In this experiment you will investigate a thermistor. You are provided with: • a battery of cells • a switch or plug key • a fixed resistor • a thermistor • a voltmeter • a thermometer • connecting leads • a beaker containing ice and water. The supervisor has assembled the apparatus shown in Fig. 2.1.[Figure 2.1]

1. (a)Draw a circuit diagram of the circuit.[3]
2. (b)There is a thermometer attached to your bench by a small amount of adhesive putty. Record the temperature TW on the thermometer. This is room temperature. Close the switch. Record the reading VW on the voltmeter Open the switch. TW = ...................................... °C VW = ...................................... V[1]
3. (c)There is a beaker containing ice and water near the thermistor. Carefully move the beaker closer to the circuit and submerge the thermistor in the cold water in the beaker. Wait about one minute until the reading on the voltmeter is steady. Record the new voltage VC. Remove the thermistor from the cold water. VC = ...................................... V[1]
4. (d)(i)Assume that the temperature TC of the ice and water is 0°C. Calculate the average change in voltage for one degree temperature change ΔVAV using the equation: ΔVAV = (VC – VW) (TW – TC) State the unit of your answer. ΔVAV = ...................................... unit ......................................[2]
5. (d)(ii)Use your answer to (d)(i) to predict the voltage VPB across the thermistor when the thermistor is at body temperature. Body temperature is 37°C. You may assume that the average change in voltage for one degree temperature change ΔVAV is constant. VPB = ...................................... V[1]
6. (d)(iii)A student suggests that if the thermistor is held between a thumb and forefinger for two minutes, the reading on the voltmeter will be the same as the predicted voltage VPB in (d)(ii). Two quantities are considered to be equal, within the limits of experimental accuracy, if their values are within 10% of each other. Hold the thermistor between your thumb and forefinger for two minutes, until the voltmeter shows a new steady reading. Read and record this voltage VAB. State whether the student's results indicate that VPB and VAB are equal within the limits of experimental accuracy. Support your statement with a calculation. VAB = ...................................... V calculation statement[2]

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