Electric Fields (Part 1 of 2)

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

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• 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 q₁ q₂ / r²

q₁ × q₂ = c², after multiplication

r² = m²

| number | – denotes the numbers absolute value – ignoring negative notation, eg. | -3.124 | = 3.124

K_e = approx. 9×10⁹ Nm²/c²

Example:

Q1 = 5×10^-3 c

Q2 = -1×10^-1 c

∴ F_e = 9×10⁹ Nm²/c² | (5×10^-3 c) (-1×10^-1 c) | / (0.5 m)²

F_e = 45×10⁵ Nm² / 0.25 m²

F_e = 1.8×10⁷ N – Attractive force

Sometimes the r² is denoted as d² – 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

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