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Electric Field Strength

Electric Field Strength. EFS (by definition). The electric field strength, E , is the force, F elec , per unit charge, q , at a point. The equation for EFS is (arrows show the units for each symbol) E = F elec q. N/C. N. C. Electric Field Strength.

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Electric Field Strength

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  1. Electric Field Strength

  2. EFS (by definition) • The electric field strength, E , is the force, Felec, per unit charge, q, at a point. The equation for EFS is (arrows show the units for each symbol) E = Felec q N/C N C

  3. Electric Field Strength • Steps to measure EFS, E, at some point. • Place small + test charge (q) at that point • Measure the force (Felec) exerted on the test charge • Divide force by the size (amt.) of test charge

  4. Example Problems • If the electric field strength due to some charged object is 1.5E3 N/C, find the force on a positive charge due to 2E-4 C placed in the field. • Known: E = 1.5E3 N/C & q = 2E-4 C • Unknown = Felec • Equation: E = Felec / q (solve for Felec)

  5. Example Problems (cont.) Felec = (1.5E3 N/C) x (2E-4 C) = 0.30 N • If the charge on the object in example #1 was doubled, does that change the electric field strength? Hint: what change would increasing q have on Felec?

  6. Example Problem (cont.) • Increasing q will increase Felec so ratio between the two is constant. • Conclusion = size of test charge doesn’t effect “E”

  7. EFS Lines of Flux • Directions & Strength of Electric Field (on board) • Facts: • More flux lines indicates a stronger electric field • Lines of flux should always be drawn so they are perp. to surface of the charge • Lines of flux should never cross

  8. Coulomb’s Law Review • Coulomb’s Law: the electric force is directly proportional to the product of their charges and inversely proportional to the square of the distance between their charges. Felec = K x q1x q2 d2

  9. Coulomb’s Law Review (cont.) • Facts: • Increasing the amount of charge will increase the electric force • Increasing the distance between the charges will decrease the electric force • Felec is + if the 2 charges are alike indicating that they will repel each other • Felec is – if the 2 charges are different indicating that they will attract each other

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