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Physics Exam
| Question | Answer |
|---|---|
| Electric Charges | - 2 Types: (+) & (-) - Like charges repel while opposite charges attract - Quantized, Conserved & measured precisely - Creates Electric Fields |
| Electric Fields (E) | - Electric Field vectors point away from (+) Qs but toward (-) Qs - Symmetry (Uniform/Even & Center at Origin) Cancels Perp. Es (E=0) - Always points in the direction of decreasing electric potential |
| Small Test Charge (q) | - (+)q: Force & E -> in the same direction (Outwards q) - (-)q: Force & E -> in the opp. direction (Inwards q) |
| Atoms | - Electrically neutral - Neutron (+0) No mass |
| Law of Conservation of Electric Charge | - If an object acquires a (+) charge, then an equal amount of (-) charge will be found somewhere else. Vice Versa - Net Electric Charge produced in any process is always 0 |
| Charges with Electric Force | - Charges decide the action - Pull charges along the axis arrow, (+) force - Pts opps. to the axis arrow, (-) force |
| Superposition | Add the vectors up - Electric fields obey Superposition just like forces |
| Electric Field Lines | Lines show the direction field vectors pt - The # of lines is proportional to the charge | Ex: +1 charge has 2 lines & +2 charge has 4 lines - Closer the lines, stronger the field |
| Electric Potential | Energy that can become something else - Only the potential energy difference with 2 pts is measurable - Amount determines the energy in a gravity/electric F change - Bigger G/E PE = bigger mass /charge |
| Electric Potential With Charges | V = Change in electric potential - (+) Charges accelerate: Move from higher to lower V - (-) Charges accelerate: Move from lower to higher V - Is independent of the test charge |
| Electric Potential & Force With Work | Electric Force does (+) Work - Charge gains kinetic energy - Potential energy of the charge decreases |
| Electron Volt (eV) | Energy acquired by an electron moving through a potential of 1V - Used for atomic energy transitions |
| Equipotential Surfaces | - No work is done by electrical forces when moving along an equipotential surface - Electric field is always perpendicular to the Equipotential Surface |
| Dielectrics | An insulating material placed between capacitor plates - Permittivity of Space: Has a dielectric inside the space - Permittivity of Space > Permittivity of Free Space - Specific k constant (Problems will tell u the value) |
| Polar Dielectric & Induced Dipoles In Dielectric Materials | - PD: Molecules with a perm. electric dipole moment (Shows random orientation) - ID: Has an E, produces partial alignment of the dipoles (Thermal agitation prevents it fully) - Neutral molecules can have a dipole moment |
| Circuits | Closed path which allows electric current (-e) to flow | Needs a power source - Voltage Source: An electromotive force (EMF/E) maintains a constant PE between its terminals - Elements are connected by conductors/wires |
| Static Electricity | Charges don't move but stay put at the location they are placed |
| Conductors in Static Equilibrium | - Circuits are equipotential - No voltage drop/rise along a conductor - No electric field inside a conductor (E=0) |
| Conductors Not in Static Equilibrium | - voltage drop/rise along them is negligible - E around = 0 |
| Capacitors | A device that can store charge but doesn’t let them flow through - Consist of 2 conducting objects (plates/sheets) placed near each other without touching (B/c charge will neutralize) - Battery: PE difference by storing energy while C stores charges |
| Parallel Capacitors | Elements have same potential | Differ. Circuit but same position - Has the same Voltage (V) but different Charge (Q) |
| Series Capacitors | Elements are in the same circuit with no junction between them - Has the same Charge (Q) but different Voltage (V) - Smaller capacitors get a larger voltage drop |
| Resistance | - Electrons will accelerate until reaching terminal velocity - Current is proportional to PE (V) when R is constant - Wire is a cylinder, so cylinder Area |
