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Electrostatics

Part 3. Electrostatics. Electric Field vs Gravitational Field. The electric field can push AND pull charges Because there are two types of charges (+ and -) The gravitational field can only pull Only positive masses. Cause of Electric Field. Charges cause an electrical field.

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Electrostatics

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  1. Part 3 Electrostatics

  2. Electric Field vs Gravitational Field • The electric field can push AND pull charges • Because there are two types of charges (+ and -) • The gravitational field can only pull • Only positive masses

  3. Cause of Electric Field • Charges cause an electrical field. • Each charge creates its own electric field in the surrounding space. • Electric Field is a vector quantity • Has magnitude and direction • Use Electric Field lines(lines of force) to show the Electric Field

  4. Drawing the Electric Field • Electric field direction from charge that creates the field: • Away from positive charge • Toward negative charges • The lines begin on positive charges and end on negative charges. • Draw lines perpendicular to charge • Lines never cross

  5. Calculating the Electric Field • Electric field strength: • The closer to the charge, the stronger the field • The closer the field lines, the stronger the field • The farther away, the weaker the field

  6. Calculating the Electric Field • Electric field strength: • The number of lines are proportional to strength • The more lines the stronger the field

  7. Calculating the Electric Field • Electric field strength: (quantitative) E = kq/d2 • Depends on Charge and distance • E = Electric field strength (Newton/Coulomb, N/C) • k = 9.0 x 109 Nm2/C • q= charge causing the field (Coulomb, C) • d or r = distance (meters, m)

  8. Practice Problem 1 • A fly accumulates 3.0 x 10-10 C of positive charge as it flies through the air. What is the magnitude and direction of the electric field at a location 2.0 cm away from the fly? q = 3.0 x 10-10C d or r = 2.0 cm = _____ m E = ? equation E = kq/ r2 E = (9.0 x 109)(3.0x10-10) (0.020)2 E = 6750 N/C 0.020

  9. Charges in Electric Field Electric Field = force exerted on positive charge If +q = force in same direction (pull) of the field If -q = force in opposite direction (push) of the field

  10. The electric field… • The strength of the electric field… E = F/q • E = strength of the field (Newton/Coulomb, N/C) • F = Force exerted on charge in field (Newton, N) • q = charge (Coulomb, C) that sits in the field; experiences the force

  11. Practice Problem 2 A charge of -2.0 x10-6C is placed in a uniform electric field of strength 5000 N/C that points downward. What is the magnitude and direction of the force experienced by this charge?

  12. Practice Problem 2 A charge of -2.0 x10-6C is placed in a uniform electric field of strength 5000 N/C that points downward. What is the magnitude and direction of the force experienced by this charge? E = F / q 5000 N/C= F / (-2.0 x 10-6C) (-2x10-6 )(5000)=F -0.01N=F magnitude of the force direction? - 2 charge, the force on the electron is opposite the field!

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