What is the power consumption of 40 watt fluorescent tube?

You probably Worded your question wrong, since the answer would be 40w. But I'll work out the charge to run it for you.

I am working your questions using the MELBOURNE, Australia power tariff (charge) which is 17.000c per kw/h.

It takes roughly 25 hours for your 40w fluoro tube to consume 1 kilowatt of power, so the power consumption per hour would be around 0.0068 cents an hour.

Please take note of other amounts of electricity that have to be used in order to fire up your tube though, as some starter capacitors can use a big amount of energy (this is the reason why it is not recommended to use fluoro bulbs on 12v/24v - 240v/110v inverters). So basically, if you are going to be out of the room for less than 1 hour, leave it on.