Physics - Term 4 - Week 9

Electric circuits consist of several key components: a power source (like a battery), conductors (wires), and loads (like resistors or light bulbs). The power source provides the electrical energy, while the conductors allow the flow of electric current. Loads convert electrical energy into other forms of energy, such as light or heat. Understanding these components is crucial for analyzing how circuits function.

Ohm's Law is a fundamental principle in electronics that relates voltage (V), current (I), and resistance (R) in a circuit. It is expressed as V = I × R. This means that the voltage across a conductor is directly proportional to the current flowing through it, provided the temperature remains constant. This law allows us to calculate any one of the three variables if the other two are known.

Circuits can be arranged in two main configurations: series and parallel. In a series circuit, components are connected end-to-end, so the same current flows through all components. This configuration results in a total resistance that is the sum of individual resistances. In contrast, parallel circuits have components connected across the same voltage source, allowing multiple paths for current. The total resistance in a parallel circuit is less than the smallest individual resistance.

Consider a circuit with a voltage of 12 volts and a resistance of 4 ohms. To find the current, we can use Ohm's Law: I = V / R. Substituting the values, we get I = 12V / 4Ω = 3A. Therefore, the current flowing through the circuit is 3 amperes.

If we have three resistors in series with values of 2Ω, 3Ω, and 5Ω, the total resistance (R_total) can be calculated as R_total = R1 + R2 + R3. Thus, R_total = 2Ω + 3Ω + 5Ω = 10Ω. This total resistance affects the current flowing through the circuit.

For resistors in parallel, the total resistance can be calculated using the formula 1/R_total = 1/R1 + 1/R2 + 1/R3. If we have two resistors of 4Ω and 6Ω, we find R_total as follows: 1/R_total = 1/4 + 1/6. Finding a common denominator, we get 1/R_total = 3/12 + 2/12 = 5/12. Therefore, R_total = 12/5 = 2.4Ω.

Let's work together on a problem. A circuit has a voltage of 24 volts and a resistance of 8 ohms. What is the current? Using Ohm's Law, I = V / R, we substitute the values: I = 24V / 8Ω = 3A. Now, try calculating the current for a circuit with 30 volts and 10 ohms of resistance.

In a series circuit with two resistors of 5Ω and 10Ω, what is the total resistance? We add the resistances: R_total = 5Ω + 10Ω = 15Ω. Now, if we add a third resistor of 5Ω, what is the new total resistance? Guide the students to calculate R_total = 15Ω + 5Ω = 20Ω.

Consider a parallel circuit with two resistors of 12Ω and 4Ω. To find the total resistance, we use the formula 1/R_total = 1/12 + 1/4. Calculate the total resistance together, leading to R_total = 3Ω. Now, ask students to find the total resistance if a third resistor of 6Ω is added in parallel.

Solve the following problems independently: 1) A circuit has a voltage of 48 volts and a resistance of 12 ohms. Calculate the current. 2) If the current in a circuit is 2A and the resistance is 6Ω, what is the voltage? Show your calculations.

You have three resistors: 3Ω, 6Ω, and 9Ω connected in series. Calculate the total resistance. Then, if the circuit is powered by a 36V battery, find the current flowing through the circuit.

In a parallel circuit with resistors of 8Ω and 16Ω, calculate the total resistance. Then, if the voltage across the circuit is 24V, determine the current flowing through each resistor.

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

Answer: V = I × R

Ohm's Law states that voltage equals current multiplied by resistance.

• It is less
• It is equal
• It is more
• It varies

Answer: It is more

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

• It increases
• It decreases
• It stays the same
• It stops

Answer: It increases

Removing a resistor in parallel decreases total resistance, which increases current.

Answer: 4A

Using Ohm's Law, I = V / R = 60V / 15Ω = 4A.

Answer: 15Ω

In series, total resistance is R_total = R1 + R2 = 5Ω + 10Ω = 15Ω.

• 10V
• 7V
• 12V
• 15V

Answer: 10V

Using Ohm's Law, V = I × R = 5A × 2Ω = 10V.

• They share the same current
• They share the same voltage
• They have the same resistance
• They cannot be combined

Answer: They share the same voltage

In a parallel circuit, all components share the same voltage across them.