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46
Temperature
sensor
YOU WILL NEED
+ 1 resistor, 470 Ω
+ 1 resistor, 3.3 kΩ
+ 1 red LED
+ 2 transistor modules
+ 3 short wire bridges
+ battery clip
+ electronics board
+ and additional
household items: 9-volt
square battery, hair dryer,
cube of ice
HERE'S HOW
1. Assemble the circuit, and then heat
transistor T1 with the hair dryer,
followed by transistor T2.
How does the LED react when you
heat the transistors?
2. Now for the cooling stage: First cool
down transistor T1 with the ice
cube, then transistor T2.
How does the LED react now?
R 1
3.3 k
T1
–
+
LED 1
R 2
470
+
9V
–
T2
EXPERIMENT 21
T2
R2
T1
470 Ω
C
R1
3.3 kΩ
LED1
A
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