Lesson page
Lesson 12: Calculation Workflow for Written Exam Speed
Read the lesson, then answer the multiple-choice practice set below. You get instant right or wrong feedback with explanation.
Electrical Calculations Exam Practice
Lesson Content
Use this workflow until it becomes automatic. Under exam pressure, process beats memory.
Japanese Key Term
計算しなさい（けいさんしなさい / calculate）
Hiragana
けいさんしなさい
English Meaning
Calculate
Simple Explanation
This lesson gives you a strict sequence: identify data, write formula, convert units, solve, and verify reasonableness.
Detailed Explanation
Most students lose marks from avoidable mistakes, not difficult theory. Use a five-step routine every time. Step 1: mark known values and unknown target. Step 2: write only the relevant formula. Step 3: convert units before substitution. Step 4: calculate with units shown. Step 5: check whether the answer scale is realistic (for example, current should not be thousands of amps in a small home load question). This routine works across Ohm's Law, power, energy, and voltage-drop basics.
Key Vocabulary
- 計算しなさい（けいさんしなさい / calculate）
- 求めなさい（もとめなさい / find）
- 電力量（でんりょう / electrical energy）
- 単位換算（たんいかんさん / unit conversion）
Formula
I = V / R
P = V x I
Energy (Wh) = Power (W) x Time (h)
Worked Example
Question data: V = 100 V, R = 25 ohms. Target: I. Formula: I = V / R. Substitute: I = 100 / 25 = 4 A. Check: 4 A is plausible for this scale.
Exam Tips
If answers look close, unit conversion is usually the deciding factor. Verify W vs kW and mA vs A carefully.
Common Exam Trap
Students often compute correctly but choose the wrong option because they skip final unit conversion.
Site Reality in Japan
On site, calculation errors can lead to wrong breaker selection, conductor overheating, or nuisance tripping. Accuracy matters beyond the exam.
Practice Question
A 1.2 kW load runs for 3 hours. What is the energy in kWh and Wh?
Answer
3.6 kWh and 3600 Wh
Explanation
Energy = 1.2 x 3 = 3.6 kWh. Convert to Wh by multiplying by 1000: 3600 Wh.
1. A load uses 600 W for 2 hours. How much energy is used?
0.6 kW x 2 h = 1.2 kWh.
2. Which formula gives electric power in a DC circuit?
The base power formula is P = V x I.
3. Two 30 ohm resistors are in series. What is total resistance?
Series resistance adds directly.
4. Two 30 ohm resistors are in parallel. What is total resistance?
Equal parallel resistors halve the value.
5. A bad joint has 0.5 ohms resistance. If 10 A flows, power loss at the joint is:
P = I^2 R = 100 x 0.5 = 50 W.
6. What is the meaning of 力率?
力率 means power factor.