NIS – PHYSICAL SCIENCE

1. NIS – PHYSICAL SCIENCE Lecture 50 – Lecture 51 Electric Charge OzgurUnal

2. Are you familiar with socks • clinging together when • removed from the dryer? Electric Charge • This is caused by static charges • on the socks  What is charge? • Let’s remember the structure of atom! • Protons have positive charge. • Electrons have negative charge. • Neutrons are neutral. • Objects with equal amounts of electrons • and protons are neutral.

3. Electrons are bound to the nucleus, but sometimes not so strongly. • Electrons might sometimes move from one object to another. • When this happens objects become charged. Transferring Charge • Example: Walking on a carpet with your shoes • As the soles of your shoes rub against the carpet, the electrons in the carpet are transferred to your shoes. • Carpet loses electrons  positively charged • Shoes gain electron  negatively charged • Charges accumulate on the carpet and the shoes • The accumulation of excess electric charge on an object is called static electricity.

4. When an object becomes charged, charge is neither created nor destroyed  it is transferred • According to the law of conservation of charge, charge can be transferred from object to object, but it cannot be created or destroyed. Conservation of Charge

5. Clothes cling together when removed from dryer, because they attract each other. • This attraction is due to the attraction of charges on the clothes. Coulomb’s Law • Coulomb’s Law describes the force between charges: • Fe = k Q1*Q2 / r2 • Fe: Electrostatic force • k: constant • Q1, Q2: Amount of charges • r: Distance between charges • Identify the similarities between law of gravity. • http://webphysics.davidson.edu/physlet_resources/bu_semester2/c01_charge.html • http://webphysics.davidson.edu/physlet_resources/bu_semester2/c01_magnitude.html

6. Like charges repel each other • Unlike charges attract each other • As the distance increases, the magnitude of the electrostatic (Coulomb) force decreases • As the amount of charge increases, the magnitude of the electrostatic (Coulomb) force increases Coulomb’s Law

7. An electric field surrounds every electric charge • When a second charge is brought to this electric field, it is either attracted or repelled. Electric Fields

8. The space within and between atoms on any object is quite big. • Atoms and objects are mostly empty space. • Given this, how come you cannot pass through the objects? Observable Effects of Electric Forces

9. What material is used inside electric cables? • A material in which electrons are able to move easily is a conductor. • Example: Metals Conductors and Insulators • Why are electric cables are coated with plastic? • A material in which electrons are not able to move easily is an insulator. • Electrons are tightly held to atoms in insulators. • Example: Plastic, wood, rubber, glass etc.

10. How exactly the socks are able to cling to each other after they have been dried in the drier? Charging Objects • As the socks tumble in the drier, there occurs a charge transfer between the socks. • One of the socks lose electrons (+ly charged), and the other gains these electrons (-ly charged). • The process of transferring charge by touching or rubbing is called charging by contact.

11. Objects can be charged without rubbing or touching. • Example: Charging Objects • The rearrangement of electrons on a neutral object caused by a nearby charged object is called charging by induction.

12. Lightning, Thunder and Grounding: • Go over Figure 8!! Charging Objects

13. The presence of electric charges can be detected by an electroscope. • One kind of electroscope is made of two thin metal leaves attached to a metal rod with a knob at the top. • The leaves are allowed to hang freely • from the metal rod. Detecting Electric Charge