Two coaxial circular coils of radius r = 15 cm, each carrying 4.0 a in the same direction, are positioned a distance d = 20 cm apart, as shown in the figure. calculate the magnitude of the magnetic field halfway between the coils along the line connecting their centers.

An object with initial temperature 130 ∘ f is submerged in large tank of water whose temperature is 50 ∘ f . find a formula for f ( t ) , the temperature of the object after t minutes, if the cooling constant is k = − 0.2 . remember newton's law of cooling (the rate of change of temperature with respect to time is equal to k times the difference between the temperature of the object and the surrounding temperature) ! : )