| Parallel vs Serie Resistors | Parallel Resistors: Series Capacitors - Has the same Voltage but different Currents Series Resistors: Parallel Capacitors - Has the same Current but different Voltages |
| Determine the equivalent capacitance, resistors & charge on each Capacitor | - Find capacitance/resistors separately (Series & Parallel) then add together (Series + Parallel) - Find Charges separately for Parallel C & together for Series C |
| Current (I) | Movement of charges (Not Static Equilibrium) - PE placed across a conductor creates an electric field → Causes charges to move |
| Different Types of Current | - Direct Current (DC): Current always flows the same direction - Alternating Current (AC): Direction of current flow changes periodically - Conventional Current: Made up flow of (+) Charges |
| Battery: Terminal Voltage | Modeled by a series combination of an EMF (voltage source) & a resistor (internal resistance) - Battery goes bad: r becomes BIG - Battery is drained: Curved E drops |
| EMF | Sum of voltage drops across the capacitor & resister - All resistances (Even Internal resistance) |
| Resistors | A device with BIG resistance (Heartbeat) - Conductors’ resistance is VERY low (Dead Heartbeat) - Current flows from high potential to low potential through a resistor |
| Resistance Changes With Length & Width | Block: Length & Cross-Sectional Area (A) - Length = V & Width = I - (Made Up) N = Number of Blocks |
| Resistance Changes With Length & Width: # Blocks On Top of Each Other | - Increases Area (I) but decreases Resistance (R) - Ex: 2I: Doubles area & resistance decreases by a factor of 2 |
| Resistance Changes With Length & Width: # Blocks After The Other: | - Increases Length (V) & Resistance (R) - Ex: 2V: Doubles length & resistance increases by a factor of 2 |
| Resistance Changes With Length & Width: Adding a Constant | Add a constant & the proportionality becomes equality - ρ: Resistivity - Conductors: ρ = 10^-8 Ωm - Insulators: ρ > 10^10 Ωm |
| Temperature & Resistivity: Temp. Coefficient of Resistance | α: Measures how much a material's R changes with temp. change - α is ONLY valid for a given value of T0 - ρ(T) = Resistivity at Temp & R(T) = Resistance at Temp |
| Superconductors: When T < TC | Superconductor: A conductor loses all R (ρ → 0) & temp < Critical Temp (TC) - Critical Temp is the tipping pt where a material changes from a normal conductor into a superconductor |
| Kirchhoff’s Rules: 1st Rule: Junction Rule (Charge Conservation) HELP | |
| Kirchhoff’s Rules: 2nd Rule: Loop Rule (Energy Conservation) HELP | |
| Ammeter | Measures current - Placed in Series (so current flows through it) since blows a fuse in Parallel - Very low resistance (so not to affect the current it measures) |
| Voltmeter | Measures voltage - Placed in parallel - Very high resistance (so little current flows through it) - Ideal Voltmeter: I = 0 ,so just reads V |
| Multimeter | Measures voltage, current, or resistance |
| EMFs in Series: | - Same Direction: Total voltage is adding their voltages - Opp. Direction: Total voltage is subtracting their voltages |
| RC Circuit | Circuits containing both resistors & capacitors - Look: EMF, capacitors, & resistors |
| RC Circuit: When Switch (S) is Closed: | - Current flows immediately, causing (-es) to add up on the capacitor's plates & building up its PE differ. - As the capacitor charges toward its max capacity (C), the current gradually drops to 0 once the capacitor's V = EMF |
| EMF's Terminal Electrons | - EMF’s (-) Terminal Electrons: Adds up on capacitor’s upper plate - EMF’s (+) Terminal Electrons: Adds up on Capacitor’s bottom plate |
| Capacitor’s Charge & Current vs Time Graph | - Capacitor’s Charge vs Time Graph: Increasing through Time - Capacitor’s Current vs Time Graph: Decreasing through Time |
| How to Find Min & Max Capacitance | - Min Capacitance: Connecting all capacitors in a Series - Max Capacitance: Connecting all capacitors in a Parallel |
Created by:
Whateverisfree
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