Filament lamp
The I/V graph for a filament lamp is curved. It starts steep but gets shallower as the voltage rises. This is because it gets hot due to being a coiled up length of wire. Current flowing through the lamp increases its temperature, and the resistance of a metal increases as the temerature increases.
Thermistor
A thermistor is a resistor with a resistance that depends on its temperature. For example, for a particular thermistor, as the temperature rises its resistance may also rise.
Warming the thermistor gives more electrons enough energy to escape fom their atoms. Therefore there are more charge carriers available, so the resistance is lower.
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