Ch9 - coulomb's law
- 1. • Charles Coulomb (1736-1806: French) – Studied relationship between force and charge Coulomb’s Law Unit of charge = 1 coulomb (C) The charge on 1 electron is (1.6 x 10-19 C)
- 2. • The LAW! – Force directly related to magnitude of the charges – Force inversely related to the square of the distance between the two charges Coulomb’s Law Fα q Q Fα 1 kq Q F= 2 r2 r F α qQ r2 k is a constant that corrects the proportion into an equality.
- 3. • This is similar to a formula • we talked about in Lesson 5. kQ q F = 2 Attractive Coulomb’s r Law or Newton’s Repulsive Law Of Only Universal GMAttractive m Gravitation F= r2
- 4. • Keep comparing: kQ q Coulomb’s Law F= 2 Product r of charges GMm F= r 2 Product of masses
- 5. • Keep Comparing: kQ q Coulomb’s Law F= 2 r Both are inverse- square GMm laws F= r2
- 6. • Keep Comparing Large kQ q Magnitude F= 2 r 9 x 109 N·m2/C2 Small GMm Magnitude F= r2 6.67 x 10-11 N·m2/kg2
- 7. Exponent Keys on Calculators: Borrow one from your instructor. Ipods and cell telephones don’t work well with exponent keys. TI 30: 2nd EE TI 83: 2nd EE Others: Might see exp, or x 10x These keys are used when decimal places are too many for the calculator to display or use. A number like .0000000000000000000000000003 so it needs to be typed by using the exponent key. TI 30: 3EE-28, others: 3exp-28
- 9. • Sample problem 1! YEAH! – What is the magnitude of the electrostatic force between 2 protons in the nucleus? (assume the distance to be 3.0x10-13 cm) Coulomb’s Law F= kq Q (9 (1.6 E10- (1.6 E 10- r2 = E109) 19 ) 19 ) (3.0 E 10 -15 ) 2 F =25.6 N
- 10. • Sample problem 2! – What is the magnitude of the gravitational force between 2 protons in the nucleus? (assume the distance to be 3.0x10 -13 cm) Coulomb’s Law GM m (6.67 x 10-11(1.67 x 10-27 (1.67 x 10- ) F= 2 = ) 27 ) r (3.0 x 10-15 )2 F = 2.07x10-35 N
- 11. Electric Fields: An area around a charged object that affects all other charged objects Unit: N/C The more the lines the stronger the field
- 12. Two More Rules for Drawing Electric Field Lines: Lines are always drawn out of the positive and into the negative. The more the lines the stronger the field.
Editor's Notes
- #2: 1 coulomb = The amount of electricity transported by a current of one ampere flowing for one second. About as many electrons that pass through 100-W bulb every second
- #3: What do we need to replace the ‘ α ’ with?
- #4: Electrostatic interactions may be attractive or repulsive, but gravity is ONLY attractive
- #6: The strengths of both gravity and electrostatic interactions decreases exponentially with distance
- #7: Gravity is MUCH weaker! Force due to electrostatic interactions is 2.27 x 10 39 times larger than the forces due to gravity
- #10: Because both protons have the same charge we replace q 1 q 2 with q 2 .