DC Circuits: Voltage, Current and Resistance

Electrical Engineering · CHAPTER 1 / 5

Level: introductory undergraduate · Study session: 15–20 minutes including practice.

Learning outcome: Calculate current and resistor dissipation in an ideal DC circuit.

Before you begin: Basic algebra, SI units and a willingness to sketch the problem.

1. Understand the idea

Voltage is electrical potential difference; current is charge flow rate. For an ohmic resistor at approximately constant temperature, current is proportional to voltage. A source supplies energy while the resistor converts it into heat. Check both resistance and power rating before choosing a component.

2. Write the model

V = IR; P = VI = V²/R

Define the symbols from the worked case before substituting values. Keep units consistent, record the assumptions and round only after the calculation.

3. Follow a worked example

With a 12 V supply and a 100 Ω resistor, current is 0.12 A and dissipation is 1.44 W. A 0.25 W resistor is unsuitable for this ideal steady operating point.

4. Explore the model

Figure: calculated teaching cases; straight segments connect sampled points, not experimental observations. Read exact values below.

Illustrative scenario sweep — synthetic educational data
Resistance (Ω)	Current at 12 V (A)	Power (W)
50	0.24	2.88
100	0.12	1.44
200	0.06	0.72

Sweep resistance with voltage fixed. Doubling resistance halves both current and resistor power.

5. Reproduce it yourself

Copy the input cases into Excel or a notebook and name each quantity and unit.
Recalculate each result from the stated equation or rule. For qualitative cases, explain the state or partition decision instead.
Change one input, predict the direction of change, then calculate again.
Write one sentence explaining where the model stops being valid.

6. Check your understanding

What current flows through 200 Ω at 10 V?

Reveal the answer and check your work

0.05 A or 50 mA.

Compare your result, units and reasoning. If they differ, return to the equation and test the worked case first.

7. Common mistake

Use low-voltage virtual examples; never practise on mains circuits.

Further study and academic note

Explore the discipline reference and further learning resources. This is an original IIMEEE introductory teaching note with synthetic examples; it is not a peer-reviewed research result or a professional design specification. Figures were constructed from the listed teaching cases. Resource links support further study and do not imply endorsement.