8. In a circuit, a difference of potential can exist between two points on the circuit, but usually, the difference in potential is generally measured against the metal chassis on which the
parts of the circuit are mounted. This reference is called the:
A. EMF
B. Ground potential
C. Voltage
D. Relative Charge.

Identify the correct relation showing that the radius r of the orbit of a moon of a given planet can be determined from the radius r of the planet, the acceleration of gravity at the surface of the planet, and the time τ required by the moon to complete one full revolution about the planet. determine the acceleration of gravity at the surface of the planet jupiter knowing that r = 71 492 km and that t= 3.551 days and r= 670.9 × 10^3 km for its moon europa.