# Resistors: Explanations and Calculations

(1) I have five circuits and want to run each one, one at a time, and then all five at the same time. My source is 12Vdc and 1500mA. The first circuit is 1.992 Mega ohms, the second is 3248 ohms, the third is 13.2k ohms, and the fourth is 0.247 Mega ohms and the fifth is .777k ohms. Now, the first four circuits use 5V and the fifth uses 9V.

First, how do calculate or get a resistor with this information to both limit the current for each circuit and make sure I get the right voltage for each circuit and then run each one at a time and then all at once.

(2) Next, if I have 12Vdc and 1500mA going into a resistor then to and led then to ground, how do I figure the resistor that will protect the lead?

(3) Finally, how do I measure I in a circuit?

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#### Solution Preview

Question 1:

You need to connect a resistance, say R Ohms, in series with the source and then feed the load (circuit, as you called it) which is characterised by a Voltage Vl and resistance Rl.

Now, you CANNOT have a single value of R which will give you the right voltage to each circuit. R depends on both Vl and Rl. For each combination of (Vl,Rl), you need a separate R and then a separate R to run all the first four(You cannot run all the five all at once since the fifth circuit needs 9 Volts while the first ...

#### Solution Summary

The solution involves an explanation of resistors and calculations of the voltage of each circuit (in a series of five circuits) when run individually, and as a group. In addition, an explanation of how a resistor protects a lead is given, as well as the method for measuring current in a circuit.