The direction of electric fields is always defined as the direction a positive test charge would move if it was dropped in the field. The test charge has to be infinitely small, to keep its charge from influencing the field. We can begin by constructing electric fields for solitary positive and negative charges.
If you dropped a positive test charge near a negative charge, the test charge would be attracted towards the negative charge. So, for a single, negative charge we draw our electric field arrows pointing inward at all directions. That same test charge dropped near another positive charge would result in an outward repulsion, which means we draw arrows going out of the positive charge. The electric fields of single charges. A negative charge has an inward electric field because it attracts positive charges.
The positive charge has an outward electric field, pushing away like charges. The uniform e-field above points away from the positive charges, towards the negatives. Imagine a tiny positive test charge dropped in the e-field; it should follow the direction of the arrows.
As we've seen, electricity usually involves the flow of electrons--negative charges--which flow against electric fields. Electric fields provide us with the pushing force we need to induce current flow. An electric field in a circuit is like an electron pump: a large source of negative charges that can propel electrons, which will flow through the circuit towards the positive lump of charges.
When we harness electricity to power our circuits, gizmos, and gadgets, we're really transforming energy. Electronic circuits must be able to store energy and transfer it to other forms like heat, light, or motion. The stored energy of a circuit is called electric potential energy.
To understand potential energy we need to understand energy in general. Energy is defined as the ability of an object to do work on another object, which means moving that object some distance. Energy comes in many forms , some we can see like mechanical and others we can't like chemical or electrical. Regardless of what form it's in, energy exists in one of two states : kinetic or potential.
An object has kinetic energy when it's in motion. The amount of kinetic energy an object has depends on its mass and speed. Potential energy , on the other hand, is a stored energy when an object is at rest. It describes how much work the object could do if set into motion.
It's an energy we can generally control. When an object is set into motion, its potential energy transforms into kinetic energy. Let's go back to using gravity as an example. A bowling ball sitting motionless at the top of Khalifa tower has a lot of potential stored energy. Once dropped, the ball--pulled by the gravitational field--accelerates towards the ground.
As the ball accelerates, potential energy is converted into kinetic energy the energy from motion. Eventually all of the ball's energy is converted from potential to kinetic, and then passed on to whatever it hits.
When the ball is on the ground, it has a very low potential energy. Just like mass in a gravitational field has gravitational potential energy, charges in an electric field have an electric potential energy.
A charge's electric potential energy describes how much stored energy it has, when set into motion by an electrostatic force, that energy can become kinetic, and the charge can do work. Like a bowling ball sitting at the top of a tower, a positive charge in close proximity to another positive charge has a high potential energy; left free to move, the charge would be repelled away from the like charge.
A positive test charge placed near a negative charge would have low potential energy, analogous to the bowling ball on the ground. To instill anything with potential energy, we have to do work by moving it over a distance.
In the case of the bowling ball, the work comes from carrying it up floors, against the field of gravity. Similarly, work must be done to push a positive charge against the arrows of an electric field either towards another positive charge, or away from a negative charge.
The further up the field the charge goes, the more work you have to do. Likewise, if you try to pull a negative charge away from a positive charge--against an electric field--you have to do work.
For any charge located in an electric field its electric potential energy depends on the type positive or negative , amount of charge, and its position in the field. Electric potential energy is measured in units of joules J.
Electric potential builds upon electric potential energy to help define how much energy is stored in electric fields.
It's another concept which helps us model the behavior of electric fields. Electric potential is not the same thing as electric potential energy! At any point in an electric field the electric potential is the amount of electric potential energy divided by the amount of charge at that point.
It takes the charge quantity out of the equation and leaves us with an idea of how much potential energy specific areas of the electric field may provide. In any electric field there are two points of electric potential that are of significant interest to us. There's a point of high potential, where a positive charge would have the highest possible potential energy, and there's a point of low potential, where a charge would have the lowest possible potential energy.
One of the most common terms we discuss in evaluating electricity is voltage. A voltage is the difference in potential between two points in an electric field. Voltage gives us an idea of just how much pushing force an electric field has. With potential and potential energy under our belt we have all of the ingredients necessary to make current electricity.
Let's do it! After studying particle physics, field theory, and potential energy, we now know enough to make electricity flow. Let's make a circuit! Batteries are common energy sources which convert chemical energy to electrical energy.
They have two terminals, which connect to the rest of the circuit. On one terminal there are an excess of negative charges, while all of the positive charges coalesce on the other. This is an electric potential difference just waiting to act! If we connected our wire full of conductive copper atoms to the battery, that electric field will influence the negatively-charged free electrons in the copper atoms. Simultaneously pushed by the negative terminal and pulled by the positive terminal, the electrons in the copper will move from atom to atom creating the flow of charge we know as electricity.
