Electrostatic Review

Strength of field? Map the field strength as a function of distance from charge. What does the slope tell you? What does the exponent tell you?

Potential? Map the potential as a function of distance from charge. What does the slope tell you? What does the exponent tell you?

Example 1 The objects at right have the same magnitude of charge. If the electric field in the center of charged objects is zero, which of the following is a possible combination of the sign on the charges? W X W X Y Z A + - B C D Y Z

Example 2 The objects at right have the same magnitude of charge. If the electric potential in the center of charged objects is zero, which of the following is a possible combination of the sign on the charges? W X W X Y Z A + - B C D Y Z

Why does the electric field get stronger closer to the negative charge? Why does the electric potential become more negative? What would you expect the electric field and potential to be between two positive charges?

Example 3 B A E x E x Suppose an object with a charge +5Q is fixed in place. An object with charge of +3Q sits at x distance away. Which of the following most closely represents the strength of the electric field? (assume a field pointing right is positive) C D E x E x

Field lines Interpret and use conventions for field lines to predict behavior of charged objects

Example 4 A B The object on the left has a charge of +2Q. The object on the right has a charge of -3Q. Which of the diagrams at the right correctly diagrams the field lines? C D

Behavior of charged objects in electric fields Predict how charged objects will behave in an electric field Potential energy is converted to kinetic energy ( 𝑃𝐸+𝐾𝐸) 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 = (𝑃𝐸+𝐾𝐸) 𝑓𝑖𝑛𝑎𝑙 𝑞𝐸 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 +0= 𝑞𝐸 𝑓𝑖𝑛𝑎𝑙 + 1 2 𝑚𝑣2

Example 5 A proton is released in a constant electric field. Which of the following snapshots shows the location of the proton at several different points in time? A B C D Vinit = 100 V Vfinal = 0 V

Equipotential Interpret and use conventions for equipotential lines to predict behavior of charged objects Compare isolines for gravitational potential and electrical potential energy

Example 6 In the diagram at right, A is a proton while B, C, and D are electrons. All are held in place initially. Which has the greatest potential energy? Which will end up with most kinetic energy when the particles are released? + V -V A B C D

Answers Example Answer 1 B, D 2 A, B 3 D 4 5 B 6 A