Data Sheet

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42. Kirchhoff’s Voltage Law

Build the circuit shown on the left and you will see the

star LED (70) is on, but the lamp (76) is very dim and

the and the motor (95) does not spin or spins very slowly.

This is because the voltage across the lamp (76) and

motor (95) is small compared to the voltage across the

star LED (70). Kirchhoff’s voltage law states: The sum of

the voltages around a closed network is zero. If a drop in

voltage is considered as a negative voltage and a rise in

voltage a positive voltage, then the following equation is a

mathematical representation of Kirchhoff’s voltage law:

+ V

= 0

This shows that the voltage drop across the battery module

(91) must equal the voltage drop across the lamp (76)

plus the voltage drop across the star LED (70) plus the

voltage drop across the motor (95). If you had a voltmeter

and measured the voltage drop across the star LED (70) it

would be around 3.5V or greater. So Kirchoff’s voltage law

says that there’s less than 1V left to distribute across the

lamp (76) and motor (95) which is why they don’t function

properly.

WARNING: Moving parts. Do not

touch the motor during operation. Do

not lean over the motor.