ⓥ Switch: ▬/ ▬ (Open switch: circuit is broken; closed switch: circuit is complete)

Bulb: Ⓧ

Worked example

Example 1: Applying Ohm's Law

A cellphone charger with a resistance of 20 Ω is connected to a 220 V power supply. Calculate the current flowing through the charger.

Solution:

Given: R = 20 Ω, V = 220 V

Ohm's Law: V = I R

Rearrange to solve for I: I = V / R

Substitute values: I = 220 V / 20 Ω

Calculate: I = 11 A

Therefore, the current flowing through the cellphone charger is 11 A.