Electrostatics: Electric Charge
Electric Charge
- Definition: Electric charge (Q or q) is a physical property of matter that allows an object to exert an electric force on another object without touching it.
- Unit of Measurement: Measured in coulombs (C).
Key Concepts
- Electric Charge
- Exists in two types: positive (+) and negative (-) charges.
- Atoms are typically neutral, meaning they contain equal amounts of positive (protons) and negative (electrons) charges.
- Static Electricity: Accumulation of excess electric charges (positive or negative) on a body, which remain at rest.
- Electrostatics: Study of static electricity (stationary electric charges).
- Example: Rubbing a balloon on hair creates static electricity, leading to an electrostatic force greater than gravity.
Interactions of Electric Charges
- Like Charges: Repel each other (e.g., positive repels positive).
- Unlike Charges: Attract each other (e.g., positive attracts negative).
- Neutral Objects: Neutral objects are attracted to charged objects.
Conductors and Insulators
- Conductors: Materials allowing charges to move easily (e.g., metals like copper, aluminum).
- Insulators: Materials where charges do not move easily (e.g., glass, rubber, dry wood).
- Behavior of Conductors: Charge spreads out evenly on a conductor; insulators hold charges in place.
Charge Transfer and Calculation
- Process: Charges are transferred (typically electrons) through processes like friction (e.g., rubbing wool on rubber).
- Net Charge Calculation: The net charge of an object can be calculated using the formula: Q = n imes e
- Where Q = net charge (in coulombs)
- n = number of charges
- e = elementary charge of a single electron (approximately 1.6 imes 10^{-19} C).
- If an object gains electrons: Q = -n imes e (negatively charged).
- If an object loses electrons: Q = n imes e (positively charged).
Observable Phenomena
- Example of Charge Transfer: When rubber is rubbed with wool, electrons are transferred from wool (positively charged) to rubber (negatively charged).
- Excess Electrons: An electroscope with a charge of -1.44 imes 10^{-16} C can be analyzed to find the number of excess electrons using the aforementioned formula.
Summary of Key Points
- Electric charge is a cornerstone of electrostatics, explaining various phenomena like static cling and lightning.
- The conservation of charge states that charges are neither created nor destroyed, only transferred.
- Understanding charge and its properties is foundational to modern technology, such as batteries and electronics.