Electrostatics and Circuits

1. Electrostatics:

1. Electrostatics

   1. The study of electric charges that can be collected and held in one place.

   2. neutral surface & neutral surface = no electrostatic force

2. Static electricity

   1. Static electricity is caused by an imbalance of + & - charges within an atom

   2. Electrons & protons have same magnitude of charges but not same mass

      1. Protons are ~2000x the mass of electrons 

      2. electrons can move more than protons when acted on by an equal force b/c it has less mass & greater acceleration

3. electric charge

   1. When a charged material touches another material it will gain or lose electrons 

4. Polarization

   1. Separating of charges within an object

   2. EX: after rubbing a balloon on your hair it becomes negatively charged, when the - balloon is put on a neutral board it becomes polarized. The negative balloon attracts the protons to the surface of the board touching the balloon and the electrons move to the other side of the atom. 

5. Charging

   1. How does a plastic strip become negatively/positively charged by rubbing?

      1. Rubbing a plastic strip = friction 

      2. If friction provides enough energy = electron transfer

      3. The other material should have a lesser electron affinity than plastic strip = gain electrons

      4. The other material should have a greater electron affinity than plastic strip = lose electrons

   2. Conduction

      1. direct  contact

      2. Actual transfer of electrons

   3. Induction

      1. Not direct contact = charged object brought near neutral object

      2. Separation of Charges- charges rearranged (positive and negative charges separated)

6. Coulomb's law

   1. F=kq_1q2r2

   2. k= 8.99 109Nm2c2

   3. Describes the strength of electrostatic forces between two forces, attracted or repelled. 

   4. If the value of the force is positive the two forces are repulsive b/c same sign and if the force is negative they are attractive b/c different signs

7. electric field

   1. E=Fq

      1. Base units e=n/c

   2. Vectors

      1. quantity that show magnitude and direction of the electric field in a specific spot in space

      2. multiple  arrows

      3. electric field vectors are in the same direction as electrostatic force vector when q is positive

   3. field lines

      1. Positive field lines go outward(repel)

      2. Negative field lines go inward(attract)

      3. More of a visual/hypothetical

      4. one  arrow

      5. The proximity of field lines to one another tell you how strong the electric field is

4. Electric field between two plates

8. electrostatic potential energy

   1. The amount of energy it takes to move a charge in an electric field

   2. Work increases electrostatic potential energy

   3. ΔPE_E=Eqd

   4. When a proton is transferred electrostatic potential energy is positive meaning it is increasing, for electrons it is negative meaning its decreasing

9. electric potential

   1. ΔV=kqr

   2. ΔV=Ed

   3. does not depend on the transferred charge

   4. 1. A: the spring has more elastic PE when compressed B: similarly the small charge has more PE when pushed closer to the charged sphere. The increased PE is the result of work input

II. Circuits: a closed path for charge

1. electric current

   1. I=qΔt

2. Ohm's law

   1. V=IR

   2. Relationship between voltage across and current through a battery

3. series & parallel circuits

   1. Series circuits: 

      1. Single Path (electrons have no choice)

      2. Current flows through all resistors

         1. Current of resistors & battery are equal

         2. Sum of the voltage of resistors are equal to the voltage of the battery

   2. Parallel circuits:

      1. Multiple paths (electrons have a choice)

         1. A partial amount of electrons choices in their paths 

         2. Voltage of resistors & battery are equal

         3. Sum of the current of resistors are equal to the current of the battery

4. Parts of Circuits

   1. Electrolytic Cell

      1. made of an electrolyte or salt solution

      2. side w/ bump= +, flat side = -

   2. Battery

      1. Combination of electrolytic cells

      2. 1. long side = positive & short side = negative b/c electrons less mass

   3. Resistor

      1. a two terminal electrical component that regulates the flow of electric current

      2. there is a different code on every resistor

         1. R=AB10C+D%

   4. Ammeter

      1. Measures current amperes

      2. Connected in  series with the element you want to measure (can be anywhere in a series circuit) 

   5. Voltmeter

      1. Measures voltage 

      2. Connected in parallel with the element you want to measure 

   6. Node

      1. Area in a circuit where there is only one element (wire)

5. equivalent resistance

   1. Series

      1. eq>largest resistor

      2. R_eq= R₁ + R₂ + R₃ 

   2. Parallel

      1. eq<smallest resistor

      2. 1/R_eq= 1/R₁ + 1/R₂ + 1/R₃ 

6. electric power

   1. The rate at which energy changes

   2. Battery adds energy & resistor takes energy 

      1. P_b= P₁ + P₂ + P₃

   3. P = IV

   4. Resistors only: P = v2R=I2R