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by: kkaizersalk

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# Physics: Electrostatics/Electrodynamics

Marketplace > University of California Santa Barbara > > Physics Electrostatics Electrodynamics
kkaizersalk
UCSB

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Study guide that covers all key information for new MCAT!
COURSE
MCAT
PROF.
TYPE
Test Prep (MCAT, SAT...)
PAGES
7
WORDS
CONCEPTS
Physics, Electrostatics, Electrodynamics, MCAT
KARMA
75 ?

## Popular in Department

This 7 page Test Prep (MCAT, SAT...) was uploaded by kkaizersalk on Thursday March 10, 2016. The Test Prep (MCAT, SAT...) belongs to at University of California Santa Barbara taught by in Winter 2016. Since its upload, it has received 27 views.

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Date Created: 03/10/16
Electrostatics Electric charge - measured in coulombs (C) - e = 1.6 x 10 -19C - charge is quantized: Q = n(+/-e) Electric FE= k Force: Co9lo·b’2 L2w - k 0  Q 1 2 = 9 x 10 N m / C - Trends: r2 o when Q do1bles, F doubEes o when radius (r) halves, F inEreases by exponential amount - Coulomb’s law is analogous to Newton’s Law of Gravitation (*F is E much stronger force than gravitational force) Superposition - Net electric force on a charge (q) due to collection of other charges (Q’s) is equal to sum of individual forces that each of Qs alone exerts on q  add forces as a vector sum Electric Fields E = F = k - Force per unit charge  Q - Vector field - Always points away q from positive source charges and toward r2 negative ones - Charges creating the electric field is/are the a = F = source charge(s) qE m Conductor - Contains charges that m are free to roam throughout the material Insulator - Dielectric: electrical insulator that can be polarized by an applied electric field o When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization. o - Material that lacks free charges - Rubber, glass, wood, paper, plastic Electric Potential  = kQ/r [Units: J/C] ∆PE = q∆ = ∆KE = -∆PE - Electric Potential: potential energy per unit charge - Scalar field (like energy, work, or speed) - (+) Positive charges want to move to regions of lower potential - (-) Negative charges want to move to regions of higher potential Electric Potential Energy Change in Electrical Potential Energy - V = change in potential, known as the voltage Work Done by Electric Field W by electric field -∆PE electric Electric Circuits Current - net movement of charge I = Q/t (C/s) Voltage - Potential difference - Creates current Resistance R = V/I (V/A = - Resistor: component in electric circuit that has a specific Ω) resistance - Resistors in Series: o R eq= R 1 R …2 o R totill always be larger than the largest resistor! o V tot V R1+ V R2+ …. ΣV each= V sys o I tot IR1= IR2= …. - Resistors in Parallel: o R eq= (R1R 2/(R1+ R 2 → can only use for 2 resistors o 1/R eq = 1/R1+ 1/R +2…. o R will always be smaller than the smallest resistor! tot o V tot= VR1 = V R2= …. o Itot= IR1+ IR2+ … - Resistivity: intrinsic resistance of material () R =  L/A - Kirchhoff’s Laws: o The ∑ of the voltage drops across the resistors in any series = V of the battery o The ∑ of the current passing through individual resistors in parallel = I entering the combination Direct Current (DC) Circuits - Consists of a voltage source, connecting wire, resistor - Note: the direction of the conventional current is opposite the flow of electrons! o Negative terminal: terminal at lower potential, denoted by shorter line o Positive terminal: terminal at higher potential, denoted by longer line o Direction of current is taken to be direction that positive charge carriers would flow, even though actual charge carriers that do flow might be negatively charged - Working backwards: a) Series resistors  all resistors share the same current (I = constant)  Voltage may be different b) Parallel resistors  all resistors share the same voltage (V = constant)  Current may be different Alternative Current (AC) - generates sinusoidally varying voltage - at a frequency of 60 Hz (60 cycles/sec) - when voltage is greater than zero (V>0), current is going in one direction, and when voltage is less than zero (V<0) current is going in the opposite direction Power a) Power dissipated by resistor: rate at which resistors dissipate heat energy 2 P = I R  in watts (J/s) b) Power supplied by voltage source: total power dissipated by resistors P = IV  in watts (J/s) 2 (1)V = IR, so P = IIR  V = I R (2)Can use P = IV to calculate power dissipated