Voltage and potential difference

The volt is named in honor of Alessandro Volta, who invented the first chemical battery in 1800. Volta discovered how to convert chemical energy into electrical energy by alternating plates of two different metals in a dilute acid or salt solution. In practical terms, a volt (V) tells you the amount of electrical power carried by one ampere of current. For example, each ampere of current flowing out of a 12 V battery carries 12 W of electrical power. The same ampere of current flowing out of a 120 V wall socket carries 120 W of electrical power. Voltage in a circuit is measured with a voltmeter. Read the text aloud Show More on Volta's invention of the battery
Analogy between the concept of water flowing and electric current
Current is what flows and does work. Voltage, in contrast, is what causes current to flow. The idea of water pressure in pipes makes a good analogy for voltage. A pressure difference causes water to flow in a pipe, and voltage causes electric current to flow in a wire. If there is no voltage, then no current flows. You can connect a loop of wire to a bulb in a closed circuit but current will not flow unless there is a battery or some other voltage source in the circuit. Current only flows in response to a voltage difference. Read the text aloud
The term potential difference is another way to describe voltage. A 1.5 V battery has a potential difference of 1.5 V between its positive and negative terminals. Electrical potential difference is analogous to the difference in potential energy for water at two different heights. Read the text aloud
Voltage can only be measured between two points, such as the two terminals of a battery. If we measure the voltage of an ordinary 1.5 V battery from the flat (−) end to the slightly protruding (+) end, we would record a voltage gain of +1.5 V, indicating an increase in electric potential. If we swapped the leads on our voltmeter so that we measured from the + to the − end of the battery, we would measure a voltage drop of −1.5 V. When we say that a battery is “1.5 V” we are implicitly choosing the negative end of the battery to be our reference of 0 V. Read the text aloud Show What does <i>nominal</i> mean here?
By convention, electric current flows from high (more positive) potential to low (more negative) potential. In circuit diagrams, an arrow is often used to indicate the direction of current flow. “Conventional” current flows out of the positive terminal of a battery and returns to the negative terminal. In most conductors it is actually negative electrons that move to carry electric current. Because electrons are negatively charged, the electron flow is opposite from the direction of conventional current. Read the text aloud
Jermaine connects a resistor across a battery. As the current passes through the battery, is this a voltage gain or a voltage drop? As the current passes through the resistor, is this a voltage gain or a voltage drop? Show

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