[PHY] Chapter 16 - Static Electricity

DARRELL ER (COPYRIGHTED) © TOPIC 16: STATIC ELECTRICITY DARRELL ER (COPYRIGHTED) ©

CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE DARRELL ER (COPYRIGHTED) ©

ELECTRIC CHARGE CHARGING INSULATORS CHARGING CONDUCTORS KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

HOW CHARGES BEHAVE LAW OF ELECTROSTATICS Unlike charges attract and like charges repel. DARRELL ER (COPYRIGHTED) © A neutral body has equal amount of positive and negative charge. Neutral metal ball Positively charged sphere Induced charges Electrons will flow into the metal sphere They are both positively charged now. They repel each other.

CHARGING INSULATORS RUBBING / FRICTION When rubbed with another material, electrons are transferred from one material to another. DARRELL ER (COPYRIGHTED) © LAW OF CONSERVATION OF CHARGE Take note that during this entire process, charges are only transferred from one object to another and charges are neither created nor destroyed.

CHARGING CONDUCTORS INDUCTION Using an external charged object to induce a charge in conductors. DARRELL ER (COPYRIGHTED) © INDUCTION 1) Put 2 neutral metal spheres side by side, in contact with one another. 2) Use a negative rod and place it near Sphere A, without actually touching it. 3) Since like charges repel and unlike charges attract, electrons in Sphere A will travel away to Sphere B. This will result in an uneven charge distribution as seen in the diagram where Sphere A has more positive charges while Sphere B has more negative charges. 4) While keeping the negative rod near Sphere A, separate both the spheres. When they are no longer in contact and electrons are not free to move within the spheres, remove the negative rod. Sphere A Sphere B Sphere A Sphere B

CHARGING CONDUCTORS INDUCTION + EARTHING Inducing charges on a single sphere, then earthing the sphere such that electrons are transferred to/from the ground and only the induced charges remain. DARRELL ER (COPYRIGHTED) © INDUCTION + EARTHING 1) Use a negative rod and place it near the sphere, without actually touching it. 2) Since like charges repel and unlike charges attract, electrons will be repelled and move the side B, leaving the positive charges in Side A. 3) The sphere is then earthed with a finger touching side B, with the negative rod still in place. Electrons will flow from the sphere to the ground and making side B neutral. 4) While keeping the negative rod at side A, remove the finger. The sphere is now left with a positive charge. A B A B e-

CHARGING CONDUCTORS CHARGE BY CONTACT A very direct way of charging by making a direct physical contact to facilitate the transfer of charges. DARRELL ER (COPYRIGHTED) © CHARGE BY CONTACT 1) A positively charged sphere comes in contact with the neutral metal ball. 2) Upon contact, the electrons will flow from the neutral metal ball to neutralise the positively charged metal sphere. 3) Separate both the objects. Both objects are now positively charged although the sphere now is less positively charged than before. Electrons will flow into the metal sphere They are both positively charged now. They repel each other.

DISCHARGING DISCHARGING INSULATORS 1) Expose to a flame, thermal energy from the flame ionises the air particles to produce negative and positive ions, which will discharge an object. 2) Expose to moisture, in moist conditions, water vapour in the air removes excess charges. DISCHARGING CONDUCTORS 1) Earthing, connect the object to the ground (earth) with a conducting wire or by touching it with a finger. DARRELL ER (COPYRIGHTED) ©

ELECTRIC FIELD BETWEEN POINT CHARGES ELECTROSTATIC HAZARD APPLICATION OF ELECTROSTATIC KEY CONCEPT DARRELL ER (COPYRIGHTED) ©