Ch20.1 – Static Electricity Like charges repel, opposites charges attract Protons can’t be touched (except in nuclear rxns) only electrons can be transferred between substances. Electricity is the flow of electrons. Static electricity is a short flow of electricity. Exs: a shock, the Van de graaf, a lighting bolt, static, etc. Neutral objects have an equal # of protons and electrons. (-) charge = excess electrons. (+) charge = lacking electrons Some objects gain electrons easier than others Protons

Triboelectric Sequence Rubber Plastic Copper Amber Wood Cotton Aluminum Human skin Silk Lead Cat fur Quartz Wool Glass Rabbit fur Asbestos Easier to lose electrons Easier to gain electrons When 2 materials are rubbed together, one gains electrons, becomes (–) charged. Other loses electrons, becomes (+) charged. Charge is always conserved. Ex: PVC plastic and rabbit fur: + =

Insulators and Conductors Insulators - have the ability to hold charge and confine it to a region for a longer period of time. Conductors - allow charge to flow freely until charge is equally spread out. Copper wire: All metals are good conductors.

Water is a good insulator (doesn’t allow charge to flow very well.) - add salt (puts ions in there), becomes an excellent conductor. Air is a better insulator. (down jackets) -must place enough charge near by, ions in air will align, charge will flow. Charge a conductor, charge seek making separation

Ch20 HW#1 1 – 5

1) a.) static electricity is a ______ of electricity. b.) When atoms become charge they gain/lose _____. c.) Two materials touch, electrons transfer. Overall, charge is____. d.) Materials that allow charge to flow freely are_____. e.) Materials that hold charge to region are____. f.) Distilled water is a good _____. g.) Adding salt to water makes it conduct because salt adds _____. h.) Air is a good ______. 2. PVC rubbed with wool. What charge does each get? 3. Glass & humans skin? 4. 2 charges of + 6.0C are separated by 0.50m. Find force.

Ch20 HW#1 1 – 5 1) a.) static electricity is a ______ of electricity. b.) When atoms become charge they gain/lose _____. c.) Two materials touch, electrons transfer. Overall, charge is____. d.) Materials that allow charge to flow freely are_____. e.) Materials that hold charge to region are____. f.) Distilled water is a good _____. g.) Adding salt to water makes it conduct because salt adds _____. h.) Air is a good ______. 2. PVC rubbed with wool. What charge does each get? 3. Glass & humans skin? 4. 2 charges of + 6.0C are separated by 0.50m. Find force.

Ch20 HW#1 1 – 5 1) a.) static electricity is a ______ of electricity. b.) When atoms become charge they gain/lose _____. c.) Two materials touch, electrons transfer. Overall, charge is____. d.) Materials that allow charge to flow freely are_____. e.) Materials that hold charge to region are____. f.) Distilled water is a good _____. g.) Adding salt to water makes it conduct because salt adds _____. h.) Air is a good ______. 2. PVC rubbed with wool. What charge does each get? 3. Glass & humans skin? 4. 2 charges of + 6.0C are separated by 0.50m. Find force. (repels)

5. A + 2C & + 3C charge are separated by 4.5 m. Force?

(repel)

Electroscopes – Charge Detectors

Electroscopes – Charge Detectors

+ + + Electroscopes – Charge Detectors

Electroscopes – Charge Detectors Don’t indicate if the charge is + or –. Leaves always spread when either charge is present

Electroscopes – Charge Detectors Induction – a neutral object feels the presence of a charge - caused by the electric field. (Ch 16) As the charged object is brought near the neutral object, it induces a charge in the neutral object

Ex1) Two charges are separated by 3.0 cm. Object A has a charge of +6.0μC, while object B has a charge of +3.0μC. What is the force on object A?

Ex2) A sphere with a charge of +6.0μC is located near 2 other charge spheres. A -3.0μC sphere is located 4.00 cm to the right and a +1.5μC sphere is located 3.00 cm directly underneath. Determine the net force on the 6.0μC sphere. Ch20 HW#2 6 – 10

Lab20.1 Statics - due tomorrow - Ch20 HW#2 due at beginning of period

Ch20 HW#2 6 – A -2x10 -4 C charge and a +8x10 -4 C charge separated by 0.30m. Find force. 7. A -3mC charge and a -6.2mC charge are placed 1.5m apart. Find force. 8. A +10μC charge & -10μC charge 1m apart. Force?

