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General SciencePhysics: Electricity

In a series circuit containing three resistors of 10 ohms, 20 ohms, and 30 ohms, if the supply voltage is 120 V, calculate the total current flowing through the circuit.

2 A

6 A

12 A

0.5 A

Correct Answer

⚙️ TE • Technical Concept & PrincipleGeneral SciencePhysics: Electricity

Option A

2 A

Quick Summary:

In a series circuit, the total resistance is the sum of individual resistances. According to Ohm's law, the current flowing through a circuit is equal to the ratio of the supply voltage to the total equivalent resistance.

🔬SCScience SolutionConcept & Principle

💡 Explanation

💡 Everyday Analogy (Real-World Intuition)

Think of resistors as narrow pipes in a single path; adding more pipes in a line makes it harder for water to flow, just as adding resistors in series increases total opposition to electrical current.

🔢 Key Formulas

$R_{eq} = R_1 + R_2 + R_3$ — Formula for total resistance in a series circuit

$I = \frac{V}{R_{eq}}$ — Ohm's Law for calculating current

⚙️ Working Principle

The principle of conservation of energy and charge leads to Ohm's Law, defined as $V = I \times R_{eq}$ . For resistors connected in series, the path for charge flow is single, meaning the effective resistance is calculated as $R_{eq} = R_1 + R_2 + R_3$ . Once $R_{eq}$ is determined, the current $I$ is obtained by rearranging the formula to $I = \frac{V}{R_{eq}}$ .

📌 Key Points

▸
In series circuits, the current $I$ remains constant through every component.
▸
The total resistance $R_{eq}$ in series is always greater than the largest individual resistor.
▸
Voltage $V$ is distributed across each resistor proportional to its resistance.

✅ Advantages

▸
Simple wiring and design structure.
▸
Ease of installing a single switch to control all components.

❌ Disadvantages / Limitations

▸
If one component fails, the entire circuit is broken.
▸
Total resistance increases with each additional component, reducing overall current flow.

🛠️ Applications / Uses

▸
Decorative string lights (old-fashioned models).
▸
Fuses and circuit breakers used for protection.

📄 Additional Information

▸
Calculation: $R_{eq} = 10 \, \Omega + 20 \, \Omega + 30 \, \Omega = 60 \, \Omega$ . Then, $I = \frac{120 \, \text{V}}{60 \, \Omega} = 2 \, \text{A}$ .
▸
Option B (6 A) is incorrect as it results from dividing by a smaller wrong resistance; Option C (12 A) is a result of calculation error; Option D (0.5 A) results from dividing resistance by voltage ( $R/V$ ).

📊 Diagram / Illustration

✅

A is correct — The total resistance is 60 ohms, and dividing the 120 V supply by 60 ohms results in a total current of 2 A.

Core Concepts Used

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Ohm's Law Series Circuit Resistance Electrical Current

💡 EXAM TIP

Always verify if the circuit is series or parallel first; in series, current is constant, but in parallel, voltage is constant across components.

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