u00d7 10 5 gt gt 15v with 15 volts applied to the base electrode the first transistor 54 will turn on causing a current to flow through the first light emitting diode 60 this causes the first light emitting diode 60 to light indicating that there is no continuity between the first and second measurement points since the first transistor 54 is conducting the voltage at the anode of the first light emitting diode 60 is less than 2 volts consequently the voltage appearing at the base electrode of the second transistor 70 is less than the required turn on voltage if there is electrical continuity for example one ohm or less between the first and second measurement points the current flowing through the first resistor 22 is approximately equal to 5 volts u00f7 1 u00d7 10 6 ohm 1 ohm which is approximately equal to 5 u00d7 10 6 amp consequently the voltage which appears across the first and second measurement terminals 12 and 20 is approximately equal to 5 u00d7 10 6 volts 5 u00d7 10 6 a u00d7 1 u03c9 5 u00d7 10 6 v consequently the voltage appearing across the inverting and non inverting inputs of the operational amplifier 36 will be approximately equal to 5 u00d7 10 6 volts since the gain of the operational amplifier is 1 u00d7 10 5 the voltage appearing at the output of the operational amplifier 36 is equal to 5 u00d7 10 6 v u00d7 1 u00d7 10 5 which is equal to 0 5 volt since 0 5 volt is less than the base voltage required to turn on the first transistor 54 the first light emitting diode 60 will turn off since the first transistor.