GED Science Practice Test: Electric Current
Read the following passage and answer the following question:
An electric current is a flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire. Electric current is measured in units called amperes, or amps, which is the flow of electric charges through a surface at the rate of one coulomb per second.
Electrical current is the flow of electrons from negative to positive. If you remember that opposite charges attract, this makes sense. Electrons, which have a negative charge, move away from negatively charged things, and move toward positively charged things. If you picture an electrical circuit, a closed path around which electrons travel, this direction for electrical current will make sense.
In this diagram, a battery changes the chemical energy within it to electrical energy. Electrons are considered to flow out of the negative end of the battery, around the wire, and toward the positive end of the battery, to which the electrons are attracted. Though we know that electrical current involves the flow of electrons, this was not always known. When scientists first discovered electricity, they thought that positive charges flowed the opposite direction in an electrical circuit. While the end result is the same, we now have two different ways of talking about electrical current: by electron flow or conventional current. You find both of these methods used in textbooks and wiring diagrams. The two conventions for describing electrical current are pictured below:
Through inefficient energy transformations, electric currents convert much of their energy to unuseful heat. This is why energy lightbulbs such as fluorescents and LEDS are considered more efficient—they do not “lose” as much energy through transformation to heat. Electric currents can also create, or induce, magnetic fields. We will turn our attention to magnetic fields.
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In an electrical circuit, electrons are flowing counterclockwise. Which direction is the current moving in?
Which of the following are necessary to create an electrical circuit?