電源 and 電力: the supply switched and the power calculated
Compare machine and backup 電源 with the 電力 used by a model or calculated for an assumed outage. Identify a shutdown request, an actual switch after an outage, and the object of a power calculation.
電源: power turned off or switched
電源, read でんげん, refers to a power supply or power. 「作業が終わったら機械の電源を切ってください。」 asks for the machine's power to be turned off when the work is complete. It does not report that the power has already been turned off.
「停電の後、予備の電源に切り替えた。」 says there was a switch to backup power after the outage. Read 切り替えた together with 予備の電源, the supply switched to.
電力: power used or calculated
電力, read でんりょく, means electric power. 「この模型はわずかな電力で動く。」 says the model runs on very little electric power. わずかな describes the amount without providing an actual numerical value.
「停電を想定して必要な電力を計算した。」 says the power needed in the event of an outage was calculated. Calculation is the completed action; the outage is the scenario expressed by 想定して.
The switch target and the calculation target
In 予備の電源に切り替える, the backup supply is the switch target. In 必要な電力を計算する, required electric power is the calculation target. The examples give these related electrical words different objects and actions.
Keep the actual switch after an outage separate from the calculation based on an assumed outage. A calculation does not establish that sufficient power was secured. Likewise, the shutdown request should not be read as a report of completed shutdown.
What is switched in 予備の電源に切り替える, and what is calculated in 必要な電力を計算する?
Show the answer and why
電源 names the backup supply switched to, while 電力 names the required power calculated. The switch after an outage is a past action. The other example reports a calculation for an assumed outage, not proof of an actual outage or a secured supply.