PS-6.7 Use the formula V = IR to solve problems related to electric circuits.
Key Concepts:
Voltage: volt
Current: amp
Resistance: ohm
Ohms law: V = IR  
The relationship between electrical resistance, current, and voltage is defined by the mathematical relationship V= IR and is referred to as Ohm's law. In this equation "V" stands for voltage, measured in volts, "I" stands for current, measured in amperes, and "R" stands for resistance, measured in Ohms (Ω ).
Common sources of voltage in circuits may be chemical cells (a battery is a combinations of cells) and generators. Sources of electrical resistance in circuits may include resistors, light bulb filaments, wire conductors and other electric devices.
When solving Ohm's law problems you are expected to solve for any unknown variable. Here are several example problems.
Example #1. Determine the voltage of the circuit shown below in diagram "A".
Diagram A  
In this circuit we are given the current from the ammeter .2A. We also can determine the resistance. Since this is a series circuit the total resistance is the sum of the resistances of L1 and L2, 70Ω . We set the problem up and solve it like this.
V=IR
V=.2A 70Ω
V= 14V
The answer is 14V
Example #2. Look at the diagram below and determine the resistance of the circuit.
 
In this circuit we are given the current from the ammeter .4A. We are also given the voltage, 6V. To solve for the resistance we set the problem up and solve it like this.
R=V/I
    R=6V/.4A
  R= 15Ω
The answer is 15Ω
Example #3. Look at the circuit diagram below and determine the current.
 
In this third example we are given the voltage and the resistance. We must solve for the current. We set the problem up and solve it like this:
I=V/R
        I=2V / 3.3Ω
I= .6A
The answer is .6A