What determines the rate at which energy is delivered by a current

An electric iron of resistance 20 W takes a current of 5 A. Calculate the heat developed in 30 s.

Compute the heat generated while transferring 96000 Coulomb of charge in one hour through a potential difference of 50 V.

Why does the cord of an electric heater not glow while the heating element does?

What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 4 Ω, 8 Ω, 12 Ω, 24 Ω?

How can three resistors of resistances 2 Ω, 3 Ω and 6 Ω be connected to give a total resistance of (a) 4 Ω, (b) 1 Ω