Ch20 HW#2 6 – A -2x10 -4 C charge and a +8x10 -4 C charge separated by 0.30m. Find force. (attract) 7. A -3mC charge and a -6.2mC charge are placed 1.5m apart. Find force. (repel) 8. A +10μC charge & -10μC charge 1m apart. Force? (attract)

9. A -6X10 -6 C charge exerts and attractive force of 65N of a 2 nd charge.05m away. Find 2 nd charge. 10) A +1C charge & +2C charge at 1.0m,2.0m,3.0m,4.0m,5.0m. Find force.

9. A -6X10 -6 C charge exerts and attractive force of 65N of a 2 nd charge.05m away. Find 2 nd charge. 10) A +1C charge & +2C charge at 1.0m,2.0m,3.0m,4.0m,5.0m. Find force.

9. A -6X10 -6 C charge exerts and attractive force of 65N of a 2 nd charge.05m away. Find 2 nd charge. 10) A +1C charge & +2C charge at 1.0m,2.0m,3.0m,4.0m,5.0m. Find force.

Ch21.1 – Electric Fields E-fields - test with a small (+) test charge (+q o ) – – – – – – – – ––

  Units: Ex1) A +1μC test charge experiences a force of.01N to the right, as show. What is the magnitude of the E-field? Label the charge as (+) or (-)F E Ex2) A +2nC test charge experiences a force of 2.5mN to the left. What is the mag of the E-field. Label the E-field creater as (+) or (-). F E + +

Ex3) What is the strength of an E-field created by a +3.0 mC charge, at a distance of 85cm? Ch21 HW#1 1 – 7

1. A +2.0x10 -8 C test charge experiences a force to the right of 0.060N by an E-field. Find it, label charge. F E 2. A +4μC test charge experiences a force of 0.10 N to the left in an E-field. Find it and label it. F E 3. A 5.5μC test charge experiences a force of 2mN to the left in an E-field. Find it and label it. + +

Ch21 HW#1 1 – 7 1. A +2.0x10 -8 C test charge experiences a force to the right of 0.060N by an E-field. Find it, label charge. F E 2. A +4μC test charge experiences a force of 0.10 N to the left in an E-field. Find it and label it. F E 3. A 5.5μC test charge experiences a force of 2mN to the left in an E-field. Find it and label it. F E + + – + + –

4. A positive test charge of 5x10 -4 C is in an E-field that exerts a force of 2.5x10 -4 N on it. Find the E-field at that location. 5. You probe the field of an unknown charge. 1 st with a 1μC test charge then with a 2μC. a.)Do they experience the same force? b.)Same field? c.) If E-field is 1x10 -5 N/C, what is the force on each?

4. A positive test charge of 5x10 -4 C is in an E-field that exerts a force of 2.5x10 -4 N on it. Find the E-field at that location. 5. You probe the field of an unknown charge. 1 st with a 1μC test charge then with a 2μC. a.)Do they experience the same force? b.)Same field? c.) If E-field is 1x10 -5 N/C, what is the force on each? a.b. c.

6. What is E-field at a distance of.25m from +1μC charge? 7. An E-field of 6X10 -7 N/C at a distance of 2.5m. What charge creates it?

6. What is E-field at a distance of.25m from +1μC charge? 7. An E-field of 6X10 -7 N/C at a distance of 2.5m. What charge creates it?

6. What is E-field at a distance of.25m from +1μC charge? 7. An E-field of 6X10 -7 N/C at a distance of 2.5m. What charge creates it?

Ch21.2 – Electric Potential Where is PE G greatest? Greatest PE E Earth

Ch21.2 – Electric Potential Where is PE G greatest? High PE E Low PE E Greatest PE E Low PE E High PE E High PE E Low PE E Potential Difference: Units: Earth

Equipotentials - areas where the potential doesn’t change. ΔV = E. d Ex1) 2 parallel plates are charged up. A voltmeter measures the potential diff to be 60.0V. The plates are 3.0cm apart. What is the magnitude of the E-field between them? – – – – – – – –

Ex2) 2 large, charged parallel plates are 4.0 cm apart. If the E-field measures between the is 625N/C: a) What is the electric potential? b) How much work is done moving a proton (+1.6X C) from the (-) plate to the (+) plate? Ch21 HW#2 6 – 9

6. What is the change in potential when an external force does 10J of work to move a +1μC charge? 7. How much work is done by the E-field to move a +10mC charge to a location where the potential is 10V lower? 8. A charged PVC pipe creates an E-field of roughly 1x10 3 N/C at a distance of 0.05m from it. What is the potential?

