AP L3 Charge and its types explaination.pptx

science

1. Contents Name the unit of charge Type of charge Attractive and repulsive forces Amount of charge on a given number of electron Point Charges of different magnitudes Equal but opposite field charges Unequal and opposite field charges 1

2. Electrical charge The charge of an electron and that a proton are equal in magnitude. Electrical property of matter: Excess of electrons Deficiency of electrons Symbolized by Q 2

3. Unit of charge 3

4. Types of Charge Positive and negative charge: 4 There is a force ( F ) between charges. Like charges repel; unlike charges attract. The force is directly proportional to charge. The force is inversely proportional to square of distance.

5. Single Positive Field Charge + Keep in mind that the field lines radiate outwards because, by definition, an electric field vector points in the direction of the force on a positive test charge. The nearer you get to the charge, the more uniform and stronger the field. Farther away the field strength gets weaker, as indicated by the field lines becoming more spread out.

6. Single Negative Field Charge - The field surrounding an isolated, negative point (or spherically symmetric) charge looks just like that of an isolated positive charge except the field lines are directed toward the field charge. This is because, by definition, an electric field vector points in the direction of the force on a positive test charge, which, in this case is toward the field charge. As before, the field is stronger where the field lines are closer together, and the force vector on a test charge is parallel to the field.

7. Point Charges of Different Magnitudes + 1 Let’s compare the fields on two separate isolated point charges, one with a charge of +1 unit, the other with a charge of +2 units. It doesn’t matter how many field lines we draw emanating from the +1 charge so long as we draw twice as many line coming from the +2 charge. This means, at a given distance, the strength of the E field for the +2 charge is twice that for the +1 charge. + 2

8. Equal but Opposite Field Charges Pictured is the electric field produced by two equal but opposite charges. Because the charges are of the same magnitude, the field is symmetric. Note that all the lines that emanate from the positive charge land on the negative charge. Also pictured is a small positive charge placed in the field and the force vector on it at that position. This is the vector sum of the forces exerted on the test charge by each field charge. Note that the net force vector is tangent to the field line. This is always the case. In fact, the field is defined by the direction of net force vectors on test charges at various places. The net force on a negative test charge is tangent to the field as well, but it points in the opposite direction of the field. (Continued on next slide.) + - Link #1 Link #2 Link #3

9. + + More field lines emanate from the greater charge; none of the field lines cross and they all go to infinity. The field lines of the greater charge looks more like that of an isolated charge, since it dominates the smaller charge. If you “zoomed out” on this picture, i.e., if you looked at the field from a great distance, it would look like that of an isolated point charge due to one combined charge. Two + Field Charges of Different Magnitude Although in this figure the greater charge is depicted as physically bigger, this need not be the case.

10. Opposite Signs, Unequal Charges + - The positive charge has a greater magnitude than the negative charge. Explain why the field is as shown. (Answer on next slide.)

11. Opposite Signs, Unequal Charges (cont.) More field lines come from the positive charge than land on the negative. Those that don’t land on the negative charge go to infinity. As always, net force on a test charge is the vector sum of the two forces and it’s tangent to the field. Since the positive charge has greater magnitude, it dominates the negative charge, forcing the “turning points” of the point to be closer to the negative charge. If you were to “zoom out” (observe the field from a distance) it would look like that of an isolated, positive point with a charge equal to the net charge of the system. + -

12. Summary of Fields due to Unequal Charges You should be able to explain each case in some detail.

13. Coulomb’s Law A force (F) exists between two charges (Q1, Q2) that is directly proportional to product of the two charges and inversely proportional to the square of the distance (d) between the charges. Where K is constant of proportionality 13

14. Coulomb’s law constant Coulomb experimentally observed that force between two point charges placed 1 meter apart is 14

15. The End