Physics 2 Flashcards

Question

* Electromagnetic Spectrum * Describe Visible Light * λ=? * Describe RED light (3) * Describe Violet light (3) * Mnemonic=?

Answer 1

* ***390-700nm*** * ***RED*** *LIGHT* 1. ****lowest** energy 2. **lowest** frequency 3. **longest** λ * ***VIOLET*** *LIGHT* 1. ****highest** energy 2. **highest** frequency 3. **shortest** λ * Mnemonic: * ROYGBIV

Answer 2

* **F_m=mg (h/d)** * h=height of ramp * d=distance along its hypotenuse * F_m=force necessary to do the work *with* the machine * "5 meter ramp" or "5 meters long" * implies that the _***hypotenuse*** _of the ramp is 5m

Answer 3

* Formula * V=IR * Common error: * it ***CANNOT*** be said that if voltage **increases** and current remains **constant** that resistance will ***INCREASE*** * Resistance is a permanent quality of the resistor *itself* * The only way to change resistance is to: 1. *physically replace* resistors with resistors that have different Ohm's ratings, or 2. change the temperature of the resistor

Answer 4

* *Energy in an **ISOLATED** system is always **CONSERVED*** * Energies (KE, PE, Heat Energy, etc.) are frequently ***transferred*** back and forth, but ***NEVER LOST ***

Answer 5

* **g** (stength of grav. field) * =**E** (strength of electric field) * **G** (constant) * **K** (constant) * **h** (distance) * =**r or d** * **m** (mass) * =**q** (charge) * **F** (force) * =**F** (same in both) * **gh** (PE_grav) * =**V** (voltage, PE_electrical)

Answer 6

* **P=1/f**

Answer 7

*a dipole is a **separation** of positive & negative charges of **EQUAL magnitude*** When a dipole is exposed to an elec. field, it tends to ***align itself** with that field* * ***a dipole that is _NOT aligned_ with the elec. field has PE*** * ******alignment with the field is a **lower energy state** than alignment ***AGAINST*** the field

Answer 8

* The Universe always has a ***ZERO net charge*** * Charge is created by separation * If you separate one electron from a neutral atom, you have created: * one independent unit of **negative charge** (the electron) * and _simultaneously_ created one independent unit of **positive ****charge** (the cation)

Answer 9

* Always drawn with their ***tails*** at the ***positive*** charge * Pointing *AWAY FROM*, or * Pointing *TOWARDS* the ***negative*** charge * ***CLOSER LINES=STRONGER FIELD*** * Field Lines best approximate *Current Flow* * Current flows from **positive to negative** concentrations **ELECTRON** Flow is the ***opposite*** (neg.⇒pos.)

Answer 10

* Transverse waves * displace the medium ***perpendicular to*** their direction of travel * ex: EM waves, waves on a string * Longitudinal waves * displace the medium ***parallel to*** their direction of travel * ex: sound waves, p-wave earthquakes

Answer 11

* Elastic property: "Bulk Modulus" (B) * Inertial property: Density, ρ * Although the *densities* of solids are typically ***thousands of times higher*** than the densities of gases... * the elastic moduli are even increased ***by an even LARGER factor!!*** * This property causes solids to ***“spring back” extremely quickly*** following deformation. * Sound (compression) waves in solids are therefore ***TYPICALLY _MUCH FASTER_ THAN SOUND WAVES IN GASES .***

Answer 12

1. **P=ΔE/t** 2. **P=W/t** 3. **P=Fscosθ** 4. **P_i=Fvcosθ** * gives "**instantaneous** power" * should only be used when asked for *specifically* * **Units: **Watts** * J/s

Answer 13

* Wavelength (units = meters) * distance between two adjacent: * crests (a.k.a., peaks, maxima), * troughs (a.k.a., valleys, minima). * Period and frequency are ***ALWAYS _INVERSES_ OF EACH OTHER!!*** * Velocity * ***how fast*** the wave moves _in space_ (in m/s). * given by v = fλ. * Amplitude * the “distance” between: * the equilibrium point and a crest, or between the equilibrium point and a trough. * Intensity is * a measure of power per unit area. * Waves have power because they transport energy from one point to another in a given amount of time. * Intensity is proportional to the ***square of the amplitude*** and the ***square of the frequency.*** * Phase * is a relative measure of ***how closely two waves*** (typically with the same frequency) ***are oriented to one another in space***, * typically expressed in *radians* or *degrees*. * Two waves that are “in phase” should cross the x-axis **at the same point**, but _may have different amplitudes_