After a second of the current flow, the electrons have actually moved very little--fractions of a centimeter. However, the energy produced by the current flow is huge , especially since there's nothing in this circuit to slow down the flow or consume the energy. Connecting a pure conductor directly across an energy source is a bad idea. Energy moves very quickly through the system and is transformed into heat in the wire, which may quickly turn into melting wire or fire.
Instead of wasting all that energy, not to mention destroying the battery and wire, let's build a circuit that does something useful! Generally an electric circuit will transfer electric energy into some other form--light, heat, motion, etc. If we connect a light bulb to the battery with wires in between, we have a simple, functional circuit. Schematic: A battery left connecting to a lightbulb right , the circuit is completed when the switch top closes.
With the circuit closed, electrons can flow, pushed from the negative terminal of the battery through the lightbulb, to the positive terminal. While the electrons move at a snails pace, the electric field affects the entire circuit almost instantly we're talking speed of light fast. Electrons throughout the circuit, whether at the lowest potential, highest potential, or right next to the light bulb, are influenced by the electric field.
When the switch closes and the electrons are subjected to the electric field, all electrons in the circuit start flowing at seemingly the same time. Those charges nearest the light bulb will take one step through the circuit and start transforming energy from electrical to light or heat.
In this tutorial we've uncovered just a tiny portion of the tip of the proverbial iceberg. There's still a ton of concepts left uncovered. From here we'd recommend you step right on over to our Voltage, Current, Resistance, and Ohm's Law tutorial. Now that you know all about electric fields voltage and flowing electrons current , you're well on your way to understanding the law that governs their interaction. See our Engineering Essentials page for a full list of cornerstone topics surrounding electrical engineering.
Take me there! For more information and visualizations explaining electricity, visit this site. Or, maybe you'd like to learn something practical? In that case, check out some of these basic level skill tutorials:. Need Help? Mountain Time: Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. Physical Science. Electricity lights up our world, but where does it come from? See more nuclear power pictures. Science Green Science How can electricity increase my car's fuel efficiency?
Cite This! Print Citation. Try Our Crossword Puzzle! The generator, in turn, converts the mechanical kinetic energy of the rotor to electrical energy. Different types of turbines include steam turbines, combustion gas turbines, hydroelectric turbines, and wind turbines. Most steam turbines have a boiler in which a fuel is burned to produce hot water and steam in a heat exchanger, and the steam powers a turbine that drives a generator. Nuclear power reactors use nuclear fuel rods to produce steam.
Solar thermal power plants and most geothermal power plants use steam turbines. Most of the largest U. Combustion gas turbines , which are similar to jet engines, burn gaseous or liquid fuels to produce hot gases to turn the blades in the turbine. Steam and combustion turbines can be operated as stand-alone generators in a single-cycle or combined in a sequential combined-cycle. Combined-cycle systems use combustion gases from one turbine to generate more electricity in another turbine.
Most combined-cycle systems have separate generators for each turbine. In single-shaft combined cycle systems, both turbines may drive a single generator. Learn more about different types of combined-cycle power plants. Combined-heat-and-power CHP plants , which may be referred to as cogenerators , use the heat that is not directly converted to electricity in a steam turbine, combustion turbine, or an internal combustion engine generator for industrial process heat or for space and water heating.
Most of the largest CHP plants in the United States are at industrial facilities such as pulp and paper mills, but they are also used at many colleges, universities, and government facilities.
CHP and combined-cycle power plants are among the most efficient ways to convert a combustible fuel into useful energy. Hydroelectric turbines use the force of moving water to spin turbine blades to power a generator. Most hydroelectric power plants use water stored in a reservoir or diverted from a river or stream. Pumped-storage hydropower plants use the same types of hydro turbines that conventional hydropower plants use, but they are considered electricity storage systems see below.
Other types of hydroelectric turbines called hydrokinetic turbines are used in tidal power and wave power systems. Learn more about different types of hydroelectric turbines. Wind turbines use the power in wind to move the blades of a rotor to power a generator. There are two general types of wind turbines : horizontal axis the most common and vertical-axis turbines.
Ocean thermal energy conversion OTEC systems use a temperature difference between ocean water at different depths to power a turbine to produce electricity. There are many different types of electricity generators that do not use turbines to generate electricity.
The most common in use today are solar photovoltaic PV systems and internal combustion engines. Solar photovoltaic cells convert sunlight directly into electricity.
They are used to power devices as small as wrist watches and can be connected together in panels that are connected together in arrays to power individual homes or form large power plants.
Photovoltaic PV power plants are now one of the fastest growing sources of electricity generation around the world. Internal combustion engines , such as diesel engines, are used all around the world for electricity generation including in many remote villages in Alaska. They are also widely used for mobile power supply at construction sites and for emergency or backup power supply for buildings and power plants.
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