# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
V
valence electron: An electron in the outer shell of an atom.
valency: This is short for ‘electrovalency’.
vernal equinox: The intersection of the ecliptic and celestial equator, which the Sun passes each year on 22 March.
virtual image: An image that is produced in a mirror or lens or other transparent material where light does not actually pass through the image. A virtual image cannot be seen on a screen.
viscosity: A measure of how well a liquid flows.
volcanic rock: Extrusive igneous rock.
volcano: A conical mountain formed around a vent as a result of the eruption of lava and pyroclastic materials.
volt (V): The unit for voltage. 1 V represents 1 J (joule) per coulomb of charge. Therefore, a 9 V battery supplies each charge with 9 J.
voltage: The amount of electrical energy given to each coulomb by a battery in an electric circuit. Voltage also represents the amount of electrical energy per coulomb transformed at a load in an electric circuit. Voltage is also called ‘potential difference’ and is measured in volts.
voltaic cell: An electrochemical cell.
voltmeter: A device that measures voltage. It must be placed across two parts of an electric circuit. That is, it must form a parallel branch in an electric circuit over the load or battery for which the voltage is unknown.