Answer 14

* Young shone a monochromatic light through a screen with a single slit in it. * The purpose of this slit was to **create coherent wavefronts** * Behind the first screen he placed a second screen ***with two narrow, parallel slits.*** * These created the *diffraction* pattern. * Finally, behind the second screen he placed a *third* screen. * Light traveled through the first two screens and formed alternating pattern of ***LIGHT*** and ***DARK*** bands on the third screen. For the experiment to work, the light traveling through each of the 2 slits in the middle screen *must be coherent* and have the ***SAME FREQUENCY & POLARIZATION***

Answer 15

* ***FIELD=*** *an invisible **influence** capable of **exerting a FORCE** on a:* * *mass, or* * *charge*

Answer 16

1. W=Δ *Energy* 2. W=Fdcosθ * If ***ENERGY*** changed, think ***WORK!***

Answer 17

* Near-sighted (myopia) * able to focus clearly on ***CLOSE*** objects, but not on distant ones * The image is ***IN FRONT OF*** the retina * Far-sighted (hypertropia) * able to focus clearly on ***DISTANT*** objects, but not on close ones * The image is ***BEHIND*** the retina

Answer 18

**_The Wave Model of light_** supposes that light is a **wave** * **Young’s Double Slit Experiment** provides support for this model * because only waves would show the **diffraction** and **interference** patterns necessary to create the characteristic **light** and **dark** bands **_The Particle Model of light_** supposes that light is a **particle** * **The photoelectric effect** is the major support for this model. * Says that electrons are ejected from a material when light of ***sufficiently high frequency*** is used— * but ***NOT UNTIL*** a threshold frequency is reached. *_The two are reconciled by:_* ***_QUANTUM MECHANICS!_*** photons are ***described by “wave functions”*** which sometimes act as * macroscopic ***waves***, and sometimes as * macroscopic ***particles***

Answer 19

* In order to be **100% in phase**, two waves would have to have the same: **1) Frequency**, **2) Wavelength** and *most importantly* **3) TIMING OF MAXIMA/MINIMA** * which could be done if they share the **same time/place of origin**)

Answer 20

* **E=hf** * h=Plack's constant (given)

Answer 21

1. ***REQUIRE A MEDIUM*** to propagate 2. Transfer ***ENERGY ONLY!!!*** (not momentum) Can be ***BOTH*** transverse & longitudinal 1. Transverse * transverse mechanical waves require a fairly ***STIFF MEDIUM*** in order to propagate * ∴ ***cannot*** propagate in **liquids** or **gases** * ex: strings on a musical instrument 2. Longitudinal * ex: sound waves

Answer 22

* The energy contained ***within chemical bonds*** * Or the energy ***stored/released*** due to the separation and/or flow of ***ELECTRONS*** * i.e. a battery

Answer 23

1. ) Voltage =Potential Energy ***DIVIDED by _charge_ or _mass_*** 2. ) Voltage= whatever "thing" you can ***MULTIPLY by mass or charge*** to get Potential Energy * Examples: * gh\*m=mgh=*PE_{gravitational}* * Ed\*q=*PE_electrical*=V\*q

Answer 24

* **Radio** waves * 10³ * **Micro**waves * 10^-2 * **Infrared** waves * 10-5 * **Visible** Light * 10^-6 * **Ultraviolet** light * 10^-8 * **X**-rays * 10^-10 * **Gamma** Rays * 10^-12

Answer 25

*is a rating system for the intensity of sound **within the range of human hearing*** Both it and the Richter scale use ***logarithmic scales*** * Difference: _In short:_ ***10x** increase on Richter Scale = **1 unit increase*** ***10x** increase on dB scale=**10 unit increase*** 10x increase in earthquake intensity=*1.0 unit increase on Richter scale* ***10x increase in sound intensity=1_0.0 unit increase on dB scale_*** * a sound 10x more intense is ***10dB higher*** * a sound 100x more intense is ***20 dB higher*** * a sound 1000x more intense is ***30 dB higher***

Answer 26

* Resistors * in series: * add directly * in parallel: * add the inverses * take the inverse of *that* sum * Capacitors ***(o******pposite of solving for resistors)*** * in series: * add the inverses * take the inverse of that sum * In parallel: * add directly * Batteries * in series: * add directly * in parallel: * ***TOTAL voltage= ***the ***HIGHEST*** voltage of *any one of the batteries in **parallel***

