Charges between clouds or between a cloud and the ground produce atmospheric electrical discharges or lightning. The flow of electricity from one discharge point to another also produces a sound wave heard as thunder.

An electroscope is used to detect the presence of electric charges, to determine whether these charges are positive or negative, and to measure and indicate their intensity. This schematic drawing shows the basic parts of the device: (a, a_) are thin leaves of metal foil, suspended from (b), a metal support; (c) is a glass container, while (d) is a knob that collects electric charges. Electric charges (either positive or negative) are conducted to the leaves at the bottom via the metal support. Because like charges repel one another, the leaves fly apart. The amount of the charge is calculated by measuring the distance the leaves are forced apart.

Electric current discharges between two electrical conductors (the metal nails). The voltage of the electric discharge must be large enough to jump across the nonconductive medium (the air or vacuum) between the conductors. If the voltage is too low the electricity will not flow.

Two rods that carry the same kind of charge repel each other. To observe this, obtain two rods that are made of the same kind of material (glass stirring rods, for example). Rub both rods in the same way (with a piece of silk, for example). If they are made of the same material and have been rubbed in the same way, the rods should carry the same kind of charge. Hang one rod from a thread so that it is free to rotate. Bring the other rod near. The first rod should rotate away from the second, demonstrating that like charges repel. If the rods had different kinds of charges, the first rod would rotate toward the second, demonstrating that unlike charges attract.

Coulomb used a torsion balance to investigate electrostatic forces. A quantity of charge q₁ is rubbed on a fixed sphere. A second charge q₂ is rubbed on a sphere on the end of a suspended rod that is free to rotate. The force exerted by q₁ on q₂ twists the rod and suspending fiber. Turning the suspension head twists the fiber back so that the two spheres stay the same distance apart. The magnitude of the force is indicated by the angle through which the suspension head is turned. Coulomb found that the force exerted by one charge on another was directly proportional to the magnitudes of both charges (q₁q₂). The bigger the magnitudes, the bigger the force. He also found that force was inversely proportional to the square of the distance, r, between the charged spheres. The smaller the distance, the bigger the force. This is known as Coulomb’s Law: F = q₁q₂/r²

A charged object will induce a charge on a nearby conductor. In this example, a negatively charged rod pushes some of the negatively charged electrons to the far side of a nearby copper sphere because like charges repel each other. The positive charges that remain on the near side of the sphere are attracted to the rod. If the sphere is grounded so that the electrons can escape altogether, the charge on the sphere will remain if the rod is removed.

This illustration shows the electric circuit used in a simple flashlight. Current, provided by a battery, flows through a wire, into a blub, and through another wire back to the battery. As the current flows through a tiny wire inside the bulb, called a filament, it heats the filament to such a high temperature that the filament glows.

Electric circuits with only a single path for electricity to flow along are called series circuits. Electric circuits with multiple pathways for electricity to flow along are called parallel circuits. A circuit’s total resistance to the flow of electricity is calculated differently for series circuits than it is for parallel circuits.

Electric lines of force indicate the direction in which a positive test charge would move if it were placed in an electric field. The diagram on the left shows lines of force for two positive charges that repel each other. A positive test charge would be pushed away from both charges. The diagram on the right shows lines of force for two unlike charges that attract each other. A positive test charge would be pushed away from the positive charge and toward the negative charge.

You can visualize the magnetic field created by an electric current flowing through a wire using your right hand. Point your thumb in the direction the current is flowing and curl your fingers as if making a fist. The magnetic field curves around the wire in the same direction that your fingers curl around the axis defined by your thumb.