# Electric Field Physics Mrs Coyle Analogy The electric

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Electric Field Physics Mrs. Coyle

Analogy The electric field is the space around an electrical charge just like a gravitational field is the space around a mass.

Electric Field n Space around a charge.

What is the difference?

Van de Graaff Generator n Builds up static electric charges.

Electric Field Vector, E n E = F/ qo n qo , positive test charge n E is a vector quantity n Unit: N/C n E is analogous to the gravitational field, g, where g=F/m

Example 1 n A charge of 3µC is used to test the electric field of a central charge of 6 C that causes a force of 800 N. What is the magnitude of the electric field? n Answer: 2. 7 x 108 N/C

Electric Field http: //higheredbcs. wiley. com/legacy/colleg e/halliday/0471320005/simulations 6 e/inde x. htm? newwindow=true

Electric Field Lines

Electric Field Lines of two Positive Charges

Electric Field Lines n Lines that indicate the strength and direction of the electric field. n The more dense the lines, the stronger the field. n Electric field vectors are tangent to the curve. n Simulation http: //online. cctt. org/physicslab/content/applets/ pointcharges/elefi_z. htm

Conductors and Electric Fields (under electrostatic conditions) n “The electric field is zero inside a charged conductor”. n “Excess charge on an isolated conductor resides on the surface”. n “Excess charge accumulates on sharp points”. n Electric field lines meet the conductor perpendicular to the surface of the conductor.

Shielding n The electric field is zero inside a charged conductor.

Where are you safe during a thunderstorm? A) In a car B) Outdoors or

Why can you not get radio reception in a tunnel or in a steel bridge?

Which field is stronger? n. A B

Electric Field for a Point Charge Using E=F/qo and Coulomb’s Law prove: E=k Q ______ r 2 where Q is the central charge.

Example 2 n A test charge of +3µC is located 5 m to the east of a -4µC charge. n A) Find the electric force felt by the test charge. n B) Find the electric field at that location. n Answer: 4. 32 x 10 -3 N, 1. 44 x 103 N/C along the –x axis.

Example 3 n If a test charge is moved to a location three times as far as its original location, how does the electric field change?

Example 4 n Calculate the electric field felt by a test charge located half way between a charge of +1 C and a charge of -3 C, that are 2 m apart. n Answer: 1. 8 x 1010 N/C