2 What is meant by 'negative temperature coefficient'? Select one of ... A) The voltage at A increases as temperature increases. B) The resistance decreases as temperature increases. C) The resistance decreases as temperature decreases. D) The reistance is not affected by changes of temperature.
3 If temperature increases, what happens to the voltage at point a? Select one of ... A) Nothing. B) It decreases. C) Depends on the setting of VR1. D) It increases.
4 A comparator is a circuit that: Select one of ... A) is used to compare one voltage with another. B) is used to compare a varying voltage with a fixed voltage. C) has a positive output when the (+) input is above 0 V. D) has high gain.
5 The function of VR1 is to: Select one of ... A) set the switch-on temperature. B) adjust the sensitivity of the circuit. C) compensate for the input offset voltage. D) limit the current through R1.
6 If the transistor is switching on at too high a temperature, what adjustment should be made? Select one of ... A) Replace R1 with a thermistor of higher resistance. B) Adjust VR1 to decrease its resistance. C) Adjust VR1 to increase its resistance. D) Replace Q1 with a MOSFET with higher threshold point.
7 What do we mean by the 'input offset voltage' of IC1? Select one of ... A) The output voltage when its inputs are equal. B) The output voltage when its inputs are 0 V. C) The input voltages when itsoutput is 0 V. D) The difference between input voltages that results in 0 V output.
8 The main disadvantage of a thermistor is that: Select one of ... A) it takes several minutes to respond to temperature changes. B) its resistance is not linearly related to temperature. C) it can not be used below 0° C. D) it is expensive.
9 Why does it not matter if R3 and R4 are not exactly equal? Select one of ... A) The current through R3 and R4 is very small. B) This is a low-precision circuit. C) The setting of VR1 can compensate for this. D) The gain of the amplifier is not exactly known.
10 The gate voltage of Q1 swings very sharply up or down at the set temperature because: Select one of ... A) the open loop gain of IC1 is very high. B) the voltage difference between points a and c is large. C) the resistance of R1 changes very rapidly as temperature changes. D) there is no resistor between IC1 and Q1..
