For a school project, I have to make a mug heater which draws its power from a computer's USB port, such as this one. I don't mean one that boils the tea, but one that keeps it warm-ish, at at least 40 degrees. Apparently, a USB port can give 500 mA at 5 Volts, which gives me at most 2.5 W. At first, I thought this wasn't nearly enough for a heater, but then I decided to experiment.
I decided to forget the rest of the circuit and pretended that the heating element could take all of the 500 mA. The best thing I could get my hands on was nichrome wire, and I worked out that to get a resistance of 10 Ω (to use all of the available power), I needed approximately 0.6m of swg 32. I experimented, and at 5 V and 500 mA, there was no heat produced whatsoever; as in, I could even touch the wire without feeling heat, let alone feel the heat above it.
How would I go about doing this? I know for a fact that this is possible (see the first link).
EDIT: Yes, there was current flowing (I used an ammeter), and I did coil the wire up.