Answer 27

* Transverse vs Longitudinal * EM Waves * Mechanical Waves

Answer 28

All objects have one or more ***natural frequencies*** *at which they will vibrate when disturbed.* * Some objects produce a **random** array of different vibrational frequencies. * Other objects (i.e., musical instruments) vibrate at ***non-random natural frequencies*** * ******which are integer multiples of a number (e.g. 200Hz, 400Hz, 600Hz, 800Hz). * These orderly frequencies are called "***HARMONICS"***

Answer 29

1. Change in **VELOCITY** * change in KE=work! * ***most common example!*** 2. Change in **HEIGHT** * change in PE_grav = work 3. Change in **POSITION** (of **masses**/**planets**/etc.) **IN SPACE** * change in PE_grav = work 4. **COMPRESSION** of a spring * change in PE_{elastic = work} 5. **FRICTION** * change in internal energy=work 6. **AIR RESISTANCE** * change in internal energy=work ***_CAVEAT_:*** Energy transfer in a system ***could** be due to **Heat Transfer** as well!!* * **non**-conservative forces dissipate some heath energy * this leaves ***LESS*** energy available to do work * Use of word "heat" refers to *an **increase** in the* ***internal energy* of the molecules, NOT**"heat transfer" ('Q' from the first law of Thermodynamics).

Answer 30

The harmonics shown below are all for a single vibrating guitar string of the ***same length*** * Notice: * the 1st harmonic is only **½** of a **λ** * the 2nd harmonic is **EXACTLY 1 λ** * the 3rd harmonic is **1½** **λ**

Answer 31

Intensity= ***POWER per unit area*** *Units: Waves/m²* * Waves often have power (often called "sound power") * because they *transfer energy from one location to another w/in a specified time* * (aka, energy flux) _In *sound or **mechanical** waves,* Intensity is ***DIRECTLY PROPORTIONAL TO:***_ * **AMPLITUDE ²** * **FREQUENCY²** _******In **LIGHT** waves***,*** intensity is directly proportional to:_ * **AMPLITUDE²** But ***NOT (!!)* FREQUENCY²**

Answer 32

Think of this definition ***second*** (First should be W= Δ in energy) * Any time a ***force is applied across a displacement,*** _work_ has been done _Units: **Joules, aka:**_ * N\*m * kg\*m² /s^-2

Answer 33

* Many waves (such as sound) travel outward from their origin **in ALL directions SIMULTANEOUSLY*** * ...which creates a wave front in the* * shape of a growing sphere* Magnitude of Intensity ***DECREASES*** according to **AREA** of the growing sphere * b/c **intensity** is measured *per **square meter*** _**IN**creasing **m²** leads to a **DE**crease in **Intensity**_ (ODI) * **A=4πr²**

Answer 34

Voltage=the amount of PE a system is capable of storing per unit charge **V=PE_sys/q** * Another way: * Voltage=the amount of work necessary to **move** a charge ***against the electric field*** * moving a **longer** distance requires **more** work (voltage **increases** with distance) Formulas: * **V=Ed** * **V=Kq/r**

Answer 35

The "dialectric" is the ***substance BETWEEN the two plates*** * ***ALL** capacitors* have a dialectric, ***even if it is just air*** * Other dialectrics=gel, composites, etc. * once inserted, some energy stored in the capacitor is used to align the polar molecules in the dialectric (ie, dipoles) with the field between the plates * Increasing the strength of the dialectric ***increases the capacitance*** * ******allowing more charge and energy to be stored ***INCREASING dialectric=INCREASING capacitance*** * The dialectric must always be an ***INSULATOR.***

Answer 36

1. The variable ***v*** is ***RELATIVE*** velocity * ***NOT*** the velocity of either object 2. The variable ***c*** is the ***speed of the wave*** * 3 x 10⁸ m/s for light * 340 m/s for sound 3. The answer is of the equation is***CHANGE IN λ*** * which is often ***NOT*** what they're asking for!! ***This*** value must be **added** or **subtracted** from the **initial** value in order to get the ***ACTUAL*** value due to the doppler effect 1. Add to the frequency (subtract from the λ) if the relative motion is ***towards*** each other 2. Add to the λ (subtract from the frequency) if the relative motion is ***away from*** each other

