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Energy in capacitors: An ideal parallel-plate capacitor consists of a set of two parallel plates of area A separated by a very small distance d. When this capacitor is connected to a battery that maintains a constant potential difference between the plates, the energy stored in the capacitor is U0. If the separation between the plates is doubled, how much energy is stored in the capacitor?

Power: A certain electric furnace consumes 24 kW when it is connected to a 240 V line. What is the resistance of the furnace?

Electric field of a single point-charge: A metal sphere of radius 10 cm carries a charge of +2.0

Potential due to point-charges: A +4.0

Current density: A proton beam that carries a total current of 1.3 mA has 10.0 mm diameter. The current density in the proton beam increases linearly with distance from the center. This is expressed mathematically as J(r) = J0 (r/R), where R is the radius of the beam and J0 is the current density at the edge. Determine the value of J0.

Internal battery resistance: When a 20.0-ohm resistor is connected across the terminals of a 12.0 V battery, the voltage across the terminals of the battery falls by 0.300 V. What is the internal resistance of this battery?

Coulomb’s law: A + 7.00

Equipotential surfaces: A negative charge is moved from point A to point B along an equipotential surface. Which of the following statements must be true for this case?

Internal battery resistance: What is the maximum current that can be drawn from a 1.50 V battery with an internal resistance of 0.30 ohm?

Parallel-plate capacitors: Each plate of a parallel-plate air-filled capacitor has an area of  0.0020 m2, and the separation of the plates is 0.020 mm An electric field of 3.9 x 106 V/m is present between the plates. What is the surface charge density on the plates? (