Physics - Term 4 - Week 3

An electric circuit is a closed loop that allows current to flow from a power source through various components and back to the source. The basic components of a circuit include a power source (like a battery), conductors (wires), and loads (like resistors or light bulbs). Understanding how these components interact is crucial for analyzing circuit behavior.

Ohm's Law states that the current (I) flowing through a conductor between two points is directly proportional to the voltage (V) across the two points and inversely proportional to the resistance (R) of the conductor. This relationship can be expressed with the formula: V = I × R. This law is fundamental in calculating how much current will flow in a circuit given a specific voltage and resistance.

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 the individual resistances. In contrast, a parallel circuit has components connected across the same voltage source, allowing multiple paths for current to flow. The total resistance in a parallel circuit can be calculated using the formula: 1/R_total = 1/R1 + 1/R2 + ... + 1/Rn.

Suppose we have a circuit with a voltage of 12 volts and a resistance of 4 ohms. To find the current, we use Ohm's Law: I = V/R. Therefore, I = 12V / 4Ω = 3A. This means that a current of 3 amperes flows through the circuit.

Consider a series circuit with three resistors: R1 = 2Ω, R2 = 3Ω, and R3 = 5Ω. The total resistance (R_total) is calculated as R_total = R1 + R2 + R3 = 2Ω + 3Ω + 5Ω = 10Ω.

For a parallel circuit with two resistors, R1 = 6Ω and R2 = 3Ω, the total resistance can be calculated as follows: 1/R_total = 1/R1 + 1/R2 = 1/6 + 1/3 = 1/6 + 2/6 = 3/6. Therefore, R_total = 6/3 = 2Ω.

Let's work together on a problem. If a circuit has a voltage of 24 volts and a resistance of 8 ohms, what is the current? Use Ohm's Law to find the answer. Students should calculate I = V/R = 24V / 8Ω = 3A.

Now, consider a series circuit with two resistors: R1 = 4Ω and R2 = 6Ω. What is the total resistance? Students should add the resistances: R_total = R1 + R2 = 4Ω + 6Ω = 10Ω.

For a parallel circuit with R1 = 12Ω and R2 = 4Ω, calculate the total resistance. Students should use the formula: 1/R_total = 1/R1 + 1/R2 = 1/12 + 1/4 = 1/12 + 3/12 = 4/12, leading to R_total = 12/4 = 3Ω.

Students will solve the following problems on their own: 1) A circuit has a voltage of 30V and a resistance of 10Ω. Calculate the current. 2) Find the total resistance of a series circuit with resistors of 5Ω, 10Ω, and 15Ω. 3) Calculate the total resistance of a parallel circuit with resistors of 8Ω and 4Ω.

As a challenge, students can calculate the total resistance of a circuit with three resistors in parallel: R1 = 6Ω, R2 = 3Ω, and R3 = 2Ω. They should apply the parallel resistance formula and verify their results with peers.

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

Answer: V = I × R

Ohm's Law states that voltage is equal to current multiplied by resistance.

• R_total = R1 + R2 + R3
• R_total = 1/R1 + 1/R2
• R_total = R1 × R2
• R_total = R1 - R2

Answer: R_total = R1 + R2 + R3

In a series circuit, the total resistance is the sum of all individual resistances.

• It increases
• It decreases
• It stays the same
• It doubles

Answer: It decreases

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

Answer: 4A

Using Ohm's Law, I = V/R = 48V / 12Ω = 4A.

Answer: 15Ω

R_total = R1 + R2 + R3 = 3Ω + 5Ω + 7Ω = 15Ω.

• Current is the same through all components
• Voltage is the same across all components
• Total resistance is the sum of individual resistances
• All components must have the same resistance

Answer: Voltage is the same across all components

In a parallel circuit, the voltage across each component is the same.

• 2Ω
• 4Ω
• 8Ω
• 16Ω

Answer: 2Ω

Using the formula for parallel resistors: 1/R_total = 1/R1 + 1/R2 = 1/4 + 1/4 = 1/2, so R_total = 2Ω.