1. Ying Yi PhD HCC Lab 2: Electric Field Lines 1

2. Electricity phenomena 2

3. Charge Definition : When a glass rod rubbed with fur, the excess electric charge is called positive charge; when a plastic rod rubbed with silk, the excess electric charge is called negative charge. Property : Like charges repel one another and unlike charges attract one another. Conservation Law : Electric charge is always conserved. 3

4. Electric force Coulomb constant 8.9875×10 9 N∙m 2 /C 2 Distance between two charges Charge 1Charge 2 4 Electric Force

5. Electric Field 5 The electric field can be written as The direction of the electric field at a point in space is defined to be the direction of the electric force that would be exerted on a small positive charge placed at that point. The magnitude is Michael Faraday

6. Electric field lines 6 Michael Faraday 1. The electric field E is tangent to the electric field lines at each point. 2. The number of lines per unit area through a surface perpendicular to the lines is proportional to the strength of the electric field in a given region. The relation between electric field and electric field lines

7. Electric Field lines for single charges 7 (Positive charge electric field)(Negative charge electric field) The field lines are originated from the positive charge. The field lines end up at the negative charge. Electric field lines for multiple charges will be?

8. The rules for drawing electric field lines 8 1.Begin on positive charges and end on negative charges. In the case of an excess of charge, some lines will begin or end infinitely far away. 2.The number of lines drawn leaving a positive charge or ending on a negative charge is proportional to the magnitude of the charge. 3.No two field lines can cross each other.

9. Electric field lines for electric dipole 9

10. Equipotential lines 10

11. To do list 11 Draw the equipotential lines surrounding two point charges, graph and examine the Electric Field lines produced by the point charge. Draw the equipotential lines surrounding parallel conducting plates like those in a capacitor, graph and examine the electric field lines produced by the plates. Draw the equipotential lines surrounding circular configuration, graph and examine the Electric Field lines produced by the configuration.

12. Procedures 12 1. Place two small spots of conducting ink on the carbon paper with distance about 20 cm 2. Place metal pins on these spot, make sure the pins are firmly contact the carbon paper. 3. Set the output of Power Supply to 10 volts. Connect the (+) end of power Supply to one pin and (-) to another. 4. Use the voltmeter to search the equipotential lines in the space between the two pins, select 2.0v, 4.0v, 6.0v, and 8.0v as the potential difference. Search 10 points along each voltage 5. Connect the 4 equipotential lines and smooth them out 6. Label each equipotential line 7. Draw the electric field lines between the two pins, they should be perpendicular to the equipotential lines. 8. Repeat 1 to 7 for parallel plates and circular configuration.

13. Questions 13 Field lines start on positive charges and end on negative charges. (True or False) When drawing field lines, the lines should always cross. (True or False) Electric field lines are used to describe the electric field around a charged object. (True or False) When two equally charged plates are placed over one another the field lines between them are completely straight and not evenly spaced. (True or False) In electrostatic representations electric field lines start on ________ charges and end on _______ charges. In the diagram below which particle has a negative charge and which one has a positive charge? (Left or right)