Physics - Term 3 - Week 10

An electric circuit is a closed loop that allows current to flow. It consists of a power source, conductors, and loads. The flow of electric charge is driven by voltage, and the relationship between voltage (V), current (I), and resistance (R) is defined by Ohm's Law: V = I × R. Understanding this relationship is crucial for analyzing circuits.

In a series circuit, components are connected end-to-end, so the same current flows through each component. The total resistance in a series circuit is the sum of individual resistances: R_total = R1 + R2 + ... + Rn. In contrast, a parallel circuit has components connected across the same voltage source, allowing multiple paths for current. The total resistance in a parallel circuit can be calculated using the formula: 1/R_total = 1/R1 + 1/R2 + ... + 1/Rn.

Consider a series circuit with three resistors: R1 = 4Ω, R2 = 6Ω, and R3 = 10Ω. To find the total resistance, we add the resistances: R_total = R1 + R2 + R3 = 4Ω + 6Ω + 10Ω = 20Ω. If the circuit is powered by a 12V battery, we can find the current using Ohm's Law: I = V/R_total = 12V/20Ω = 0.6A.

For a parallel circuit with two resistors, R1 = 3Ω and R2 = 6Ω, we calculate the total resistance using the formula: 1/R_total = 1/R1 + 1/R2 = 1/3 + 1/6. Finding a common denominator gives us: 1/R_total = 2/6 + 1/6 = 3/6, so R_total = 2Ω. If connected to a 12V battery, the current through each resistor can be calculated using Ohm's Law.

Let's work through a problem together. A series circuit has two resistors, R1 = 5Ω and R2 = 15Ω. What is the total resistance? Students should calculate R_total = R1 + R2. After calculating, discuss how the current would change if the voltage source is increased to 30V.

Now, consider a parallel circuit with three resistors: R1 = 4Ω, R2 = 12Ω, and R3 = 24Ω. Calculate the total resistance. Students should apply the parallel resistance formula and then discuss how the current through each resistor would differ if the voltage is 24V.

Students will complete a worksheet with problems involving both series and parallel circuits. For example, calculate the total resistance for a series circuit with R1 = 10Ω, R2 = 20Ω, and R3 = 30Ω. Then, calculate the total resistance for a parallel circuit with R1 = 5Ω, R2 = 10Ω, and R3 = 15Ω. Students should also find the current for each circuit if connected to a 12V battery.

• V = I + R
• V = I × R
• V = I / R
• V = R / I

Answer: V = I × R

Ohm's Law states that voltage (V) is equal to the current (I) multiplied by the resistance (R).

• The sum of the individual resistances
• The product of the individual resistances
• The average of the individual resistances
• Always less than the smallest resistor

Answer: The sum of the individual resistances

In a series circuit, the total resistance is calculated by adding all individual resistances together.

Answer: 10Ω

Total resistance in series is R_total = R1 + R2 + R3 = 2Ω + 3Ω + 5Ω = 10Ω.

• It increases
• It decreases
• It remains the same
• It doubles

Answer: It decreases

Adding more resistors in parallel provides additional paths for current, which decreases the total resistance.

Answer: 3A

Using Ohm's Law, I = V/R = 12V/4Ω = 3A.

• 2Ω
• 4Ω
• 1.5Ω
• 9Ω

Answer: 2Ω

Using the formula for parallel resistors: 1/R_total = 1/R1 + 1/R2 = 1/6 + 1/3 = 1/2, thus R_total = 2Ω.

Answer: In series circuits, current flows through each component sequentially, while in parallel circuits, components are connected across the same voltage source, allowing multiple paths for current.