Ch21 HW#2 6 – 9 6. What is the change in potential when an external force does 10J of work to move a +1μC charge? 7. How much work is done by the E-field to move a +10mC charge to a location where the potential is 10V lower? 8. A charged PVC pipe creates an E-field of roughly 1x10 3 N/C at a distance of 0.05m from it. What is the potential?

8. A charged PVC pipe creates an E-field of roughly 1x10 3 N/C at a distance of 0.05m from it. What is the potential? 9. 2 charged parallel plates have a potential diff of 12.0V when separated by 1.0cm. E-field?

8. A charged PVC pipe creates an E-field of roughly 1x10 3 N/C at a distance of 0.05m from it. What is the potential? 9. 2 charged parallel plates have a potential diff of 12.0V when separated by 1.0cm. E-field?

Ch21.3 – Capacitance - the ability to store charge All objects can store some amount of charge. Q = V. C Units: charge potential capacitance stored diff Most capacitors are made of 2 metal sheets, separated by an insulator, and rolled up into a cylinder. Ex1) In your next lab, you will use a 22,000μF cap that is connected to a 6V battery. How much charge should it store?

Ex2) A sphere has an electric potential difference between it and the earth of 60V, when it is charged to 3μC. What is its capacitance? Circuit symbols: Battery Capacitor Resistor Switch Light Emitting Diode (LED) or Make these circuits: RR R 6V 6V 40,000μF 40,000μF Ch21 HW#3 10 – 14

Lab21.1 – Capacitance - due tomorrow - Ch21 HW#3 due at beginning of period

Ch21 HW#3 10 – A 27μF capacitor has an electric potential difference of 25V across it. What is its charge? 11. A 6.8μF capacitor is connected to a 15V battery. What is its charge? 12. A 3.3μF cap is charged to 2.5x10 -7 C. What is its potential?

Ch21 HW#3 10 – A 27μF capacitor has an electric potential difference of 25V across it. What is its charge? Q = V. C = (25J/C)(27x10 -6 C) = 11. A 6.8μF capacitor is connected to a 15V battery. What is its charge? Q = V. C = (15V)(6.8x10 -6 C) = 12. A 3.3μF cap is charged to 2.5x10 -7 C. What is its potential?

13. A 1.5C test charge is moved by an external force that does 25J of work to move the test charge to a higher potential. What is the change in potential? 14. A +2.5C test charge is moved by an E-field that does 10J of work to move the test charge to a lower potential. What is the change in potential?

13. A 1.5C test charge is moved by an external force that does 25J of work to move the test charge to a higher potential. What is the change in potential? 14. A +2.5C test charge is moved by an E-field that does 10J of work to move the test charge to a lower potential. What is the change in potential?

Ch20,21 Review 1. 2 charges q A and q B are separated by a distance d and exert a force F on each other. How does the force change if: a. q A and q B are doubled? b. d is cut in half? c. q A is doubled and d is doubled? 2. Find net force:

A = 2C B = 4C m | 2m | C = 3C ++ +

3. A positive test charge of 1.0x10 -5 C experiences a force of 0.20N when located at a certain point. Find the E-field.

4. Sketch the fields: a)b) c) +1μC -2μC +–

5. If 120J of work are performed to move a +5.5C chrage from a (-) plate to a (+) plate. Find the ΔV. + or – work? 6. A voltmeter indicates that the electric potential difference between 2 plates is 50.0V. Plates are 0.020m apart. Find E-field. 7. What is the charge stored in a 15.0pF capacitor when it is connected to a 75V source? – – – – – – – – – – – – – – – –

8. 2 pith balls with masses of 1.0g and charges of 2.4x10 -8 C, as shown. Find force cm--- ++