(a)[4]
Explain, using band theory, why the resistance of an intrinsic semiconductor material falls as its temperature increases.
(b(i))[4]
Determine the temperature at which the light-emitting diode (LED) in Fig. 10.2 changes state, switching on or switching off.
(b(ii))[3]
State and explain whether the thermistor’s temperature is above or below the temperature calculated in (i) if the LED is to emit light.
(i)[4]
Determine the temperature at which the light-emitting diode (LED) in Fig. 10.2 changes from one state to the other, and give your answer in $^{\circ}\text{C}$.
(ii)[3]
State and explain whether the thermistor’s temperature is above or below the value found in (i) for the LED to emit light.