electrical resistance - relationship between voltage and current - Physics Stack Exchange
proportional relationship between resistance and current would have to use and Inverse Proportional relationships, they may become confused and have. All materials are made up from atoms, and all atoms consist of protons, neutrons and electrons. Protons, have a positive electrical charge. Neutrons have no. if we say resistance is constant, then power must change with current, There is no contradiction here, you simply need to be mindful of what.
A piece of conducting material of a particular resistance meant for use in a circuit is called a resistor. Conductors are made of high- conductivity materials such as metals, in particular copper and aluminium.
Resistors, on the other hand, are made of a wide variety of materials depending on factors such as the desired resistance, amount of energy that it needs to dissipate, precision, and costs.
Ohm's law The current-voltage characteristics of four devices: Two resistorsa diodeand a battery. The horizontal axis is voltage dropthe vertical axis is current. Ohm's law is satisfied when the graph is a straight line through the origin.Electric Current & Circuits Explained, Ohm's Law, Charge, Power, Physics Problems, Basic Electricity
Therefore, the two resistors are ohmic, but the diode and battery are not. For many materials, the current I through the material is proportional to the voltage V applied across it: Therefore, the resistance and conductance of objects or electronic components made of these materials is constant.
This relationship is called Ohm's lawand materials which obey it are called ohmic materials. Examples of ohmic components are wires and resistors. The current-voltage IV graph of an ohmic device consists of a straight line through the origin with positive slope.
Current, Voltage and Resistance
Other components and materials used in electronics do not obey Ohm's law; the current is not proportional to the voltage, so the resistance varies with the voltage and current through them.
These are called nonlinear or nonohmic. Examples include diodes and fluorescent lamps. The IV curve of a nonohmic device is a curved line. Relation to resistivity and conductivity[ edit ] Main article: Electrical resistivity and conductivity A piece of resistive material with electrical contacts on both ends. The resistance of a given object depends primarily on two factors: What material it is made of, and its shape.
Current, Voltage and Resistance - Humane Slaughter Association
For a given material, the resistance is inversely proportional to the cross-sectional area; for example, a thick copper wire has lower resistance than an otherwise-identical thin copper wire.
Also, for a given material, the resistance is proportional to the length; for example, a long copper wire has higher resistance than an otherwise-identical short copper wire. The resistance R and conductance G of a conductor of uniform cross section, therefore, can be computed as R. The resistance R of a material depends on its length, cross-sectional area, and the resistivity the Greek letter rhoa number that depends on the material: The resistivity and conductivity are inversely related.
Good conductors have low resistivity, while poor conductors insulators have resistivities that can be 20 orders of magnitude larger. Resistance also depends on temperature, usually increasing as the temperature increases. For reasonably small changes in temperature, the change in resistivity, and therefore the change in resistance, is proportional to the temperature change.
This is reflected in the equations: At low temperatures some materials, known as superconductors, have no resistance at all. Resistance in wires produces a loss of energy usually in the form of heatso materials with no resistance produce no energy loss when currents pass through them. Ohm's Law In many materials, the voltage and resistance are connected by Ohm's Law: These materials are called non-ohmic.
We'll focus mainly on ohmic materials for now, those obeying Ohm's Law. Example A copper wire has a length of m and a diameter of 1. If the wire is connected to a 1. The V is the battery voltage, so if R can be determined then the current can be calculated. The first step, then, is to find the resistance of the wire: L is the length, 1.
The resistivity can be found from the table on page in the textbook. The area is the cross-sectional area of the wire. This can be calculated using: The resistance of the wire is then: The current can now be found from Ohm's Law: It has units of Watts.
Batteries and power supplies supply power to a circuit, and this power is used up by motors as well as by anything that has resistance. The power dissipated in a resistor goes into heating the resistor; this is know as Joule heating.
In many cases, Joule heating is wasted energy. In some cases, however, Joule heating is exploited as a source of heat, such as in a toaster or an electric heater. The electric company bills not for power but for energy, using units of kilowatt-hours. It does add up, though. The following equation gives the total cost of operating something electrical: Try this at home - figure out the monthly cost of using a particular appliance you use every day. Possibilities include hair dryers, microwaves, TV's, etc.
The power rating of an appliance like a TV is usually written on the back, and if it doesn't give the power it should give the current. Anything you plug into a wall socket runs at V, so if you know that and the current you can figure out how much power it uses. The cost for power that comes from a wall socket is relatively cheap. On the other hand, the cost of battery power is much higher. Although power is cheap, it is not limitless.
Electricity use continues to increase, so it is important to use energy more efficiently to offset consumption. Appliances that use energy most efficiently sometimes cost more but in the long run, when the energy savings are accounted for, they can end up being the cheaper alternative.
Electrical resistance and conductance
Direct current DC vs. If the circuit has capacitors, which store charge, the current may not be constant, but it will still flow in one direction.
The current that comes from a wall socket, on the other hand, is alternating current. With alternating current, the current continually changes direction. This is because the voltage emf is following a sine wave oscillation.
For a wall socket in North America, the voltage changes from positive to negative and back again 60 times each second.