Basic Circuit Analysis

Here we begin with one of the most important aspects of electronics; Ohms Law.
Ohm's Law is characterized as...

V = IR

...where V is the Voltage (Volts),
         I is the Current (Amps), and
         R is the Resistance (Ohms, omega symbol).

Notes: Equation was first proposed by Georg Simon Ohm (1787-1854).

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Here's a simple circuit with a 12 volt supply with a 500 ohm resistive load. By using Ohm's law, find the current (Amps).

V = IR

I = V/R

...where V is 12 volts
         R is 500 ohms

I = 12/500

  = 0.024 Amps or 24 milli-Amps (24mA)

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Here's another circuit with a 12 volt supply, but now with two 500 ohm resistors wired in series. Before finding the current, the total resistance must be found. Since the total resistors in the circuit are wired in series, the total resistance is found by adding all the resistor values.

Total R = R1 + R2
        = 500 + 500
        = 1000 ohms or 1k ohms

If there are more than 2 resistors, the total resistance would be the sum of all the resistors in series.

Total R = R1 + R2 + R3...+ Rn

By using Ohm's law, find the current (Amps).

V = IR

I = V/Total R

...where V is 12 volts
         Total R is 1k ohms

I = 12/1k
  = 0.012 Amps or 12 milli-Amps (12mA)

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Here's another circuit with a 12 volt supply, but now with two 500 ohm resistors wired in parallel. Again, the total resistance must be found. Since the total resistors in the circuit are wired in parallel, the total resistance is found by using the following formula:

Total R = 1/(1/R1 + 1/R2)
        = 1/(1/500 + 1/500)
        = 250 ohms

If there are more than 2 resistors, the total resistance would be found using the formula below.

Total R = 1/(1/R1 + 1/R2 + 1/R3...+ 1/Rn)

By using Ohm's law, find the current (Amps).

V = IR

I = V/Total R

...where V is 12 volts
         Total R is 250 ohms

I = 12/250
  = 0.048 Amps or 48 milli-Amps (48mA)

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Here's another circuit with a 12 volt supply, but now there's a combination of resistors that are wired in parallel and in series. In order to find the total resistance, the total resistance in parallel must first be found using the formula below.

Total R parallel = 1/(1/R2 + 1/R3)
                 = 1/(1/500 + 1/500)
                 = 250 ohms

The circuit would look like this after calculating the parallel resistance. Now, calculate the total resistance in series.

Total R = R1 + Total R (parallel)
        = 500 + 250
        = 750 ohms

Now, find the total current by using Ohm's Law.

V = IR

I = V/Total R

...where V is 12 volts
         Total R is 750 ohms

I = 12/750
  = 0.016 Amps or 16 milli-Amps (16mA)

More to come...