For circuit (a) below, determine if the LED lights up. For circuit (b) below, which LED is
brightest and which is dimmest? Show work.

Here's the picture:
http://postimage.org/image/rjctt2w6z/

Question

For circuit (a) below, determine if the LED lights up. For circuit (b) below, which LED is
brightest and which is dimmest? Show work.

Here's the picture:
http://postimage.org/image/rjctt2w6z/

anonymous · Answer

For a), the big question is when a LED is on. DO you have an idea of when a diode (in general) will conduct?

As for b), what makes a LED glow brighter? Is it voltage, or current or something else?

whpalmer4 · Answer

The voltage across the LED in a) is 5v * (200 ohms/(200 ohms+300 ohms+100ohms)) = 5/3 V.  As I recall, that's too low for most LEDs, usually need 2 V or more.