Current–voltage characteristic - Wikipedia
In this lesson, learn how to use a graph of current vs. potential difference to find the resistance of a resistor and to identify He connects five different batteries and gets the following values for current and voltage, shown in this table: Remember that Ohm's Law tells you the relationship between three. Calculate the gradient of the graph for the section where Ohm's law is obeyed. .. We are given the potential difference across the cell and the current in the circuit, The diagram shows an electric circuit consisting of a battery and four resistors . . Ohm's law describes the relationship between the total current I through an. An important relationship between the current, voltage and resistance in a current going through a resistor and the potential difference (voltage) across the same resistor. Apparatus. 4 cells, 4 resistors, an ammeter, a voltmeter, connecting wires .. The two circuits shown in the diagrams above are the same, except in the.
This decreased resistance resulting from increasing the number of branches will have the effect of increasing the rate at which charge flows also known as the current. In an effort to make this rather unexpected result more reasonable, a tollway analogy was introduced. A tollbooth is the main location of resistance to car flow on a tollway. Adding additional tollbooths within their own branch on a tollway will provide more pathways for cars to flow through the toll station.
These additional tollbooths will decrease the overall resistance to car flow and increase the rate at which they flow. Current The rate at which charge flows through a circuit is known as the current. Charge does NOT pile up and begin to accumulate at any given location such that the current at one location is more than at other locations. Charge does NOT become used up by resistors in such a manner that there is less current at one location compared to another.
In a parallel circuit, charge divides up into separate branches such that there can be more current in one branch than there is in another.
Nonetheless, when taken as a whole, the total amount of current in all the branches when added together is the same as the amount of current at locations outside the branches.
The rule that current is everywhere the same still works, only with a twist. The current outside the branches is the same as the sum of the current in the individual branches.
It is still the same amount of current, only split up into more than one pathway. Throughout this unit, there has been an extensive reliance upon the analogy between charge flow and water flow. Once more, we will return to the analogy to illustrate how the sum of the current values in the branches is equal to the amount outside of the branches.
The flow of charge in wires is analogous to the flow of water in pipes. Consider the diagrams below in which the flow of water in pipes becomes divided into separate branches.To study the dependence of potential difference (V) across a resister on the current (I)
At each node branching locationthe water takes two or more separate pathways. The rate at which water flows into the node measured in gallons per minute will be equal to the sum of the flow rates in the individual branches beyond the node. Similarly, when two or more branches feed into a node, the rate at which water flows out of the node will be equal to the sum of the flow rates in the individual branches that feed into the node.
The same principle of flow division applies to electric circuits. The rate at which charge flows into a node is equal to the sum of the flow rates in the individual branches beyond the node. This is illustrated in the examples shown below. In the examples a new circuit symbol is introduced - the letter A enclosed within a circle.
This is the symbol for an ammeter - a device used to measure the current at a specific point. An ammeter is capable of measuring the current while offering negligible resistance to the flow of charge.
Diagram A displays two resistors in parallel with nodes at point A and point B. Charge flows into point A at a rate of 6 amps and divides into two pathways - one through resistor 1 and the other through resistor 2.
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.
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.
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.
BBC - GCSE Bitesize: Resistance and Ohm's Law
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. In this type the resistance varies with the applied voltage or current. Negative resistance vs positive resistance: An I—V curve which is nonmonotonic having peaks and valleys represents a device which has negative resistance.
Regions of the curve which have a negative slope declining to the right represent operating regions where the device has negative differential resistancewhile regions of positive slope represent positive differential resistance. Negative resistance devices can be used to make amplifiers and oscillators.
Tunnel diodes and Gunn diodes are examples of components that have negative resistance.