Sketch and explain the current‑voltage graphs for:
Use analogies, examples and exam tips to make the concepts clear.
⚡️ Ohm’s Law applies: \$V = IR\$.
The graph is a straight line through the origin.
| Voltage \$V\$ (V) | Current \$I\$ (A) |
|---|---|
| 0 | 0 |
| 5 | 1 |
| 10 | 2 |
🔌 Analogy: Think of the resistor as a pipe with a fixed width. The water flow (current) increases linearly with the pressure (voltage).
📌 Exam Tip: Show that the slope of the line equals the resistance \$R\$ and that the line passes through the origin.
💡 The filament’s resistance rises with temperature, so the \$V\$–\$I\$ curve is non‑linear and bends upwards.
Initially, at low voltage, the filament is cold and has low resistance – current rises quickly. As it heats, resistance increases, slowing the rise of current.
| Voltage \$V\$ (V) | Current \$I\$ (A) |
|---|---|
| 0 | 0 |
| 2 | 0.8 |
| 4 | 1.4 |
| 6 | 1.8 |
🔥 Analogy: Imagine a garden hose that gets thicker as it heats up; the water flow slows down even if you keep turning the tap.
📌 Exam Tip: Explain that the curve is concave upward and that the slope (d\$V\$/d\$I\$) increases with voltage due to rising resistance.
🔋 A diode conducts only after a threshold voltage (≈0.7 V for silicon). The \$V\$–\$I\$ graph shows almost zero current until this point, then an exponential rise.
Mathematically: \$I = Is(e^{V/(nVT)}-1)\$, where \$I_s\$ is the saturation current.
| Voltage \$V\$ (V) | Current \$I\$ (A) |
|---|---|
| 0.0 | 0 |
| 0.3 | 0.0001 |
| 0.6 | 0.001 |
| 0.7 | 0.01 |
| 1.0 | 0.1 |
🔌 Analogy: Think of a one‑way gate that stays closed until you push hard enough (threshold voltage), then it opens and lets a lot of people (current) through.
📌 Exam Tip: Identify the threshold voltage, describe the exponential rise, and note that the diode is a non‑linear element.