Ohm’s Law - How Voltage, Current, and Resistance Relate | Ohm's Law | Electronics Textbook
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Electronic engineers use these charts to determine basic parameters of a device and to model its behavior in an electrical circuit. These characteristics are also known as I—V curves, referring to the standard symbols for current and voltage. In electronic components with more than two terminals, such as vacuum tubes and transistorsthe current-voltage relationship at one pair of terminals may depend on the current or voltage on a third terminal.
This is usually displayed on a more complex current—voltage graph with multiple curves, each one representing the current-voltage relationship at a different value of current or voltage on the third terminal. The simplest I—V curve is that of a resistorwhich according to Ohm's law exhibits a linear relationship between the applied voltage and the resulting electric current ; the current is proportional to the voltage, so the I—V curve is a straight line through the origin with positive slope.
The reciprocal of the slope is equal to the resistance. The I—V curve of an electrical component can be measured with an instrument called a curve tracer. The transconductance and Early voltage of a transistor are examples of parameters traditionally measured from the device's I—V curve.
Types of I—V curves[ edit ] The shape of an electrical component's characteristic curve reveals much about its operating properties. I—V curves of different devices can be grouped into categories: The quadrants of the I—V plane. Power sources have curves passing through the red regions.
Devices which have I—V curves which are limited to the first and third quadrants of the I—V plane, passing through the originare passive components loadsthat consume electric power from the circuit.
Current–voltage characteristic - Wikipedia
Examples are resistors and electric motors. Conventional current always flows through these devices in the direction of the electric fieldfrom the positive voltage terminal to the negative, so the charges lose potential energy in the device, which is converted to heat or some other form of energy.
In contrast, devices with I—V curves which pass through the second or fourth quadrants are active componentspower sourceswhich can produce electric power.
- Relationship and Difference Between Voltage, Current and Resistance
- Ohm’s Law - How Voltage, Current, and Resistance Relate
Examples are batteries and generators. When it is operating in the second or fourth quadrant, current is forced to flow through the device from the negative to the positive voltage terminal, against the opposing force of the electric field, so the electric charges are gaining potential energy.
Thus the device is converting some other form of energy into electric energy. A straight line through the origin represents a linear circuit element, while a curved line represents a nonlinear element. For example, resistors, capacitors, and inductors are linear, while diodes and transistors are nonlinear.
An I—V curve which is a straight line through the origin with positive slope represents a linear or ohmic resistor, the most common type of resistance encountered in circuits.
It obeys Ohm's law ; the current is proportional to the applied voltage over a wide range. Its resistanceequal to the reciprocal of the slope of the line, is constant. A curved I—V line represents a nonlinear resistance, such as a diode. Standardized letters like these are common in the disciplines of physics and engineering, and are internationally recognized. Each unit of measurement is named after a famous experimenter in electricity: The amp after the Frenchman Andre M.
The mathematical symbol for each quantity is meaningful as well. Most direct-current DC measurements, however, being stable over time, will be symbolized with capital letters.
Coulomb and Electric Charge One foundational unit of electrical measurement, often taught in the beginnings of electronics courses but used infrequently afterwards, is the unit of the coulomb, which is a measure of electric charge proportional to the number of electrons in an imbalanced state. One coulomb of charge is equal to 6,,, electrons. Cast in these terms, current is the rate of electric charge motion through a conductor. As stated before, voltage is the measure of potential energy per unit charge available to motivate electrons from one point to another.
Defined in these scientific terms, 1 volt is equal to 1 joule of electric potential energy per divided by 1 coulomb of charge. Thus, a 9 volt battery releases 9 joules of energy for every coulomb of electrons moved through a circuit. These units and symbols for electrical quantities will become very important to know as we begin to explore the relationships between them in circuits.
Ohm expressed his discovery in the form of a simple equation, describing how voltage, current, and resistance interrelate: In this algebraic expression, voltage E is equal to current I multiplied by resistance R.AC Voltage Circuts (Cycles, Periods, & Frequency)
Using algebra techniques, we can manipulate this equation into two variations, solving for I and for R, respectively: In the above circuit, there is only one source of voltage the battery, on the left and only one source of resistance to current the lamp, on the right.