Transcript Dark Detecting Torch Presentation

School of Physics and Astronomy
How to make a dark
detecting torch
Chris Staddon – Senior Experimental Officer &
Outreach Officer
Michael Forrester – Student Helper
Acknowledgements:
Modified from: www.evilmadscientist.com/article.php/nightlight
School of Physics and Astronomy
Potential Divider Circuit
The Potential (Voltage) is shared between the resistances
LDR
Light - low resistance
Dark - high resistance
School of Physics and Astronomy
How it Works
The Mid-point needs 1.8 V
to switch on
0.6 V transistor +1.2 V LED
ratio of voltages
= ratio of resistances
so 1.8 / 3.0
= LDR / (2k4+LDR)
School of Physics and Astronomy
Components
• 1 x Prepared four-way
terminal block (Choc block)
• 1 x Prepared battery clip
• 1 x LED (Light Emitting
Diode – red)
• 1 x Transistor
• 1 x Resistor
Battery supplied separately
• 2 x Prepared wires (red and
black
School of Physics and Astronomy
Now build your torch !