# Electric Field - Video Tutorials & Practice Problems

## Intro to Electric Fields

A 1.5μC charge, with a mass of 50g, is in the presence of an electric field that perfectly balances its gravity. What magnitude does the electric field need to be, and in what direction does it need to point?

^{−7}downwards

^{2}upwards

^{4}upwards

^{5}upwards

## Electric Field due to a Point Charge

## Zero Electric Field due to Two Charges

If two equal charges are separated by some distance, they form an electric dipole. Find the electric field at the center of an electric dipole, given by the point P in the following figure, formed by a 1C and a −1C charge separated by 1 cm.

^{14}N/C

^{12}N/C

^{14}N/C

^{14}N/C

## Electric Field Above Two Charges (Triangle)

4 charges are arranged as shown in the following figure. Find the magnitude of the electric field at the center of the arrangement, indicated by the point P.

8.99×10^{9} N/C

1.21×10^{10} N/C

3.24×10^{10} N/C

8.09×10^{10} N/C

1.94×10^{11} N/C

## Balancing a Pendulum in Electric Field

In the following figure, a mass m is balanced such that its tether is perfectly horizontal. If the mass is m and the angle of the electric field is θ, what is the magnitude of the electric field, E, expressed in terms of m, q, and θ?

Ε = qmg/sinθ

Ε = T/(q cosθ)

E = q sinθ/(mg)

Ε = mg/(q sinθ)

E = mg/(q cosθ)

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