A-LevelPhysicsD.C. circuitsFeb/Mar 2018Paper 4 Q87 Marks
(a) Two properties of an ideal operational amplifier (op-amp) are infinite bandwidth and infinite slew rate. Explain what is meant by (i) infinite bandwidth, (ii) infinite slew rate. (b) An ideal op-amp is incorporated into the circuit of [Figure 8.1]. (i) Determine the resistance R_T of the thermistor T at which the output potential difference V_OUT is zero. (ii) The temperature of the thermistor is gradually increased so that its resistance decreases from 1.5R_T to 0.5R_T. On [Figure 8.2], draw a line to show the variation of the output potential difference V_OUT with the thermistor resistance. (iii) On [Figure 8.1], draw the symbol for a light-emitting diode (LED), connected at the output of the circuit, such that it emits light when the resistance of the thermistor is less than R_T.
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