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Concept

The Nature of Electric Charge

Explains polarity, conductors vs insulators, and basic charge properties.

Have you ever felt a shock from a car door or seen lightning? These phenomena are due to electric charge. When certain insulating materials are rubbed together (like a glass rod and silk), they transfer charge, creating static electricity.

Historically, Benjamin Franklin named the two resulting states of electrification positive and negative. Like charges repel, and unlike charges attract.

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Diagram

Electron Transfer

Visual showing electron transfer between glass rod and silk.

clean scientific diagram, pastel color palette, elegant typography, precise labeling, translucent layers for cross-sections, white background, soft shadows. A glass rod being rubbed with a silk cloth, showing negatively charged electrons transferring from the glass rod to the silk, leaving the glass rod with a net positive charge and the silk with a net negative charge.

Click to zoom

Rubbing an insulator transfers electrons, creating opposite polarities on each material. Charge is conserved; no new charge is created.

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Quantization of Charge

Formula card for q = ne.

q = n e

Charge exists in whole-number multiples of elementary charge.

q

Total Net Charge

Charge on the object

n

Integer

\pm 1, \pm 2, \pm 3...

e

Elementary Charge

1.602 \times 1 0^{- 19}

C

Note: Electrons carry negative charge

(- e)

, while protons carry positive charge

(+ e)

. Charge looks continuous at large scales, but is actually made of tiny fixed units.

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Worked Example

Time to Accumulate 1 C

Calculates time to transfer 1 Coulomb if 10^9 electrons move per second.

Problem

If $10^9$ electrons move out of a body to another body every second, how much time is required to get a total charge of $1$ C on the other body?

Given:

Rate of transfer: $10^9$ electrons/second
Elementary charge $e$ : $1.6 \times 10^{-19}$ C
Target charge: $1$ C

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Worked Example

Charge in a Cup of Water

Calculates total positive and negative charge in 250g of water.

Problem

How much positive and negative charge is there in a cup of water?

Given:

Mass of one cup of water: assume $m = 250$ g
Molecular mass of water ( $\text{H}_2\text{O}$ ): $M = 18$ g/mol
Avogadro's number: $N_A = 6.02 \times 10^{23} \text{ molecules/mol}$

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Worksheet

Charge of Specific Atoms

Calculate the total charge of a given number of particles.

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To find the total positive charge in 1 mole of Helium gas, we first determine the number of atoms. By definition, one mole of Helium contains approximately $6.02 \times 10^{23}$ atoms. Each Helium atom contains exactly protons in its nucleus.

The magnitude of the positive charge contributed by a single proton is the elementary charge $e$ , which is $1.6 \times 10^{-19} \text{ C}$ . We can find the total positive charge by multiplying the total number of atoms by the number of protons per atom and the elementary charge.

Total positive charge = $(6.02 \times 10^{23}) \times$ $\times (1.6 \times 10^{-19} \text{ C})$ .

Evaluating this expression gives a total positive charge of roughly $1.93 \times 10^{5} \text{ C}$ .