Two equally charges particles are 3 cm apart and repel each other with a force of 4 x10-5 N. Compute the charge on each particle.

Transcription

1 Physics QOD 12.3 Two equally charges particles are 3 cm apart and repel each other with a force of 4 x10-5 N. Compute the charge on each particle. q 1 = q 2 = 2 x 10-9 C

2 12.3 ELECTRIC FIELDS

3 Electric Fields The space around a concentration of electric charge is different from how it would be if the charge were not there. If you walk by the charged dome of an electrostatic machine a Van de Graaff generator, for example you can sense the charge. Hair on your body stands out just a tiny bit if you re more than a meter away, and more if you re closer. The space is said to contain a Electric Force field.

4 Electric Fields An electric field is a force field that surrounds an electric charge or group of charges.

5 Electric Fields A gravitational force holds a satellite in orbit about a planet, and an electrical force holds an electron in orbit about a proton. The force that one electric charge exerts on another is the interaction between one charge and the electric field of the other.

6 Electric Fields You can use electric field lines (also called lines of force) to represent an electric field. Where the lines are farther apart, the field is weaker. An electric field has both magnitude and direction. Since an electric field has both magnitude and direction, it is a vector quantity and can be represented by vectors.

7 Electric Field Lines The direction of an electric field at any point, by convention, is the direction of the electrical force on a small positive test charge. If the charge that sets up the field is positive, the field points away from that charge. If the charge that sets up the field is negative, the field points toward that charge. Magnitude of the field is indicated by the vector length. The electric field is greater where the vectors are longer.

8 Electric Field Lines You can use electric field lines to represent an electric field. Where the lines are farther apart, the field is weaker. For an isolated charge, the lines extend to infinity. For two or more opposite charges, the lines begin at a positive charge and terminate on a negative charge.

9 Electric Field Lines - Vectors a. In a vector representation of an electric field, the length of the vectors indicates the magnitude of the field. b. In a lines-of-force representation, the distance between field lines indicates magnitudes.

10 Electric Field Lines - Direction a. The field lines around a single positive charge extend to infinity. b. For a pair of equal but opposite charges, the field lines emanate from the positive charge and terminate on the negative charge. c. Field lines are evenly spaced between two oppositely charged plates.

11 Electric Field Lines Electrical Field Lines Single Point Charge

12 Electric Field Lines Electrical Field Lines positive and negative charge

13 Electric Field Lines The electric field inside a conductor is zero if it were not, the charges would move.

14 Electric Field Lines You can demonstrate electric field patterns by suspending fine thread in an oil bath with charged conductors. The photos show patterns for: a. equal and opposite charges; b.equal like charges; c. oppositely charged plates; d.oppositely charged cylinder and plate.

15 Electric Field Lines opposite charges

16 Electric Field Lines like charges

17 Electric Field Lines oppositely charged plates

18 Electric Field Lines oppositely charged cylinder and plate.

19 Electric Field Lines How are the magnitude and direction of an electric field determined? The length of the field lines and how far apart they are determine magnitude. The type of charge determines the direction of the field.

20 Electric Field Strength Electric Field Strength (E) is the amount of electrostatic force observed per charge. Formula: E = F/q E = Electric Field Strength (N/C) F = Electrostatic Force (Newton's) q = charge (Coulombs)

21 Electric Fields Assessment Questions Example #1 Two oppositely charged parallel metal plates, 1 cm apart, exert a force with a magnitude of 3.60 x N on an electron placed between the plates. Calculate the magnitude of the electric field strength between the plates.

22 Electric Fields Assessment Questions Example #2 What is the magnitude of the electric field intensity at a point where a proton experiences an electrostatic force of magnitude 2.3 x N?

23 Electric Fields Assessment Questions Example #3 The diagram represents an electron within an electric field between two parallel plates that are charged with a potential difference of 40 volts. If the magnitude of the electric force on the electron is 2 x N, find magnitude of the electric field strength between the charged plates.

24 Electric Fields Assessment Questions Example #4 Based on the diagram below, find: a. The magnitude of the electrostatic force between the spheres b. Direction of the electric field at point P (Right, Left, Up or Down?)

25 Electric Fields Assessment Questions Example #5 In the diagram below, P is a point near a negatively charged sphere. What direction best represents the direction of the electric field at point P? (Left, Right, Up or Down)

26 Electric Fields Assessment Questions Example #6 Sketch at least four electric field lines with arrowheads that represent the electric field around a negatively charged particle.

27 Electric Fields Assessment Questions Example #7 An electric field has: a. no direction. b. only magnitude. c. both magnitude and direction. d. a uniformed strength throughout.

28 Electric Fields Assessment Questions Example #8 In the electric field surrounding a group of charged particles, field strength is greater where field lines are: a. thickest. b. longest. c. farthest apart. d. closest.

29 Electric Fields Assessment Questions Example #9 A beam of electrons is produced at one end of a glass tube (as shown) and lights up a phosphor screen at the other end. If the beam passes through the electric field of a pair of oppositely charged plates, how is the beam deflected? (Up, down, into the page, out of the page)