2. (2% for each blank, 6% in total, 本題計算過程不計分)A very simple electric circuit is shown in Fig. 2. Please find I₁ = __(2a)__, I₂ = __(2b)__ and I₃ = __(2c)__.

6. (7%, 本題計算過程須計分) Two spherical conductors of radii r₁ and r₂ are separated by a distance much greater than the radius of either sphere. The spheres are connected by a conducting wire as shown in Fig. 4. The charges on the spheres in equilibrium are q₁ and q₂, respectively, and they are uniformly charged. Find the ratio of the magnitude of the electric field at the surface of the sphere 1 to the one of the sphere 2 is__ (6a) (3%)__. Please use the meaning of the ratio to explain the principle of a lightning rod (避雷計). Your explanation: __(6b) (4%)__

2. (2% for each blank, 6% in total, 本題計算過程不計分)

A very simple electric circuit is shown in Fig. 2. Please find I₁ = (2a), I₂ = (2b) and I₃ = (2c).

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