1. A coil is formed by winding 250 turns of insulated 16-gauge copper wire, that has a diameter d = 1.3 mm, in a single layer on a cylindrical form of radius 12 cm. What is the resistance of the coil? Neglect the thickness of the insulation and the resistivity of copper is = 1.69 × 10−8 Ω ∙ m.

2.39 Ω

Explanation:

Given that

Number of winnings on the coil, = 250 turns

Radius if the copper wire, r(c) = 1.3/2 = 0.65 mm

Radius of single cylinder layer, R = 12 cm

Length of the cylinderical coil, L = 250 * 2π * 12 = 188.4 m

Resistivity of copper, ρ = 1.69*10^-8 Ωm

Area is πr(c)², which is

A = 3.142 * (0.65*10^-3)²

A = 3.142 * 4.225*10^-7

A = 1.33*10^-6 m²

The formula for resistance is given as

R = ρ.L/A, if we substitute, we have

R = (1.69*10^-8 * 188.4) / 1.33*10^-6

R = 3.18*10^-6 / 1.33*10^-6

R = 2.39 Ω.

Therefore, the resistance is 2.39 Ω

answer: option c. i.e. electric current flowing “downhill” from the negative electrode to the positive electrode in a battery

explanation:

the water analogy to the circuits define the pipes (water flows) to the electric current. now, we know that the electric current flows from the positive terminal to the circuit (as shown in the diagram attached).

hence, option c is the correct answer.