Answer 37

* **x=λL/ d** * x=distance b/t fringes * λ=wavelength of light used * d=distance b/t the two slits * L=distance b/t double-slit and final screen * Diffraction * is the tendency of light to ***spread out*** as it goes: * ***around a corner, or*** * ***through a slit*** * *equally as important* as constructive & destructive interference in Young's experiment * without it, Young's characteristic interference patterns wouldnt be formed

Answer 38

* **L=nλ/ 2** * For string or pipe with ***matching ends*** * Both nodes or both antinodes * Gives all nodes * n=1,2,3... * Rearranged: **λ=2L/ n** * **L=nλ/ 4** * ****For *one node* and *one antinode* * Pipe open at ***one end ONLY*** * Gives only the ***ODD harmonics! *** * ******n=1,3,5... * Rearranged:** λ=4L/ n**

Answer 39

* Current flows ***opposite*** to the direction of electron flow * I=Δq/Δt * Current flows from ***positive to negative*** * Electrons flow from ***negative to positive ***

Answer 40

* For waves passing from higher index mediums into lower index mediums, the critical angle ***is the angle of incidence for which the angle of refraction will be 90°.*** * If this angle is exceeded, ***refraction ceases*** and ***all waves are reflected back*** into the more dense medium (Total Internal Reflection)

Answer 41

* are simply ***equlibrium*** problems * To Solve: * set Tclockwise=Tcounterclockwise * Include ***ALL ***torques * including T created by mass of the board * Force due to mass of the board will act as *center of mass* * will always be the exact linear center of a uniform board * Dont forget to set *torques* equal to e/o, ***NOT FORCES!!!*** * units: N\*m * Forces or tensions located ***exactly at center*** of rotation do ***NOT CREATE A TORQUE!! (ignore)*** * ******since r=0

Answer 42

* If a net force does work on a rigid object,** **the work done on that object ***is equal to the change in the KE*** of the object * W= KE_final- KE_initial * ***Focus on ΔE*** * if you think of it this way, there is ***no need*** to use the Work-Energy Theorem

Answer 43

* PE_g= -Gmm/r

Answer 44

1. Nuclei with an odd atomic # or mass # * they exhibit nuclear spin 2. Electrons * because they orbit and spin 3. Current * because it ***IS*** moving electrons 4. Bar Magnets * usually made of nickel, iron, or other alloy * Normally, electrons in a metal are *approximately split* between spin states * In bar magnets, though, they are ***partially aligned***, creating a ***net magnetic field***

Answer 45

* Are drawn ***perpendicular to*** field lines * Represent ***areas of equal voltage*** (i.e. electrical potential)

Answer 46

* Thinking of positive charges as tiny little "things" with an inherent charge * similar to electrons, except positive * This is (essentially) a ***positron*** * ***Protons*** also fit this concept * ***_FORGET ABOUT POSITRONS & PROTONS_*** when it comes to: * ******circuits, electricity, current, etc. * Positive charge is ***ALWAYS:********* * ******a_ ***LACK OF ELECTRONS ***_(relative to being neutral)

Answer 47

* *Voltage drop* across _***THAT*** _resistor=*current* through ***_THAT _***resistor X *resistance* of ***_THAT _***resistor

Answer 48

1. The frequency of the first harmonic is called the ***“fundamental frequency.”*** 2. Each additional harmonic has its own unique *frequency* and *wavelength*. 3. Each harmonic always has one more node, and one more antinode, than the previous harmonic. The frequency of **any** harmonic is equal to: ***n\*fundamental frequency*** * (e.g., if the first harmonic is exactly 200 Hz, the 2nd is 400 Hz, the 3rd is 600 Hz, etc.) For oscillators with matching ends, ***the wavelength of the second harmonic equals:*** ***the LENGTH of the string or pipe (λ= L)***

Answer 49

* For gravity near earth, **V=gh ** * For a constant elec field: * **V=Ed** (d measured against strength of elec field, E) * For "real" gravity, **V=Gm/r** * for a point-charge elec field: * **V=Kq/r**

Answer 50

* Energy change ***is not ALWAYS due to work*** * some energy is lost to/dissipated as *heat* * Work + Heat are the ***ONLY TWO WAYS*** energy can be transferred in/out of a system * ΔE= W+Q * Work=energy transfer *due to a **force*** * Heath=energy transfer *via **energy flow** from Hot⇒Cold*

