1. CHAPTER-21 Electric Charges

2. CHAPTER-21 Electric Charges Topics to be covered:  Types of electric charge  Forces among two charges (Coulomb’s law)  Charge quantization  Charge conservation

3. Ch 21-2 Electric Charges  Electric Charges: Intrinsic property of fundamental particles  Fundamental particles: electron, proton and neutron with negative, positive and zero charges respectively.  Objects : electrically neutral (containing positive and negative charges in equal number)  Electron charge = 1.602x 10 -19 Coulomb (C)  Charged Object : Objects having net excessive charge of specific type  Negatively or positively Charged Objects: objects containing excessive electrons or missing electrons respectively.

4. Ch 21-2 Electric Charges  Charging an object: Placing a charge on an object  Charging a glass rod in rubbing with silk: glass rod losses electrons- glass rod positively charged  Charging a plastic rod in rubbing with fur : plastic rod gain electrons- plastic rod negatively charged silk glass rod silk glass rod - - - - + + + +

5.  Glass rod repels glass rod.  Similar charges repels each other  Plastic rod attracts glass rod.  Opposite charges attracts each other Ch 21-2 Electric Charges

6.  Conductors: Materials through which charges can move freely  Insulators (Non-Conductors): Materials through which charges cannot move  Semiconductors: Materials having properties between conductors and insulators  Superconductors: Perfect conductors allowing charges to move without any hindrance. Ch 21-3 Conductors and Insulators

7.  Coulomb Law: The electrostatic force of attraction or repulsion F between two charges is:  F= k  q 1  q 2  /r 2  Direction of F:  similar charges (Repulsion): away from each other.  opposite charges (Attraction): towards each other Ch 21-4 Coulomb Law

8.  Zero Force Position between three charges along a line:  Pair of opposite charges: on the side of the charges, closer to weaker charge  Pair of similar charges: between the charges and closer to weaker charge

9. Ch 21-5, 6 Charge Quantization and Charge Conservation  Charge Quantization: Charge on objects is integer multiple of elementary charge e=1.602x 10 -19 C  charge q= ne where n is a positive or negative integer number.  Charge Conservation: Net electric charge of an isolated system is conserved and cannot change

10. Ch 21- 6 Charge Conservation Conservation of Charge  If we rub the uncharged glass rod with the silk cloth, as shown in the upper figure  positive charge appears on the rod (see lower figure).  equal amount of negative charge appears on the silk cloth  net rod-cloth charge is zero.. silk glass rod silk glass rod - - - - + + + +