by resistor, but use for only 1 resistor at a time (best to use P = I R if calculating power for entire circuit) - Power follows law of conservation of energy: power dissipated = power supplied Energy = Power * x Time ***For AC Circuits: Irms= Imax/2 = RVrmso= vgmax√2 = RMS Current V/√2 P = I/√2 Average 2 power dissipated by a resistor: I rms Average power supplied by the voltage P = source: rmsVrms Measuring Circuit Values - Voltmeters - Ammeters - Galvanometer Capacitors C =  0 Q = CV (C/V PE = ½ V = = F) QV A/d Ed - Capacitor: pair of conductors that can hold equal but opposite charges, net charge = 0 - Capacitance: proportionality constant, C - Charge on capacitor occurs because current flows from battery source to the opposing sides of the capacitor a) Q = CV  Q is the charge on the capacitor, C is the constant (capacitance) - Parallel Plate Capacitor - 2 main uses: o Create uniform electric field   constant in magnitude and direction throughout region between plates o Store electrical potential energy (∆PEelectric) - Capacitance of Parallel Plate Capacitor – how much charge can be stored at a certain voltage o C =  A0d   = c0nstant o  0 = permittivity of free space = 1/4πk 0 o Note: capacitance is directly related to area, inversely related to distance (the closer the plates are, the greater the force between them and therefore more charge can be stored) - Electric Fields in Capacitors – very straightforward o V = Ed  strength of E depends on voltage and distance between plates o Units are neither N/C or V/M, same thing - Electrical PE Stored in a Capacitor o PE depends on voltage between plates o PE = ½ QV  Q = CV, rewrite PE = ½CV = ½ Q /(2C) 2 o As Q so should PE! - Discharging Capacitor o Capacitors discharge on their own, nonlinear (most happens at beginning) - To increase () charge (Q) in capacitor, work is required to remove electrons from the (+) plate and move them to the negative (-) plate  this work against the electric field is stored as electric potential energy (PE )E Dielectrics - Dielectric: insulating material/slab between plates of capacitor  increases capacitance o Prevents plates from touching and discharging o Can hold Q, and thus PE E - Dielectric constant: K – factor that capacitance is multiplied by if dielectric is present o never less than 1 o K tells us how much the dielectric increases capacitance Capacitance of a Parallel-Plate Capacitor with a Dielectric C = K C = with dielectric without dielectric K 0/d Effects of Dielectric on C, V, Q, E, PE E - Charge capacitor, then disconnect battery and insert dielectric: (1)C (by K) according to equation (2)Q remains the same, since the charges on the capacitor still can’t go anywhere (3)V (by K) because Q = CV (Q same, C by K,  V by K) (4)E (by K) because V = Ed (V by K and d same  E by K) (5)PEE (by K) because PE = E QV (Q same, V by K,  PE  by E K) - Charge capacitor and insert dielectric while battery is still connected: (1)C (by K) according to equation (2)Q (by K) because Q = CV (C by K and V same,  Q by K) (3)V remains the same because the capacitor plate voltage will equal the battery voltage (4)E remains the same because V = Ed (V same and d same,  E same) (5) PEE (by K) because PE =E½ QV (Q by K, V same PE  by E K) Dielectric Breakdown - electrons can jump the space between capacitor plate under only extreme circumstances - each dielectric has a maximum electric field strength where it will no longer act as an insulator - dielectric breakdown: when the dielectric is ionized and electrons from capacitor travel across (max electric field strength has been exceeded per distance) Combinations of Capacitors - Capacitors in parallel: C eq = C 1 C +2C + 3 o V total V 1 V 2 - Capacitors in series: 1/C eq= 1/C 1 1/C +21/C + …3 o V total V 1 V 2 Magnetism Magnetic Fields and Forces - Field lines emanate from north pole (N) and curl around and re-enter magnet at south pole (S) end - Magnetic Fields: created by moving electric charges FB= q(v x - Magnetic Force: B) o B = magnetic field strength  Units: N/Am = Tesla (T) o v = velocity of charge o Direction of F B is always perpendicular to both v and B FB= |q| - Magnitude of vBsinø Magnetic Force: o Ø = angle between v and B - Charge can be moving through a magnetic field and feel no force if its direction of motion is parallel to magnetic field lines Sources of Magnetic Fields - B created by long, straight current carrying wire: B  I/r - B created by solenoid: B  I (N/L) o L – length of solenoid o N = # coils

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