Introduction Basic Principles History of ET Present State of ET
The Physics Properties of Electricity Current Flow & Ohm's Law Induction & Inductance Self Inductance Mutual Inductance Circuits & Phase Impedance Depth & Current Density Phase Lag
Instrumentation Eddy Current Instruments Resonant Circuits Bridges Impedance Plane Display - Analog Meter
Procedures Issues Reference Standards Signal Filtering
Applications Surface Breaking Cracks SBC using Sliding Probes Tube Inspection Conductivity Heat Treat Verification Thickness of Thin Mat'ls Thickness of Coatings
Advanced Techniques Scanning Multi-Frequency Tech. Swept Frequency Tech. Pulsed ET Tech. Background Pulsed ET Remote Field Tech.
Quizzes
Formulae& Tables EC Standards & Methods EC Material Properties -
Current Flow and Ohm's Law
Ohm's law is the most important, basic law of electricity. It defines the relationship between the three fundamental electrical quantities: current, voltage, and resistance. When a voltage is applied to a circuit containing only resistive elements (i.e. no coils), current flows according to Ohm's Law, which is shown below.
I = V / R 
Where:
I =
Electrical Current (Amperes)
V =
Voltage (Voltage)
R =
Resistance (Ohms)
Ohm's law states that the electrical current (I) flowing in an circuit is proportional to the voltage (V) and inversely proportional to the resistance (R). Therefore, if the voltage is increased, the current will increase provided the resistance of the circuit does not change. Similarly, increasing the resistance of the circuit will lower the current flow if the voltage is not changed. The formula can be reorganized so that the relationship can easily be seen for all of the three variables.
The Java applet below allows the user to vary each of these three parameters in Ohm's Law and see the effect on the other two parameters. Values may be input into the dialog boxes, or the resistance and voltage may also be varied by moving the arrows in the applet. Current and voltage are shown as they would be displayed on an oscilloscope with the X-axis being time and the Y-axis being the amplitude of the current or voltage. Ohm's Law is valid for both direct current (DC) and alternating current (AC). Note that in AC circuits consisting of purely resistive elements, the current and voltage are always in phase with each other.
Exercise: Use the interactive applet below to investigate the relationship of the variables in Ohm's law. Vary the voltage in the circuit by clicking and dragging the head of the arrow, which is marked with the V. The resistance in the circuit can be increased by dragging the arrow head under the variable resister, which is marked R. Please note that the vertical scale of the oscilloscope screen automatically adjusts to reflect the value of the current.
See what happens to the voltage and current as the resistance in the circuit is increased. What happens if there is not enough resistance in a circuit? If the resistance is increased, what must happen in order to maintain the same level of current flow?
A wave is a transmission of a disturbance from one point to another. It involves the transmission of energy from a source to other points.
<em><u>Waves may classified as longitudinal waves or transverse waves depending on the vibration of particles relative to the wave motion.</u></em>
<em><u>Longitudinal waves are waves in which the vibration of particles is parallel to the direction of the wave motion, while transverse wave are types of waves in which the vibration of particles is perpendicular to the wave motion.</u></em>
Longitudinal waves creates regions of compressions and rarefactions, while transverse waves creates regions of maximum displacement called crests and troughs
