Physics - Term 3 - Week 5

An electric circuit is a closed loop that allows current to flow. It consists of a power source, conductors, and loads. The fundamental principle governing electric circuits is Ohm's Law, which states that the current (I) 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.

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 (R_total = R1 + R2 + ... + Rn). In contrast, in a parallel circuit, components are connected across the same voltage source, and the total current is the sum of the currents through each component. The total resistance in a parallel circuit can be calculated using the formula 1/R_total = 1/R1 + 1/R2 + ... + 1/Rn.

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

Suppose we have three resistors in series: R1 = 2Ω, R2 = 3Ω, and R3 = 5Ω. The total resistance is calculated as R_total = R1 + R2 + R3 = 2Ω + 3Ω + 5Ω = 10Ω. Therefore, the total resistance of the series circuit is 10 ohms.

Let's work together on a parallel circuit problem. We have two resistors, R1 = 6Ω and R2 = 3Ω. To find the total resistance, we use the formula 1/R_total = 1/R1 + 1/R2. Substituting the values, we get 1/R_total = 1/6 + 1/3. Finding a common denominator, we have 1/R_total = 1/6 + 2/6 = 3/6. Thus, R_total = 6/3 = 2Ω. The total resistance of the parallel circuit is 2 ohms.

Now, try these problems on your own. 1) Calculate the current in a circuit with a voltage of 24V and a resistance of 8Ω. 2) Find the total resistance of three resistors in series: R1 = 4Ω, R2 = 5Ω, R3 = 6Ω. 3) Determine the total resistance of two resistors in parallel: R1 = 12Ω and R2 = 4Ω.

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

Answer: V = I × R

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

• The sum of individual resistances
• The product of individual resistances
• The average of individual resistances
• None of the above

Answer: The sum of individual resistances

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

• It decreases
• It increases
• It remains the same
• It depends on the voltage

Answer: It increases

In a parallel circuit, the total current is the sum of the currents through each branch, which increases the total current.

Answer: 2A

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

Answer: 10Ω

The total resistance in series is R_total = R1 + R2 = 3Ω + 7Ω = 10Ω.

• Current is the same through all components
• Voltage is the same across all components
• Resistance is the same across all components
• None of the above

Answer: Voltage is the same across all components

In a parallel circuit, all components share the same voltage from the power source.

Answer: 3Ω

Using the formula 1/R_total = 1/R1 + 1/R2, we find 1/R_total = 1/4 + 1/12 = 3/12, so R_total = 12/3 = 4Ω.