"David D" wrote in message
oups.com...
I have this question and I am wondering if someone can tell
me the
formula and how they derived the answer (steps) - it is
probably
simple, but I am learning this as I go :

Electronic
1) A simple circuit consists of a current limiting resistor
in series
with an LED across a supply voltage of 5VDC. The forward
voltage drop
is 1.5VDC and the forward current is 10mA. The series
resistor would
have a value of:
a. 1kΩ
b. 500Ω
c. 350Ω
d. 100Ω

OK you need to conduct 10ma through a resistor with 5 - 1.5
= 3.5 volts across it. Since R = 3.5/.01, you can take it
from there.
Is this a homework assignment? If so and you can not figure
this out, switch majors.

David