Electric Fields and Potential Maddie Thomas, Bailey Sprague, Joe Lamberty, & Ashley Williams

State and Explain Major Concept(s) "Electric field is defined as the electric force per unit charge. The direction of the field is taken to be the direction of the force it would exert on a positive test charge. The electric field is radially outward from a positive charge and radially in toward a negative point charge." ( Hyper Phyics.edu ). If you're near a Van de Graaff generator, which is an electrostatic machine, you could feel the charge. "The space that surrounds each of these things-the magnet, the black hole, and the electric charge-is altered. The space is said to contain a force field" which extends through space ( Physics book). Electric fields have both magnitude and direction which makes it a vector quantity.

Historical Perspective The original research and study of electric fields is largely credited to Scottish physicist James Maxwell. He based his research on the experimental discoveries of Faraday, and was able to provide a mathmatical equation to go along with electric and magnetic fields. Discoveries such as radio waves and X-rays validated his theories and equations.

Application of Concepts The applications of electrical fields and potential would be the Van de Graaff generator which is a common laboratory device used for building up high voltages as a demonstration of electric fields.

Think and Explain Questions 1.An electric field interacts with charge (instead of mass). It can exert repulsive forces as well as attractive forces, and can therefore be shielded. 2.The field lines indicate the direction of force exerted on a positive "test" particle if it was placed in that spot. If you place a test mass above the Earth, it will feel a force toward the Earth. Thus, the field lines around the Earth point toward it. If you place a positive test charge near a proton, it will be repelled away (like charges repel). Thus, the field lines around a proton point away from it. 3.They will travel in opposite directions and the acceleration of the electron will be greater than the acceleration of the proton. 4.It will be ¼th the strength in accordance with an inverse square law. 5.Like charges repel. Since this is a conductor, excess charge is free to move. The electrostatic potential energy is minimized when the excess charge is distributed for the smallest average of 1/r. For a spherical surface this results in a uniform charge distribution on the surface. 6.The pointy places like the corners will have more charge concentrated there because the electric field will be higher at the points. This is how a lightning rod functions, concentrating the charge and intensifying the electric field. The metal surface is at equal potential. Remember the potential near a spherical surface is proportional to 1/r. The electric field is proportional to the derivative of the potential, or is proportional to 1/r^2. If the radius of curvature is small, ie pointy surface, then the electric field is high. 7.a Volts b. 12 J; conservation of energy 8.a Volts b. 24 J (same as the work done on it) 9.Only if it has the same charge 10.Strands of hair are charged with the same sign of charge and are mutually repelled.

Review Questions 1. It is the interaction between things physically apart. 2. There is contact between the thing and the field. 3. Both are means of exerting forces. 4. It has magnitude and direction. 5. a. Lines depicting the electrical field. b. They are the same. 6. Closer lines means a stronger field and further apart means a weaker field. 7. The lines are parallel and equally spaced between the two parallel plates. 8. Charge is on the outside and the field inside cancels to zero. 9. The electric field inside any charged conductor is zero. 10. a. No. b. Yes 11. Work = potential energy. 12. By doing work on it against an electric field. 13. The potential energy will convert to kinetic energy. 14. Electric potential is electric potential energy divided by the charge. 15. Increase electric potential energy and charge and leave the same. 16. Volt 17. No 18. A small charge has a high number. 19. Inside has zero, all charges repel to outside million volts.

Framing the Demonstration "Electric field is defined as the electric force per unit charge. The direction of the field is taken to be the direction of the force it would exert on a positive test charge. The electric field is radially outward from a positive charge and radially in toward a negative point charge." ( Hyper Phyics.edu ). If you're near a Van de Graaff generator, which is an electrosatic machine, you could feel the charge. "The space that surrounds each of these things-the magnet, the balck hole, and the electric charge-is altered. The space is said to contain a force field" which extends through space ( Physics book). Electric fields have both magnitude and direction which makes it a vector quantity.

Question or Hypothesis You are Investigating How lose does the compass need to be to be effected by the electric field?

General statement of how you will conduct the demonstration We will place a compass near and inside an electric field and record the effects the field has on the magnetized needle of the compass.

Apparatus and Materials Needed Compass Power Supply Complete Circuit Ruler

Step-by-Step Instruction for Doing the Demonstration 1. Create a circuit 2. Power the circuit with the power supply 3. Move Compass towards the circuit until the compass needle moves 4. Measure the compass's distance from the circuit 5. Record the distance

Safety Precautions Don’t electrocute yourself

Tables of Results Distance at reaction cm

Analysis of Results The compass needs to be within 20.2 cm of the electric field to be effected by the electric field.

Conclusions Supported by Evidence As demonstrated in out expiriment the compass needs to be within 20.2 cm or less to be effected by the electric field.

Evaluation of Your Hypothesis to Answer Your Question The compass needs to be within 20.2 cm of the electric field to be effected by the electric field.