A 12 V car ignition coil has an inductance of 10 mH and resistance of 2 Ω (so its equivalent circuit is a 10 mH inductor in series with a 2 Ω resistor). Calculate how long it takes the current to build up to 95% of its maximum value after a 12 V battery is connected to the coil?

t = 0.01497 s

Explanation:

This series RL circuit is described by the expression

        I = I₀ (1 - )

where τ = L / R

Let's clear

         I / I₀ = 1 - e^{-t/\tau }

         e^{-t/\tau  } = 1 - I / I₀

          t /τ = ln (1- I/I₀)

In our case

          I / I₀ = 0.95

         -t /τ = ln (1 -0.95)

         -t /τ = -2.9957

          t = 2.9957 τ = 2.9957 (10 10⁻³ / 2)

          t = 0.01497 s

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.