Producing Electric Current (Phys. Sci. 7.3)
Presentation
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Physics, Science
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11th - 12th Grade
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Practice Problem
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Easy
Rachel Rapp
Used 5+ times
FREE Resource
19 Slides • 6 Questions
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Producing Electric Current (Phys. Sci. 7.3)
Main Idea: A changing magnetic field produces an electric current in a wire loop.
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Electromagnetic Induction
Working independently in 1831, Michael Faraday in Britain and Joseph Henry in the U.S. both found that moving a loop of wire through a magnet field caused an electric current in the wire. They also found that moving a magnet through a loop of wire produces a current. In both cases, mechanical energy of movement in the wire is converted to electricalenergy in the wire
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Electromagnetic Induction
When the magnet and wire loop are moving relative to each other, the magnetic field inside the loop changes with time and induces (which means generates) an electric current in the wire coil. The generation of an electric current by a changing magnetic field is ELECTROMAGNETIC INDUCTION.
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Electromagnetic Induction
Electromagnetic induction can occur in other ways, too. for example, if the current in a wire changes with time, then the magnetic field around the wire is also changing. This changing magnetic field can induce a current in a nearby coil. Both types of electromagnetic induction are important to generating and transmitting the electrical energy that we use.
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Generators
Most of the electrical energy that you use every day is provided by generators. A GENERATOR uses electromagnetic induction to transform mechanical energy into electrical energy. The photo shows a hand-operated generator being used to power a flashlight. The mechanical energy is provided by turning the handle. The generator transforms the mechanical energy into electrical energy, which lights the bulb.
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Simple Generators
A diagram of a simple generator is shown here. A current is produced in the coil as the coil rotates between the poles of a permanent magnet. As the generator's wire coil rotates through the magnetic field of the perm. magnet, a current is induced in the coil. After the coil makes 1/2 of a turn, the ends are moving past the opposite poles of the perm. magnet. This changes the direction of the current.
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Simple Generators
As the coil keeps rotating, the current that is produced continues to change direction. The direction of the current in the coil changes twice with each turn. The frequency with which the current changes can be controlled by changing the rotation rate of the generator. In the U.S., electrical energy for home use is produced by generators that rotate 60 times per second (60 Hz). Therefore, the current changes direction 120 times every second.
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Using Electric Generators
Generators similar to simple generators are used in cars, where they are called alternators. The alternator provides electrical energy to operate lights and other accessories. Spark plugs in the engine also use this electrical energy to ignite the fuel in the cylinders of the engine. Once the engine is running, it provides the mechanical energy that is used to turn the coil in the alternator.
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Rotating the Permanent Magnet
Suppose that the coil in a generator were fixed and the perm. magnet rotated instead. The current generated would be the same as when the coil rotates and the magnet does not move. The huge generators used in electrical power plants are made this way. Mechanical energy is used to rotate the magnet, and the current is induced in the stationary coil.
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Generating Electricity for Your Home
Unless you have a generator in your home, the electrical energy you use comes from a power plant. Each plant must have an energy source. Some burn fossil fuels or use nuclear reactions to produce thermal energy, which heats water into steam, which in turn pushes the turbine blades.
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Turbines
A TURBINE is a large wheel that rotates when pushed by water, wind, or steam. In some areas, fields of windmills, like those shown here, can be used to capture the mechanical energy of wind. Other power plants use mechanical energy in falling water to drive the turbine. The turbine is connected to the rotating magnet in the generator. The EMs in these generators have many coils wrapped around the iron cores. The generator changes the mechanical energy of the turbine into electrical energy that you use.
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Generators and Motors
Both generators and electric motors use electromagnets to convert electrical and mechanical energy.
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Direct & Alternating Currents
Because power outages can occur, some devices use batteries as a backup energy source. However, the current produced by a battery is different than a current produced by a generator. A battery produces a direct current, and a generator that supplies an outlet produces an alternating current.
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Direct Current (DC)
DIRECT CURRENT (DC) is electric current that is always moving in one direction through a wire.
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AC
ALTERNATING CURRENT (AC) is electric current that reverses the direction in a regular pattern. In North America, the alternating current in a wall socket has a frequency of 60 Hz and an average voltage of 120 V. Electronic devices that use backup batteries usually require direct current to operate. The device's electronic components reduce the voltage of the alternating current and convert it to direct current.
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Transformers
To reduce the voltage without changing the amount of electrical energy, many devices use transformers. A TRANSFORMER is a device that increases or decreases the voltage of an alternating current. A transformer is made of a primary coil and a secondary coil wrapped around the same iron core. A transformer that increases the voltage is called a step-up transformer, and a transformer that decreases voltage is called a step-down transformer.
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How They Work
As an alternating current passes through the primary coil, the coils magnetic field magnetizes the iron core. The primary coil's magnetic field changes direction at the same frequency as the current in the primary coil. The magnetic field in the iron core also changes direction at that frequency. The changing magnetic field in the iron core induces an alternating current in the secondary coil. The input and output current alternate at the same frequency.
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Calculate Output Voltage
The output voltage of a transformer depends on the input voltage and the number of turns in the primary and secondary coils. This relationship can be expressed in an equation:
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Transmitting Electricity
Electrical energy is often transmitted along wires known as power lines. During transmission, some of the electrical energy is converted into thermal energy due to the resistance of the wires and cannot be used to operate electrical devices. Electric resistance increases as thewires get longer. Power lines can be many kilometers long. As a result, large amounts of electricity transform into thermal energy that heats the surroundings. To reduce this wasteful conversion, a step-up transformer increases the voltage to more than 100,000 V before transmission. After transmission, a step-down transformer decreases the voltage to 120 V for consumer uses.
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Multiple Choice
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Producing Electric Current (Phys. Sci. 7.3)
Main Idea: A changing magnetic field produces an electric current in a wire loop.
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