# Electric Fields (Part 1 of 2)

Part 2 of Electric Fields is here: Electric Fields (Part 2 of 2)

- Like charges repel
- Opposite charges attract

## Coulomb’s Law (Inverse Square Law)

The magnitude of the force between two charges is proportional to the product of the magnitude of the charges.

F_{e} = K q_{1} q_{2} / r^{2}

q

_{1}× q_{2}= c^{2}, after multiplicationr

^{2}= m^{2}| number | – denotes the numbers absolute value – ignoring negative notation, eg. | -3.124 | = 3.124

K

_{e}= approx. 9×10^{9}Nm^{2}/c^{2}

**Example:**

Q1 = 5×10^{-3} c

Q2 = -1×10^{-1} c

∴ F_{e} = 9×10^{9} Nm^{2}/c^{2} | (5×10^{-3} c) (-1×10^{-1} c) | / (0.5 m)^{2}

F_{e} = 45×10^{5} N~~m~~/ 0.25 ^{2} ~~m~~^{2}

**F _{e} = 1.8×10^{7} N** – Attractive force

Sometimes the r

^{2}is denoted as d^{2}– for distance

## Conservation of Charge Law

^{*}∑_{q} = Constant

_{*}= No net change incoming or outgoing∑ = Sum of all

q = charge (c)

For example, a closed box:

- A = +2 c
- B = +5 c
- C = -3 c

The sum of all charges = + 4 c, which remains constant if the box is closed.

These charges may move, collide, exchange charges – the point is: even if the particles change after x amount of time; the **charge** will still be the same.

To continue with the above box, after 1 hour:

- A = +1 c
- B = -7 c
- C = ?

A + B + C = + 4 c

1 + (-7) + C = + 4 c

∴ C = + 10 c

This law is also true in forms of decaying particles

## Recommended Reading for Physics

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