Two equal positive charges q_1 = q_2 = 2.0μ∁ are located at x= 0, y=0.30m and x=0, y=-0.30m, respectively. What are the magnitude and direction of the total electric force that q_1 and q_2 exert on the third charge Q = 4.0μ∁ at x = 0.40m, y = 0?

It is really hard for me right know

Antireflective coatings on solar cells are often made by applying a thin film of silicon nitride (sinx), which has an index of refractive of 1.2, on the top of the silicon solar cell, which has a refractive index of about 3.5. however, the sun emits radiation of various wavelengths which the solar cell absorbs, and the antireflective coating can only absolutely minimize the reflection of one of these wavelengths. the coating thickness is chosen to reduce the reflection of green/yellow light (e = 2.2 ev), which is the most intense color in the solar spectrum (shown below). which of the following coatings would minimize reflection of green/yellow light? the answer is 820 nm how? what is the angular width of the central maximum of an electron traveling at 2 x 108 m/s going through a single slit of width 1 mm.

The voltage applied across a given parallel-plate capacitor is doubled. how is the energy stored in the capacitor affected?