Overview
This lecture explains the concept of electric charge, its formula, units, and demonstrates solving basic charge calculation problems.
What is Electric Charge?
- Charge (Q) measures the total current that flows over a period of time.
- It's analogous to the total water flow down a river over time in the water analogy.
- Charge is represented by the letter Q and measured in coulombs (C).
Charge Calculation Formula
- The main equation: Q = I × t
- Q = charge (coulombs)
- I = current (amperes/amps)
- t = time (seconds)
- Rearranged to find current: I = Q ÷ t
Example Problems
- If a kettle draws 12 A for 50 s: Q = 12 × 50 = 600 C.
- If a phone charger transfers 43.2 kC in 2 hours:
- Convert 43.2 kC to C: 43.2 × 1000 = 43,200 C.
- Convert 2 hours to seconds: 2 × 60 × 60 = 7,200 s.
- Current: I = 43,200 ÷ 7,200 = 6 A.
Key Terms & Definitions
- Charge (Q) — Total amount of electricity transferred, measured in coulombs (C).
- Current (I) — Rate of flow of charge, measured in amperes (A).
- Time (t) — Duration over which current flows, measured in seconds (s).
- Coulomb (C) — The SI unit for electric charge.
Action Items / Next Steps
- Practice converting units (kilo-coulombs to coulombs, hours to seconds).
- Solve sample problems using Q = I × t and I = Q ÷ t.