Lecture 3 Electric Charge and Coulomb's Law PDF

Electric Charge and Coulomb’s Law Dr/ Ahmed ElDrieny Lecture of physi c s general departm ent Fundamental Charge: The charge on one electron. e = 1.6 x 10 -19 C Unit of charge is a Coulomb (C) “ Two types of charge: Positive Charge: A shortage of electrons N...

Electric Charge and Coulomb’s Law Dr/ Ahmed ElDrieny Lecture of physi c s general departm ent Fundamental Charge: The charge on one electron. e = 1.6 x 10 -19 C Unit of charge is a Coulomb (C) “ Two types of charge: Positive Charge: A shortage of electrons Negative Charge: An excess of electrons Conservation of charge – The net charge of a closed system remains constant.  - Nucleus - - n + n - + + n n + n - + + n - - - Neutral Atom Number of electrons = Number of protons  - Nucleus - - n + n - + + n n + n - + + n - - - Positive Atom Number of electrons < Number of protons +2e = +3.2 x 10-19C  - Nucleus - - n + n - + + n n + n - + + n - - - Negative Atom Number of electrons > Number of protons -2e = -3.2 x 10-19C  Electric Forces Like Charges - Repel F F + + Unlike Charges - Attract F F - + Coulomb’s Law – Gives the electric force between two point charges. q1q2 F k 2 Inverse Square r Law k = Coulomb’s Constant = 9.0x109 Nm2/C2 q1 = charge on mass 1 q2 = charge on mass 2 r = the distance between the two charges The electric force is much stronger than the gravitational force. Two charges are separated by a distance r and have a force F on each other. q1q2 F k r2 F q2 F q1 r If r is doubled then F is : ¼ of F If q1 is doubled then F is : 2F If q1 and q2 are doubled and r is halved then F is : 16F Two 40 gram masses each with a charge of 3μC are placed 50cm apart. Compare the gravitational force between the two masses to the electric force between the two masses. (Ignore the force of the earth on the two masses) 3μC 3μC 40g 40g 50cm Two 40 gram masses each with a charge of 3μC are placed 50cm apart. Compare the gravitational force between the two masses to the electric force between the two masses. (Ignore the force of the earth on the two masses) 3μC 3μC 40g 40g 50cm Two 40 gram masses each with a charge of 3μC are placed 50cm apart. Compare the gravitational force between the two masses to the electric force between the two masses. (Ignore the force of the earth on the two masses) q1q2 FE  k 2 r 6 6 9 (3 10 )(3 10 )  9.0 10 2  0.324N (0.5) Two 40 gram masses each with a charge of 3μC are placed 50cm apart. Compare the gravitational force between the two masses to the electric force between the two masses. (Ignore the force of the earth on the two masses) m1m2 Fg  G 2 r (.04)(.04) 13  6.67 10 11 2  4.27 10 N (0.5) The electric force is much greater than the gravitational force Formative exam Good Bye