Fish tank water must be kept at at a particular pH level so the fish stay healthy. What is the best way you protect the water from becoming too acidic or too basic?

[A] Fill the tank with colored water
[B] Put pH paper on the tank
[C] Add acid to the water
[D] Add a buffer to the water

In a heat engine if 1000 j of heat enters the system the piston does 500 j of work, what is the final internal energy of the system if the initial energy was 2000 j ?

The diagram shows a series of volcanic island and a hot spot determine the direction of movement of the tectonic plate that for the island

Along wire carrying a 4.2 a current perpendicular to the xy-plane intersects the x-axis at x=−1.7cm. a second, parallel wire carrying a 3.0 a current intersects the x-axis at x=+1.7cm. part a at what point on the x-axis is the magnetic field zero if the two currents are in the same direction? express your answer to two significant figures and include the appropriate units.