Orientation
Lesson goal: define current as rate of charge flow and distinguish conventional current from electron flow.
The critical language repair is that current flows; voltage does not.
Core Content
Current is the rate at which charge passes a point:
$$I = \frac{Q}{t}$$
Conventional current is defined as the direction positive charge would move in the external circuit. Electron flow is opposite to conventional current in a metal wire.
| Quantity | Symbol | Unit | Meaning |
|---|---|---|---|
| current | $I$ | A | charge per second |
| charge | $Q$ | C | amount of electric charge |
| time | $t$ | s | duration of flow |
Concept Check
-
Current is measured in:
- A. volts
- B. amps
- C. ohms
- D. joules
Answer: B.
-
Conventional current in an external circuit is from:
- A. negative to positive
- B. positive to negative
- C. north to south
- D. high resistance to low resistance only
Answer: B.
-
If
20 Cpasses a point in8 s, current is:- A.
2.5 A - B.
12 A - C.
160 A - D.
0.40 A
Answer: A.
- A.
Applied Practice
A current of $2.5\ \text{A}$ flows for $8.0\ \text{s}$. Calculate the charge that passes a point.
$$Q = It = 2.5\times8.0 = 20\ \text{C}$$
Final answer: $20\ \text{C}$.
Deep Practice And Writing
Prompt: explain why current is not "used up" by a resistor in a simple series circuit.
Maintenance Loop
Retrieve $I = Q/t$, conventional current direction, and electron-flow direction.