What's the question I don't get it?
Pumice rocks are formed due to the air that is trapped in
between the rocks, a body of magma spurting out with dissolved gas under
pressure. As the magma cracks through the Earth’s surface, the sudden pressure
drop causes the gas to come out of the solution. The flash of gas form the vent
slices the magma and blows it out as a molten lather. The lather hastily
solidifies as it flies into the air and falls back to Earth as pieces of
pumice.
D
B
those are the correct answers
Answer:
As you haven't explained what measurements you took before solving this problem, I will explain the general procedure to evaluate the efficiency of a kettle. I hope it helps you. I´ll send an attachement file with the full answer, since I couldn't write it here.
I assume that the material that is going to be heated in the kettle is water.
1- You have to boil water in it and take the time it takes to its boiling point (in seconds).
2- You have to evaluate the amount of energy the water absorbed Q with the efficiency formula which I explain in the attachement file.
3- Divide Q by the time it took to bring the water to boiling so you can have the power it consumed.
4- You divide the last value you obtained by the Kettles's power rating.
5- Multiply the last value by 100 to obtain a percentage value of efficiency.
Explanation:
Efficiency is the ration of a machine's useful work, in this case how much energy the water absorbed to get to its boiling point divided by the time it took to get to this point, and the total energy expended, in this case the kettles's power rating.