Mapping How Components Behave with Electricity
⚡ Mapping How Components Behave with Electricity
Every electrical component responds differently when you apply a voltage across it. A resistor at room temperature obediently follows Ohm's Law — double the voltage, double the current. But a filament lamp misbehaves: as it heats up, its resistance increases, so the current grows more slowly. And a diode is even more dramatic — it barely conducts at all in one direction, but conducts freely in the other.
To understand these behaviours, physicists draw I-V characteristic graphs. These plots put voltage (V) on the horizontal axis and current (I) on the vertical axis. The shape of the curve tells you everything about how the component behaves — whether its resistance stays constant, increases, or changes with direction.
This is a Required Practical in GCSE Physics. You build a circuit, vary the voltage using a variable resistor, and measure both current and voltage to plot the characteristic curve for each component.
Figure 1: Circuit for investigating I-V characteristics — ammeter in series, voltmeter in parallel
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The Shape-Story for Each Component
- Resistor = Straight (behaves predictably, like a well-behaved student — straight line)
- Filament lamp = S-curve (gets lazy as it heats up — curve flattens off)
- Diode = Hockey stick (flat then suddenly kicks up at 0.6 V)
Ammeter vs Voltmeter Placement
Remember: Ammeter is in Aeries (series) with an A — wait, try this: Voltmeter is in Varallel (parallel). Or better: the voltmeter "wraps around" the component like a hug (parallel), while the ammeter is "in the queue" (series).
Reading Resistance from I-V Graph
R = V/I — "V over I, not the slope, that's the lie!" The gradient shows 1/R, but R = V/I. Always read off a point, not the slope.
Quick Check: At a certain point on a filament lamp's I-V graph, the voltage is 6 V and the current is 0.2 A. Calculate the resistance of the lamp at this point.
R = V/I = 6/0.2 = 30 Ω. Note: this is calculated from the coordinates of the point (V/I), NOT from the gradient of the graph.
Now try it yourself
Quiz · Question 1 of 13
What does an I-V characteristic graph show for a component?
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This topic in real past papers
Every real exam question we've found on i-v characteristics, with a full worked answer.