What it shows
A light dependent resistor (LDR) has a high resistance in the dark and a low resistance in light. A transistor uses that change to switch the LED on when it gets dark.
This idea has a short entry only. For the science behind it, read the sentence above with your textbook and ask your teacher to explain the law or idea it shows, so you can describe it in your own words.
Materials
- An LDR
- A BC547 transistor
- Resistors, including a 10 kΩ variable resistor
- LEDs
- A 9 V battery and clip
- A breadboard and jumper wires
Safety
For this project: Battery power only.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesHow to go about it
Numbered steps have not been written for this idea yet. Plan it with your teacher: sketch the design with measurements, build one part at a time, test each part, and write every observation with the date. The free ebooks below have step-by-step projects of the same kind.
Free ebooks for this project
Find out more about electronics and robotics
Free, well-known places to explore the subject further. Ask a grown-up before you sign up for anything or type your name anywhere.