An I-V characteristic shows how current varies with PD for a component

• An I-V characteristicA graph of currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). against potential differenceThe energyThe capacity to do work. Measured in joules (J). transferred per unit chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). between two points. Measured in volts (V). for a component, showing how the component behaves electrically. shows how currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). varies with PD for a component.
• Plotted with V on the x-axis and I on the y-axis (usually).
• Use a potential dividerA circuit that uses two or more resistors in series to produce a fraction of the source voltageThe energyThe capacity to do work. Measured in joules (J). transferred per unit charge between two points. Measured in volts (V). Informal term for potential difference. across one of the resistors. circuit to vary PD smoothly from zero.
• At any point on the curve, $R = V/I$ at that point.

Ohmic Conductor (Fixed Resistor)

• Straight line through the origin.
• CurrentThe rate of flow of charge. Measured in amperes (A). is directly proportional to PD.
• ResistanceThe opposition to current flow. The ratio of potential difference to current. Measured in ohms (Ω). is constant. $R = 1/gradient$ of the I-V graph.

Filament Lamp

• Curve: gradient decreases as V increases.
• ResistanceThe opposition to current flow. The ratio of potential difference to current. Measured in ohms (Ω). increases because the filament heats up.
• Hotter filament means more ion vibrations, more collisions with electrons.
• The graph is symmetrical about the origin.

Diode / LED

• Current flows in one direction only (the forward direction).
• A threshold voltageThe energyThe capacity to do work. Measured in joules (J). transferred per unit charge between two points. Measured in volts (V). Informal term for potential difference. (~0.6 V for silicon) must be exceeded before current flows.
• In reverse bias, effectively zero current flows.
• ResistanceThe opposition to current flow. The ratio of potential difference to current. Measured in ohms (Ω). is very high below threshold, very low above it.

NTC Thermistor

• Gradient increases as V increases.
• Resistance decreases because increased current heats the thermistorA component whose resistance decreases significantly as temperature increases (negative temperature coefficient)..
• Heating increases the number densityMass per unit volume of a material. Measured in kg m⁻³.The number of charge carriers per unit volume in a material. Measured in m⁻³. of charge carriers in the semiconductor.