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Optics
Fibroptonic
Ref : 202 012
3 Experiment no. 3
Reflection of an infrared beam. Acoustical detection.
Repeat the previous experiment but without aligning the transmitter and receiver. The 2
units are separated by a few centimetres. We then insert a glass slide or a small plane
mirror, which we adjust until an audible signal is heard (figure 8). We can thus illustrate
Snell's law for the reflection of an electromagnetic wave, which does not belong to the
visible region.
Figure 8: Reflection of an infrared beam
ENGLISH
2.3 Experiment:
After adjusting the potentiometer of the receiver unit to the maximum gain, try to align
the light transmitter and photoreceptor. When they are perfectly aligned, an audible
signal is heard even if the distance between the blue and black connectors is 10 to 15
cm. On the other hand, the red LED comes on only if the distance is less than 20 mm.
2.4 Conclusion:
The critical alignment of the transmitter and receiver indicates the significant directivity
of the infrared beam emitted. This experiment also illustrates the transformation of an
electrical signal into an infrared signal by the transmitter unit, the propagation of an
infrared signal in air and the opposite operation, which transforms an infrared signal into
an audible signal emitted by the loudspeaker on the receiver.
Signal generator
Transmitter
Receiver
Plane mirror
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