Definition
A unit of electrical energy equal to the work done by one watt of power acting for one second. One watt-second equals one joule.
Plain English
A small unit of energy that measures how much electrical work is done when one watt is used for one second.
Context Anchor
Seen in aircraft electrical-system discussions when a manual describes how much energy is used or stored.
Derivation
Formed from 'watt' (the unit of power, named after engineer James Watt) and 'second' (the unit of time). Multiplying power by time gives energy, so a watt acting for one second is one watt-second of energy delivered.
Why Pilots Care
Strobe lights, capacitor-discharge ignition systems, and emergency power devices are often rated in watt-seconds. Knowing the rating helps pilots and technicians understand the energy stored or delivered per pulse.
Grounding Statement
If a 1-watt light stayed on for 1 second, it would use 1 watt-second of energy.
Intuition Check
Do not read watt-second as just another way to say watt. A watt is a rate; a watt-second is an amount of energy.
Example Sentence 1
The aircraft's anti-collision strobe is rated at 20 watt-seconds per flash.
Example Sentence 2
Technicians checked the total energy stored in the aircraft battery by measuring watt-seconds delivered during the test discharge.