Physics - Term 2 - Week 10

An electric circuit is a closed loop that allows electric current to flow. 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 circuits. Ohm's Law, which states that V = IR (voltage = current x resistance), is fundamental in calculating the behavior of 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 + ...). In contrast, in a parallel circuit, components are connected across the same voltage source, and the total resistance can be calculated using the formula 1/R_total = 1/R1 + 1/R2 + ... This distinction is essential for understanding how circuits function.

Consider a series circuit with a 12V battery and two resistors: R1 = 4Ω and R2 = 6Ω. To find the total resistance, we add the resistances: R_total = R1 + R2 = 4Ω + 6Ω = 10Ω. Using Ohm's Law, we can find the current: I = V/R_total = 12V/10Ω = 1.2A. This current flows through both resistors.

Now, let's analyze a parallel circuit with the same resistors (R1 = 4Ω and R2 = 6Ω) connected to a 12V battery. The total resistance can be calculated as follows: 1/R_total = 1/R1 + 1/R2 = 1/4 + 1/6. Finding a common denominator (12), we get 1/R_total = 3/12 + 2/12 = 5/12, thus R_total = 12/5 = 2.4Ω. The total current can be calculated as I = V/R_total = 12V/2.4Ω = 5A.

Let's work through a problem together. A series circuit has a 9V battery and three resistors: R1 = 2Ω, R2 = 3Ω, and R3 = 4Ω. First, calculate the total resistance: R_total = R1 + R2 + R3. Next, find the current using Ohm's Law. After calculating, discuss how the voltage is distributed across each resistor.

Now, consider a parallel circuit with a 24V battery and two resistors: R1 = 8Ω and R2 = 12Ω. Calculate the total resistance using the parallel formula. Then, determine the current through each resistor. Discuss how the voltage across each resistor remains the same and how this affects the overall current in the circuit.

Complete the following problems on your own: 1) A series circuit with a 15V battery and resistors of 5Ω and 10Ω. Calculate the total resistance and current. 2) A parallel circuit with a 10V battery and resistors of 5Ω and 15Ω. Find the total resistance and the current through each resistor. Be prepared to share your solutions with the class.

• 10Ω
• 5Ω
• 8Ω
• 15Ω

Answer: 10Ω

In a series circuit, total resistance is the sum of individual resistances: 3Ω + 5Ω + 2Ω = 10Ω.

• Increases
• Decreases
• Remains the same
• Becomes infinite

Answer: Increases

In a parallel circuit, if one resistor fails, the total resistance increases because there are fewer paths for current to flow.

Answer: V = IR

Ohm's Law states that the voltage (V) across a conductor is directly proportional to the current (I) flowing through it, with resistance (R) as the constant of proportionality.

• 3A
• 12A
• 4A
• 6A

Answer: 3A

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

Answer: 2Ω

Using the formula 1/R_total = 1/R1 + 1/R2, we find 1/R_total = 1/6 + 1/3 = 1/2, so R_total = 2Ω.

• Equal
• Varies
• Zero
• Depends on the current

Answer: Varies

In a series circuit, the voltage across each resistor varies depending on its resistance.

Answer: Total current increases.

Adding more resistors in parallel provides additional paths for current, thus increasing the total current.