Data Sheet

-37-
43. Kirchhoff’s Current Law
Build the circuit shown on the left, turn on the switch (62) and
you will see that the Star LED (70) is on and the bi-directional
LED (71) is blue. Kirchhoff’s current law states: At any node
(junction) in an electrical circuit, the sum of currents owing
into that node is equal to the sum of currents owing out of
that node. Grid location C1 represents a node. If a positive
current is coming into a node and a negative current is leaving
a node, then:
I
battery
+ I
bi-directional LED
+ I
star LED
= 0
This shows that the current owing into node C1 from the
battery (91) must equal the current owing out of node C1 to
the bi-directional LED (71) plus the current owing out of node
C1 to the star LED (70).
44. Red and Blue Light Frequency
Replace the switch (62) with the press switch (61), press the
press switch (61) and you will see that the star LED (70) is
on and the bi-directional LED (71) is blue. Release the press
switch (61) and the star LED (70) and bi-directional LED (71)
will turn off. Project #34 discussed the wavelength of light.
Light can also be characterized in frequency, which is inversely
related of wavelength. Specically,
Frequency = (Speed of light)/Wavelength
Light travels at a constant speed of 300 million meters/
second (that’s fast!). So based on the wavelengths of red and
blue light discussed in project #34, we see that:
Frequency of Red Light = (3*10
8
)/(665*10
-9
) = ~451 THz
Frequency of Blue Light = (3*10
8
)/(470*10
-9
) = ~638 THz
THz stands for TeraHertz which is 10
12
Hertz. Hertz is the
measure of frequency representing one cycle per second.