Limited Energy Calculations

A Review of Ohm’s Law

Kirchoff’s Law & Voltage Drop

Calculations

WARNING!!! BEFORE STARTING THIS COURSE

YOU WILL NEED TO HAVE THE FOLLOWING AT HAND:1. The NEC2. A copy of the LERC PDF on Calculations (downloaded at this site).3. A battery operated calculator that has a M+, M- and MRC keys.

Ohm’s Law Formula Wheel

Ohm’s Law Rules

• 1. Always solve parallel portions of the circuit first then use those answers to solve the series portion of the problem

• 2. In a series circuit voltages are added, in a parallel circuit voltage is constant.

• 3. In a series circuit current is constant, in a parallel circuit currents are added.

Ohm’s Law and Resistance's• In a series circuit resistance is added.

R1 + R2 + R3 = RT

• A circuit with 2 resistors in parallel we use R1 x R2 / R1 + R2 = RT

• in parallel circuits having more than 2 parallel resistance's it really gets confusing but we have a new way of solving any amount of resistors in parallel with a simple calculator

Calculator Solution to Parallel Resistors

• Lets take a circuit with three parallel resistors

• R1 = 3 • R2 = 6 • R3 = 9

Kirchoff’s Voltage Law

• The sum of the voltage drop is always equal to the source voltage.

• Remember: whenever you are using Ohm’s law you can also invoke Kirchoff’s law and vice-versa.

Calculation of Parallel Resistors

• First turn on and clear your calculators memory (MRC, C, C) the memory should be clear now.

• Now enter the resistors as follows: 1 / 3 M+ 1 / 6 M+ 1 /9 M+

• Now to get the answer do the following: 1 / MRC = this should display 1.6363639

Lets try a few problems

Next we have a few problems for you to work on. Use both sets of laws to work them.

First you will see the problem only. Try to find the total resistance of the circuit.

After you have work the problem yourself THEN right click to solve the problem step by step using both sets of laws.

Ohm’s Law - #1

R1 = 3 R2 = 5

R3 = 2

R4 = 4

R5 = 5

Ohm’s Law - #1

• Solve for RT (Total Resistance)

RA = 1.05 • First solve for the parallel circuit

this gives us a subtotal for RA of

• Now add the two remaining resistors to get RT

R1 = 3 R2 = 5

R3 = 2

R4 = 4

R5 = 5

RT = 9.05

Ohm’s Law - #2

• 1st Solve for the parallel of R3 and R4

• 2nd Solve the series circuit of R2, RA and R5

• 3rd Solve the parallel of R1 and RB

• Solve for RT (Total Resistance)

R1=4 R2 = 2 R3 = 3 R4 = 5

R5 = 6

RA = 1.875

RB = 9.875

RT = 2.84

Ohm’s Law - #3

• 2nd Solve for the parallel of RA and R4

• 1st Solve for the series of R2 and R3

• 3rd Solve for the series of R1 and RB

• Solve for RT (Total Resistance)

R1 = 2 R3 = 6

R4 = 8

R2 = 4

RA = 10

RB = 4.44

RT = 6.44

Ohm’s Law - #4

• 3rd Solve the parallel of R2, R3 & RB

• 2nd Solve the series of R4, RA, & R7

• 4th Solve the series of R1, RC, & R8

• 1st Solve for the parallel of R5 and R6

R1=2 R2= 4 R3=6 R4= 8 R6=12

R8 =16 R7=14 R5 = 10

RA = 5.45

RB = 27.45

RC = 2.2

RT = 20.2

Completing the Circuit Calculations

• Up to this point our problems have dealt primarily with resistance issues.

• Remember, in order for a circuit to have resistance it must have volts and amps also.

NOW > Go over all your formula and get use to how they interact to find ALL the measurements of a circuit, through each of the items in the circuit.

Quiz 1