Answer 51

* the ***gradual loss of intensity*** as a wave passes *through a medium* * * * In non-dispersive mediums, this is ***due to scattering*** (i.e. reflection) ***of some waves*** and ***absorption of wave energy***

Answer 52

* The terms “1st overtone,” “2nd overtone,” etc., are sometimes used. * The 1st overtone is ***NOT the same*** as the 1st harmonic!!!! * The first harmonic is called * _the fundamental frequency,_ * the ***second*** harmonic is called * the ***1st overtone*** * the ***third*** harmonic is called * the ***2nd overtone***, and so forth.

Answer 53

* Magnetism=analogous to ***ELECTRICITY***, with these changes: 1. Replace (+) charges with ***NORTH ***poles 2. Replace (-) charges with ***SOUTH ***poles 3. Magnetic Field lines go from **North⇒South,** *instead* of Positive⇒Negative

Answer 54

* any problem where the object in question has a ***_NON-ZERO_ ACCELERATION*** * *aka _Net Force_ is **NOT** zero* * Solved in the same way as an equilibrium problem, but you ***add "ma"to the _losing side_*** * By adding ma to the weaker side we are making them **equal** again

Answer 55

* Symbol: a diagonal break in the line b/t circuit components * Open switch * ***NO ***electron flow * Closed switch * ***electrons flow***

Answer 56

* T=Fl * T=mgl * T=Frsinθ * when force applied *_isnt_ perpendicular* * *θ _isnt_ 90º* * rsinθ=l, but ***only when θ=90º*** * You can usually just use ***T=Fl***

Answer 57

* capacitors ***store energy and charge*** by holding electrons on plates separated by a very small distance * Symbol: 2 vertical lines of equal length * Formulas: * Capacitance * C=Q/V * PE stored *by a capacitor* * U=½CV² * Solve C=Q/V for the missing variable, then plug it into the above equation * U=½CV²looks a lot like the KE formula!

Answer 58

* Energy dissapated as heat * on the MCAT, this usually is heat dissapated from a: 1. ***collision*** , or 2. ***curent-carrying wire*** * "Heat Energy" ≈ "Internal Energy"

Answer 59

* _Increasing plate area_ ***increases*** capacitance because there is more room available on the inside surface of the plate to store electrons. * Electrons do not line up on the sides or back of the plate, so _increasing plate thickness_ will have ***no effect*** on capacitance. * _Increasing the distance between the plates_ increases voltage for a given Q on the plates, which ***decreases*** capacitance according to C = Q/V. * _Increasing the strength of the dielectric_ ***increases*** capacitance because the dielectric impedes the buildup of the electric field between the plates and diverts some of the capacitor’s finite energy storage capacity to realign dipoles inside the dielectric. * _Increased voltage_, increases the charge stored but ***does not increase capacitance,*** which is the charge stored per voltage.

Answer 60

* Pitch is the ***"perception" of frequency*** by the human _ear_ * Closely related to frequency, but ***NOT IDENTICAL*** * Is a musical (not scientific) term * Sounds with ***HIGHER PITCH*** have: * *********higher frequencies*** * ******Sounds with ***LOWER PITCH*** have: * ***lower frequencies***

Answer 61

* For gravity *near earth, ***g=F/m** (from F=mg) * for a constant elec field: * **E=F/q** (or **E=V/d**) * For "real" gravity, **g=Gm/r² ** * for a point-charge elec field: * **E=Kq/r²**

Answer 62

* The lens of the human eye ***is a converging lens***. * It creates a **real (inverted)** image of the object onto the retina. * A magnifying glass is ***also a converging lens***

Answer 63

* If the Dopper Effect causes an ***INCREASE*** in frequency (or ***DECREASE*** in λ): * *White light* shifts ***BLUE*** * If the Dopper Effect causes an ***DECREASE*** in frequency (or ***INCREASE*** in λ): * *White light* shifts ***RED***

Answer 64

* is a special case of simultaneous ***CONSTRUCTIVE _AND_ DESTRUCTIVE*** interference b/t 2 waves * have ***identical*** frequencies moving through the *same medium* in ***opposite*** directions * At points of maximum destructive interference, waves ***cancel entirely*** to create a "node" * At points of maximum constructive interference, the waves ***ADD completely*** to form an "anti-node" * Result: * is a waveform in which the areas b/t the nodes appear to ***OSCILLATE up & down*** b/t crests and troughs * A standing wave exhibits ***NO net transport of energy,*** and does not ***itself*** propagate * basically, theres no translational mvmt of nodes or anti-nodes in *either* direction * When a standard ***Traveling*** wave propagates, the minima & maxima move translationally in the direction of propagation

