Q.12
A battery delivers a steady current of 1.25 A for 90 minutes.
The total charge ‘Q’ (in Coulomb units) is:
Battery Charge Calculation: 1.25A 90 Minutes = 6750C
The correct answer is 6750 coulombs.
Formula & Calculation
Charge Q = I × t, where current I = 1.25 A and time must be in seconds.
Step 1: Convert 90 minutes = 90 × 60 = 5400 seconds
Step 2: 1.25 × 5400 = 6750 coulombs
Units check: ampere-seconds = coulombs ✓
Option Analysis
| Option | Calculation Attempt | Error Type |
|---|---|---|
| 6750 | 1.25 × 5400 |
Correct |
| 1012.5 | Minutes × 11.25? | Time unit error |
| 112.5 | 1.25 × 90 |
Minutes used directly |
| 12.5 | 1.25 × 10 |
Gross miscalculation |
Exam Formula Card
Q = I × t (Charge = Current × Time) t in seconds! 1 min = 60 s 1.25 × (90×60) = 6750 C ✓
Common Trap Exposed
Pro Tip: Always convert minutes to seconds first—
90 × 60 = 5400is the #1 mistake in these problems.
GATE Physics Strategy
- Memorize:
1 minute = 60 seconds - Check units: Amps × Seconds = Coulombs
- Spot distractors: 112.5 uses raw minutes
- Practice mental math: 1.25 × 5400 = (1 × 5400) + (0.25 × 5400)
