1. Current and Resistance Electric Charge and Coulomb`s law Lecture 20 Monday: 29 March 2004

2. Charge (q) q is measured in coulombs (C) q can be + or – q is conserved q is quantized The elementary charge is: e = 1.6 ×10 -19 C

4. Forces on Charges Unlike charges attract. Like charges repel.

5. Coulomb’s Law

6. Central Force (acts along the line connecting the two objects) “one over r squared force” Is mathematically identical to gravitational force. But they are not the same force.

7. ELECTROSTATIC VS. GRAVITATIONAL FORCE Electron: m e = 9.11 × 10 -31 kg q e = – e = – 1.6 × 10 -19 C Proton: m p = 1.67 × 10 -27 kg q p = e = 1.6 × 10 -19 C

8. ELECTROSTATIC VS. GRAVITATIONAL FORCE A proton and an electron are attracted to each other by two forces:

9. ELECTROSTATIC VS. GRAVITATIONAL FORCE

10. Comparison of Gravity and Electrostatic Force