Question

9. LED bulbs produce light of only one color. If you look at strings of lights, you’ll find that the number of bulbs in the series circuit varies with color: There are more bulbs in a string of red lights than in a string of blue lights. Explain why this is the case. How many bulbs would you expect in a string of red lights? Of blue lights? Explain your assumptions, using numbers and equations, in enough detail so that we can understand your reasoning.

Answer 1

The light produced by a LED depends on the voltage apllied between the terminals, i.e

We can see that the frequency of the light is directly proportional to the potential difference the electron is accelerated through. Blue light has higher frequency, and hence requres more voltage.

For a given supply voltage, the more bulbs there are in series, the less is the potential difference across each bulb.

Hence, there are more red bulbs in the series circuit than blue bulbs.