"Dave Liquorice" wrote in message
. 1...

Just looked at the rating panel on our fairly recent Category E (800W
output) microwave. Input power is 1.24kW so over a 1/3rd of the input
power goes has waste heat.

Kettles must be far better or they would melt, not having forced
cooling...

They have water cooling though, and a fair heat capacity.

Method:
Cool kettle using several litres of tap water, measure
1 tea-cup of tap water into kettle, and time until bubbling
Cool kettle using several litres of tap water, measure
2 tea-cups of tap water into kettle, and time until bubbling

Results: 60s and 90s.

Conclusion: a microwave is just about as efficient for one
cup of tea, but slower.