You have the simpliest circuit in the world:
A lightbulb and a switch.
You turn it on for an hour, then you switch it on and off for an hour.
Which takes more energy and why?
I was arguing about this with my friends for like 3 hours. My logic is that if you switch it on and off regularly it takes half of the energy needed to be lit for an hour. They said that a single click to light it needs more energy. It's an analogy to car engine. You need some fuel to turn it on but it takes less fuel when it's on.
Which is right and why?
If the circuit is using direct current, you're correct.
If alternating current is used, They are correct that it takes more energy, but for the wrong reason.
It has to do with just how many Joules/coulomb you can squeeze out of a modern-day battery source.
Hope that helps.
You are right and they are wrong. They are probably confused because they heard that will wear out the bulb faster (which is true), but it won't use more energy.
You can see that's the case even without a current meter. If switching it on used more energy, that energy would still have to go somewhere, ie light or heat. It doesn't create a bright flash of light, so that leaves heat. Does the bulb heat up instantly in a flash, burning your hand if you are touching the bulb when it turns on? No, it starts out cool and takes several seconds to warm up.
>single click to light it needs more energy
In principle, yes, but only for a fraction of a second. The reason is that the initial current is much higher than the nominal current which produces I^2R losses in the wiring. The initial power of a 230V/100W lightbulb is about 1.5kW. That's why they light up so fast and always blow at switch-on.