Electric Charge ⚡️
What’s going on when things “spark” or crackle?
Static electricity shows up any time charges build up on objects that don’t let them move away easily. Removing a sweater in dry weather or seeing a lightning bolt are everyday and grand-scale examples of the same phenomenon — electric charges suddenly finding a path to redistribute. :contentReference[oaicite:0]{index=0}
Two kinds of charge & their golden rule 🔄
- Like charges repel, unlike charges attract. Place two glass rods (both rubbed with silk) near each other and they push apart; bring a glass rod next to the silk and they pull together. :contentReference[oaicite:1]{index=1}
- The property distinguishing the two varieties is called polarity.
- By convention, the charge on a glass rod (or cat’s fur) is positive (+); the charge on silk or plastic is negative (−). :contentReference[oaicite:2]{index=2}
How objects get charged ✨
Rubbing transfers a few loose electrons from one surface to another. If electrons leave an object, it becomes positively charged; if it gains extra electrons, it becomes negatively charged. No charge is created or destroyed — only shuffled around, and the amount moved is tiny compared with the total number of electrons in either object. :contentReference[oaicite:3]{index=3}
Detecting charge: the gold-leaf electroscope 🔍
Touch a charged body to the metal knob and identical charges spread to two thin gold leaves. Their mutual repulsion makes the leaves diverge; the wider the separation, the greater the charge. :contentReference[oaicite:4]{index=4}
Conductors vs. Insulators 📋
| Conductors 🔌 | Insulators 🛡️ |
|---|---|
| Electrons move freely e.g., metals, the human body, Earth :contentReference[oaicite:5]{index=5} | Electrons are locked in place e.g., glass, plastic, wood, nylon :contentReference[oaicite:6]{index=6} |
| Added charge spreads quickly over the whole surface. | Added charge stays where it was deposited. |
Why this matters 🧐
Every force that glues molecules, keeps solids intact, or lets a comb lift little paper bits after a few strokes through dry hair is electrical at its core. Understanding charge is the first step toward grasping electric forces, fields, and circuits. :contentReference[oaicite:7]{index=7}
Important Concepts for NEET 🎯
- Polarity principle: like charges repel, unlike charges attract.
- Charge transfer via electrons: frictional charging moves electrons, not protons.
- Gold-leaf electroscope: classic detector for sign and magnitude of charge.
- Conductor vs. insulator behavior: mobility of charge carriers determines charge distribution.
