Ohm’s Law is one of the most important rules in electronics. Knowing the formula is not enough—you must practice solving problems to truly understand how voltage, current, and resistance work together.

This post walks you through common Ohm’s Law problems, solved step by step, with clear explanations.

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🔑 Ohm’s Law Recap

Ohm’s Law states:$$V = I \times R$$V=I×R

Where:

• V = Voltage (Volts)
• I = Current (Amps)
• R = Resistance (Ohms)

From this:

• $I = \frac{V}{R}$​
• $R = \frac{V}{I}$​

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🧠 Problem-Solving Strategy

1. Write down what is given
2. Identify what you need to find
3. Choose the correct formula
4. Substitute values
5. Solve carefully with correct units

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🔢 Problem 1: Find Current

Given:

• Voltage = 9V
• Resistance = 300Ω

Find: Current

Solution:

$$I = \frac{V}{R} = \frac{9}{300} = 0.03A$$I=RV​=3009​=0.03A

Answer:
✅ Current = 30mA

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🔢 Problem 2: Find Voltage

Given:

• Current = 0.5A
• Resistance = 10Ω

Find: Voltage

Solution:

$$V = I \times R = 0.5 \times 10 = 5V$$V=I×R=0.5×10=5V

Answer:
✅ Voltage = 5V

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🔢 Problem 3: Find Resistance

Given:

• Voltage = 12V
• Current = 0.2A

Find: Resistance

Solution:

$$R = \frac{V}{I} = \frac{12}{0.2} = 60Ω$$R=IV​=0.212​=60Ω

Answer:
✅ Resistance = 60Ω

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🔦 Problem 4: LED Circuit (Real-World Example)

Given:

• Supply voltage = 9V
• LED voltage drop = 2V
• Desired current = 20mA (0.02A)

Find: Resistor value

Solution:

Voltage across resistor:$$V_R = 9 – 2 = 7V$$VR​=9−2=7V

Resistor value:$$R = \frac{7}{0.02} = 350Ω$$R=0.027​=350Ω

Answer:
✅ Use 330Ω or 360Ω standard resistor

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🔥 Problem 5: Power Calculation

Given:

• Voltage = 10V
• Resistance = 50Ω

Step 1: Find Current

$$I = \frac{10}{50} = 0.2A$$I=5010​=0.2A

Step 2: Find Power

$$P = V \times I = 10 \times 0.2 = 2W$$P=V×I=10×0.2=2W

Answer:
✅ Use a ≥2W resistor

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🔌 Problem 6: USB Charger Example

Given:

• Voltage = 5V
• Power = 10W

Find: Current

Solution:

$$I = \frac{P}{V} = \frac{10}{5} = 2A$$I=VP​=510​=2A

Answer:
✅ Current = 2A

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🧮 Problem 7: Series Circuit

Given:

• R₁ = 100Ω
• R₂ = 200Ω
• Voltage = 12V

Step 1: Total Resistance

$$R_T = 100 + 200 = 300Ω$$RT​=100+200=300Ω

Step 2: Current

$$I = \frac{12}{300} = 0.04A$$I=30012​=0.04A

Answer:
✅ Current = 40mA

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🧪 Problem 8: Parallel Circuit (Basic)

Given:

• R₁ = 100Ω
• R₂ = 100Ω
• Voltage = 10V

Step 1: Total Resistance

$$R_T = 50Ω$$RT​=50Ω

Step 2: Current

$$I = \frac{10}{50} = 0.2A$$I=5010​=0.2A

Answer:
✅ Total current = 200mA

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⚠️ Common Beginner Mistakes

• Forgetting unit conversions (mA → A)
• Mixing up formulas
• Ignoring voltage drops
• Not checking power ratings
• Rounding too early

Always keep units clear.

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🌟 Why Practice Ohm’s Law Problems?

Solving problems helps you:

• Understand real circuits
• Choose correct components
• Avoid overheating and damage
• Build confidence in electronics

Practice turns theory into skill.

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🏁 Conclusion

Ohm’s Law is the foundation of electronics problem-solving. By practicing these problems, you build the ability to analyze and design safe and effective circuits.

At ElectroThink, we believe strong fundamentals create great engineers.