1. When the bridge is balanced V_B = V_C. Therefore, V_AB = V_AC and V_BD = V_CD

Using Kirchoff's voltage law and Ohm's law, prove that, at balance, (I5 = 0),

2. Suppose R4 is an unknown resistance and the bridge is balanced. Express R4 in terms of the other resistance values.

Now calculate R4 if R1 = 1000 ? , R2 = 500 ? and R3 = 3000 ?.

3. If ?R4 is the uncertainty in R4, write down an expression for ?R4 in terms of R1, R2 and R and their uncertainties, i.e. ?R , ?R and ?R.

4. Show that if R1 and R2 have no uncertainty - or the uncertainty is negligible compared to that of R3 and R4 - then :

Therefore, show that if R4 = 10 k? and R3 = 1 k? then ?R4 = 10?R3.

5. A transducer is a device which converts one quantity into another that is more readily measured. For example, the loudspeaker is a transducer which converts electrical signals into pressure waves or sound. In today's experiment, the thermistor is to be used as a transducer to change a temperature variation into a current variation. What is a thermistor?

6. Does the resistance of a thermistor vary linearly or non-linearly with temperature?

7. A reasonable estimate for the resistance of a thermistor - similar to that used in the thermistor experiment - at room temperature is 600 ? - 1 k?. If this thermistor forms the fourth arm of a Wheatstone bridge with R1 = R2 = 1000 ?, calculate the value of R3 that is required to balance the bridge at room temperature (20 °C).

8. If the current flowing through a thermistor was to change, would the resistance of the thermistor alter? Why?