Tại hai đỉnh của hình vuông ABCD cạnh a = 3 cm có đặt hai điện tích điểm q1 = -q và q2 = +q. Tính q và cường độ điện trường tại đỉnh A. Cho biết điện thế tại A là 8500 V

A248-g piece of copper is dropped into 390 ml of water at 22.6 °c. the final temperature of the water was measured as 39.9 °c. calculate the initial temperature of the piece of copper. assume that all heat transfer occurs between the copper and the water. remember, the density of water is 1.0 g/m

Because air contracts as it cools, the air pressure inside a freezer is typically lower than on the outside. why do ice cubes inside a freezer tend to shrink over time? a. the ice dissolves oxygen from the air, forming a denser crystalline matrix.b. the ice reacts chemically with carbon dioxide in the air, forming gaseous carbon compounds.c. the ice melts, and then the liquid freezes as ice crystals on the bottom of the freezer.d. the ice sublimes, and then the water vapor deposits as ice crystals on the sides of the freezer.

Suppose a wire with a current is pushed upward by a magnetic field. how would the wire move if the direction of the current reversed? explain your answer.