A useful form of energy that can be converted to heat, light, and sound, electricity powers the modern world.
Atoms contain tiny particles called electrons that carry negative electrical charge. These orbit the positively charged atomic nucleus, but can become detached. Static electricity is the build-up of charge in an object. Current electricity is when charge flows.
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Current electricity
When an electric charge flows through a metal, it is called an electric current. The current is caused by the drift of negatively charged electrons through a conductor in an electrical circuit. Individual electrons actually travel very slowly, but pass electrical energy along a wire very fast.
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No current
If a conductor wire is not connected to a power supply, the free electrons within it move randomly in all directions.
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Direct current (DC)
If the wire is given energy by a battery, electrons drift toward the positive pole of the power supply. If the charge flows in one direction, it is known as direct current (DC).
Alternating current (AC)
Electrical grid electricity runs on an alternating current (AC) supply. The charge changes direction periodically, sending the electrons first one way and then the other.
Copper wire is a good conductor.
Plastic is an insulator.
Conductors and insulators
Charged particles can flow through some substances but not others.
In metals, electrons move between atoms. In solutions of salts, ions (positively charged atoms) can also flow. These substances are known as conductors. Current cannot pass through insulators, such as plastic, which have no free electrons. Semi-conductors such as silicon have atomic structures that can be altered to control the flow of electricity.
They are widely used in electronics.
Static electricity
Electricity that does not flow is called static electricity. A static charge can be produced by rubbing two materials together, transferring electrons from one to the other. Objects that gain electrons become negatively charged, while objects that lose electrons become positively charged.
Attraction and repulsion
Rubbing balloons against your hair will charge the balloons with electrons, leaving your hair positively charged. The negative charge of the balloons will attract the positive charge of your hair.
Static discharge
When ice particles within a cloud collide, they gain positive and negative charge. Lightning is an electrical discharge between positive and negative parts of a thunderstorm cloud and the ground.
Making electricity
In order to make electrons move, a source of energy is needed. This energy can be in the form of light, heat, or pressure, or it can be the energy produced by a chemical reaction. Chemical energy is the source of power in a battery-powered circuit.
Carbon anode (+)
Battery
A standard battery produces an electric current using carbon and zinc conductors and a chemical paste called an electrolyte (see pp.52-53). In a circuit, the current flows from the negative electrode (cathode) to the positive electrode (anode). Lithium batteries, which have manganese cathodes and lithium anodes, produce a stronger voltage (flow of electrons).
Zinc casing is cathode (-).
Current flows from negative to positive.
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Solar cell
Light falling onto a “photovoltaic” cell, such as a solar cell, can produce an electric current. Light knocks electrons out of their orbits around atoms. The electrons move through the cell as an electric current.
Electric circuits
An electric circuit is the path around which a current of electricity flows.
A simple circuit includes a source of electrical energy (such as a battery) and conducting wires linking components (such as switches, bulbs, and resistors) that control the flow of the current. Resistance is the degree to which materials resist the flow of current.
Switch makes or breaks circuit.
Series circuit
In a series circuit, all the components are connected one after another, so that they share the voltage of the source. If the circuit is broken, electricity ceases to flow.
Bulbs glow dimly.
Current flows from positive to negative, but electrons flow from negative to positive.
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Battery is source of electrical energy.
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Parallel circuit
A parallel circuit has two or more branches, so that each branch gets the full voltage from the source.
If the circuit is broken on one of the branches, it continues to flow through the others.
Electromagnetism
Moving a wire in a magnetic field causes a current to flow through the wire, while an electric current flowing through a wire generates a magnetic field around the wire. This creates an electromagnet-a useful device because its magnetism can be switched on and off.
Electromagnetic field
When an electric current flows through a wire, it generates rings of magnetic field lines all around it. You can see this by placing a compass near a wire carrying a current. The stronger the current, the stronger the magnetism.
Solenoid
A coil of wire carrying a current produces a stronger magnetic field than a straight wire. This coil creates a common type of electromagnet called a solenoid. Winding a solenoid around an iron core creates an even more powerful magnetic field.
Magnetic field
Direction of current
Electric motors
In an electric motor, a current flows through a coil of wire between the poles of a magnet. The magnetic field that the coil produces interacts with the field of the magnet, forcing the coil to turn. The rotating coil can be attached to a drive shaft to power a machine.
Coil rotates when current flows.
North . pole
Loops make rings of magnetic field.
Electric generators
In a generator, a current is produced by rotating a wire coil between a magnet’s poles, or by rotating a magnet while the coil is static. Generators can be big enough to power a city, or small, portable devices for supplying electricity to individuals.
Direction of current
Galvanometer registers voltage
What is an electric current? How are AC and DC currents
different? Explain with a diagram. written like a 8th grader