An electric kettle rated 1.5kW is used for 4min to heat water. An immersion rod rated 750W is used for 8min to heat the same amount of water. Which one of the following statements about the electrical energy supplied is correct?
a) The kettle supplies twice as much energy as the immersion rod.
b) The energies cannot be compared without knowing the supply voltage.
c) Both devices supply the same amount of energy.
d) The kettle supplies four times as much energy as the immersion rod.