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Electrostatics and the Electric Field

Electrostatics and the Electric Field. 1. When the balloon is rubbed on the sweater, what might happen?. 1 . When the balloon is rubbed on the sweater, what might happen?. A. Some positive charges in the sweater will move onto the balloon

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Electrostatics and the Electric Field

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  1. Electrostatics and the Electric Field

  2. 1. When the balloon is rubbed on the sweater, what might happen?

  3. 1. When the balloon is rubbed on the sweater, what might happen? A. Some positive charges in the sweater will move onto the balloon B. Some negative charges in the sweater will move onto the balloon

  4. 2. What do you think will happen when the balloon is moved closer to the wall? Neutral wall Negatively charged balloon

  5. 2. What do you think will happen when the balloon is moved closer to the wall? • Some positive charges in the wall will move towards the balloon • Some negative charges in the wall will move towards the balloon • Some positive charges in the wall will go onto the balloon • Some negative charges on the balloon will go to the wall

  6. 3. What do you think the balloons will do? Negatively charged balloon Negatively charged balloon

  7. 3. What do you think the balloons will do? • The balloons will move towards each other B. The balloons will move away from each other C. The balloons will not move.

  8. 4. What might happen to the charge on the man when he touches the door knob?

  9. 4. What might happen to the charge on the man when he touches the door knob? • Most electrons will go into the knob and down to the earth. B. Some electrons will go from the earth through the knob and into the man.

  10. Electric Force • Charges create a force • The force causes objects to either repel or attract • Electric force is a non-contact force . . . it causes action between charges without the charges coming in contact • Non-contact forces are often called “field” forces (like the gravitational force)

  11. Electric Field • We can call the space around a charged object the electric field • The electric field exerts a force on objects within the field • The size of the force is based on the amount of charge present and the distance between objects

  12. Electric Field • The electric field is a vector quantity • It has a magnitude and a direction • The direction of the field can be measured using a positive test charge (as a standard) • http://phet.colorado.edu/sims/charges-and-fields/charges-and-fields_en.html

  13. Electric Field Lines • To show direction, electric field lines are drawn around the charges within an electric field • The electric field is stronger where the field lines are closer together • Arrows move away from a positive charge (because a positive charge repels the positive test charge)

  14. Electric Field Lines • Electric field lines point toward a negative charge (because a negative charge attracts the positive test charge) • Electric field lines are also called lines of force

  15. Electric Field Direction

  16. Electric Field Magnitude

  17. Note: If you substitute “F” from the Coulomb’s law equation into the “F” of the electric field equation, you get the following:

  18. Example 1 There is an electric field in the atmosphere surrounding the Earth which has a magnitude of roughly 150 N/C and a direction pointing towards the center of the Earth. Determine the magnitude and the direction of the force experienced by a dust particle having a negative charge of 9.2x10-16 C.

  19. Potential Energy • Review . . . Potential energy is due to an objects position • All energy is measured in joules • For an object to gain gravitational potential energy, work must be done on the object • Example: a book is lifted into the air and gains gravitational potential energy

  20. Electric Potential Energy • The energy gained by an electric charge when work is done on the charge is called electric potential energy • Work is done on the charge when it is moved against an electric field • Example: A negatively charged balloon is pushed toward a Van de Graff generator • Once the charge is released, the electric potential energy becomes kinetic energy

  21. Electric Potential • Electric potential is a comparison of the electric potential energy and the number of charges present • A balloon charged by rubbing it on your hair does not have many charges (only about 1 millionth of a Coulomb) • This is why a balloon doesn’t shock you . . .it can have high voltage, but not enough charge to harm you

  22. Electric Potential

  23. Example 2 How much energy is stored when 7.2 C of charge is moved through a potential difference of 1.5 V?

  24. Review • What is the space surrounding a charged particle called? • How does a charged particle gain electric potential energy? • Is the strength of an electric field effected by distance? If so, how? • What is a volt? Electric field Work must be done on the charge. The field strength increases as the distance decreases. 1 Joule/1 Coulomb (unit for electrical potential)

  25. Tesla Coil • A high voltage transmitter • Allows us to enjoy television, automobiles, and just about every other electronic device • Wireless electrical transmission • X-rays, radio, wireless telegraphy all attributed to Nikola Tesla • http://www.youtube.com/watch?v=pBx2wkg9nhk

  26. Lightning LIGHTNING

  27. Lightning • Lightning can travel up to 140,000 mph • Produce temperatures of 54,000°F • Can form fulgurites (sand into glass) • Transfers 15 C of electric charge

  28. What is lightning? • A natural capacitor • Charges are polarized within a cloud • The top of the cloud becomes positively charged • The bottom of the cloud becomes negatively charged • The electric field induces a movement of electrons from the cloud down toward Earth

  29. Lightning Strikes • http://www.teachersdomain.org/asset/phy03_vid_lightning/ • Make a lightning strike • http://environment.nationalgeographic.com/environment/natural-disasters/lightning-interactive/

  30. A lightning strike • The electric field causes ionization of the air surrounding the cloud • This results in a conductive substance called plasma • The lightning bolt begins as a step leader or flow of electrons from the cloud toward the ground • A positive streamer rises up from the ground • When the step leader and the streamer meet, a conductive pathway allows the excess electrons to move to the earth

  31. Lightning Rod • A lightning rod is a protective measure for tall buildings, farm houses, etc. • Used to direct lightning strikes to the ground • This allows the excess electrons to flow into the ground and not into the house or building

  32. True or False • You are safe in a vehicle during a lightning storm. • http://www.youtube.com/watch?v=C8xt9AP41-A

  33. Capacitance • Electrical energy can be stored in a device called a capacitor • Capacitors are found in nearly all electronic devices • Televisions, camera flash, computer • A capacitor must be charged • A capacitor is discharged when a conducting path is provided between the plates

  34. Capacitors • A device that stores charge • Made of 2 conductors separated by an insulator

  35. The charge stored will SHOCK you if you are in the conducting pathway!! • Found in many electrical circuits- computers, televisions, camera flashes

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