Asked by: Abi
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Q:
I am thinking of buying some 5mm led bulbs to use in a science project with children in my class. They will need to make a circuit to light up the bulb. Another teacher said she did thus using a cell battery - a cr2032 I think. Will this be the right battery to use with these bulbs and would they work also with the colour changing bulbs? Thank you, Abi
A:
The ultra-bright red LED has a forward voltage drop of about 1.9V so in theory with a 3V CR2032 cell you would want to use a current limit resistor something like a 68 ohm or a 100 ohm. However the coin cell can only deliver a limited amount of current so in reality you are often able to get away without using a current limit resistor. The colour changing LED is rated between 2.7V and 5V so would work fine off a coin cell battery, though it won't be at full brightness again because the coin cell won't deliver enough current to run at full brightness, but it will still work fine.
Answered by: Geoff Hampso
07-Nov-11
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