1. Daily Warm-Up How is the size of the force acting on two charges related to the distance between the charges? How is the size of the charges related to the size of the force? A proton and an electron are held in place on the x- axis. The proton is at x = +d, the electron is at x= -d. They are relaeased simultaneously and the only forces to affect their motions is the electrostatic force of attraction that each applies to the other. Which particle reaches the origin first?

2. What is a Coulomb? A Coulomb is a unit used to measure the amount of charge. One electron has a charge of -1.6x10 -19 C How many electrons are contained in the following charges:  -6.4x10-19 C  -4.8mC  3.2x10-19 C  1C of negative charge

3. Electric Field Strength F = Eq where: F = Force in N E = Strength of electric field in N/C q = Charge in C What is the equation for calculating the strength of an electric field?

4. Sample Question Electric Field Strength A small charge, 2x10 -9 C, experiences a force of 1.5x10 -4 N in an electric field. What is the strength of the electric field? A charge of 6x10 -6 C is placed in the same field. What is the force on the charge?

5. Daily Warm-Up Change the following numbers into the indicated units:  7.5x10 4 m in km  0.034mC in Exp  24ns in Exp  1 week in seconds  3.5x10 -5 C in  C Convert 120 yards to km. 8km = 5mi 3ft = 1 yard 5280ft = 1 mile Convert 42 miles to cm 12 in = 1 ft 2.54 cm = 1 in

6. Practice Problems 1)A positive charge of 5 x10 –4 C is in another charge’s electric field. It experiences a force of 2.5 x10 –4 N to the left. What is the magnitude and direction of the electric field at that point? 2)If you replaced the previous positive charge with one that is twice as large and placed it in the same spot in the same electric field a. Would the new charge have the same size force acting on it? Why? b. Would you find the same size electric field? Why?

7. Practice Problems 3)A negative charge of 2.0 x10 –8 C experiences a force of 0.06N to the right in another charge’s electric field. a. What is the field magnitude and direction at that point? b. Can you positively tell if it’s a positive or a negative charge creating the field? Why? 4)A tiny ball (mass = 0.024 kg) carries a charge of – 21  C. What electric field (magnitude and direction) is needed to cause the ball to float above the ground?

8. Answers 1).5 N/C left 2a) No 2b) Yes 3a) 3 E6 left 3b) No 4) 11000 N/C