# physics

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Два равных отрицательных заряда по 9 нКл каждый находятся в воде (ε=81) на расстоянии 8 см друга от друга. Определить напряженность и потенциал поля в точке, расположенной на расстоянии 5 см от зарядов.

Two equal negative charge on 9 nC each are in the water (ε = 81) at a distance of 8 inches apart. Determine the strength and potential of the field at a point located at a distance of 5 cm from the charges

• physics - ,

8 cm apart I assume

Do the potential first. It is easy because you can add potentials due to each charge without doing any geometry.
V = 2 * [ q/ (4 pi eo r ) ]

for each E field you must first find the E vector away from each charge and multiply by the cosine of the angle between that and the direction perpendicular to the line between the charges
Draw the triangle
base 8, legs 5
half the base = 4
right triangles, 3, 4 ,5
cos A = 3/5
so
E = 2 [ q/(4 pi eo r^2)](3/5)

• physics - ,

explanation on how to use Snell's law for refraction to calculate the refrection

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A ball of mass 8kg fall from rest from a height of 100m calculate the k.E energy after falling with a distance of 30m