Answer 65

1. Point Charge Fields * equate to "real" gravity, or **gravity in space** * A point charge field is an electric field **created by a point charge** * The strength of the electric field ***varies with the distance (r)*** from the point charge. 2. Constant Electric Fields * equate to "assumed" gravity, or **gravity near earth** * is *constant* * its strength does ***NOT ***vary with distance

Answer 66

* Create a simple circuit

Answer 67

* Symbol=zig-zag line * There is ***ALWAYS*** a ***voltage drop*** across a resistor when current flows through it * Internal Resistance * batteries experience internal resistance dur to the (inherent) *resistivity of their internal components* * This results in a voltage drop, and therefore ***DECREASES ***(slightly) ***THE TERMINAL VOLTAGE OF THE BATTERY*** * Current flow through parallel resistors is always *inversely proportional *to ***resistance*** * if one resistor has 2X the resistance, it will receive ½ the current

Answer 68

* F_m= mg/ (# of vertical ropes ***_directly_ lifting*** the mass) ***CAUTION: *** * Not ***_every_*** rope that is vertically oriented should be counted and entered into the above equation * To be counted, a vertical section of rope must life the mass ***directly*** * ******either by being attached ***TO*** the mass, or * ***by lifting a _pulley_*** that is attached to the mass * To test, imagine grabbing ***ONLY THAT ROPE*** and pulling it upward. Would the mass lift?

Answer 69

* ***All*** *of these waves are* ***LIGHT!*** * Longer wavelength * **lower** frequency * ***LESS ENERGY*** * Shorter wavelength * **higher** frequency * ***MORE ENERGY***

Answer 70

* ***AS PHYSICAL PACKETS OF LIGHT! *** * ******Visualize one of these packages striking a flat boundary at an angle. * It is easy to visualize that one corner of our little “light packet” is going to hit the surface first—before the other corner does. * If the light is passing from a low index medium to a high index medium, that first corner is suddenly going to be forced to go slower than any other part of the packet that is still in the less dense medium, much like what happens when a car tire goes off the road and hits a soft shoulder. * The “light packet” will tend to ***pivot around the corner that is “stuck” in the higher-index medium.*** * We can intuit exactly which way the light will bend.

Answer 71

* PE_elastic= ½kx²

Answer 72

* Converging (aka convex, positive) * ***_USUALLY (!!)_*** produces a ***positive, real, inverted image*** * When "p" is inside the focal point, it produces a ***negative, virtual, upright image*** * Diverging (aka concave, negative) * ***ALWAYS (!!)*** produces a ***negative, virtual, upright image*** * Far away objects * assume the light hitting the lens ***are all PARALLEL*** * As object approaches the lens, the image will ***no longer*** be exactly at the focal point *f*

Answer 73

* The capacity to do ***WORK***

Answer 74

* F_necessary= mg * Solving for force needed *without* a machine helps when comparing it to force needed *with* a machine * Factors will differ by an exact ***ratio*** (e.g. 1:5)

Answer 75

* PE_capacitor= ½ QV * PE_capacitor= ½ CV² * PE_capacitor=½Q²/C

Answer 76

* Symbol: two vertical lines of UNequal length * Longer line= (+) terminal * shorter line= (-) terminal * Batteries=***electron "pumps" that push electrons _onto the negative terminal_ of the battery*** * this creates a *separation of charge*, and therefore a ***potential difference*** b/t terminals * this drives electron flow *around the circuit t*o the positive terminal * All batteries cause ***A SEPARATION OF CHARGE*** * (which in turn creates a voltage)

Answer 77

* The “root mean square” (RMS) method of calculating both voltage and current are necessary for alternating current applications because the current and voltage over time are sinusoidal. * This creates a ***problem ,*** because the average of a sine wave centered _at the origin_ is ***zero***. * If you randomly sampled the voltage in your household wiring it could literally have a voltage of 120V *one* instant and a voltage of -120V the *next* instant. * That would ***average*** to zero, even though the alternating current does deliver a continuously useful source of power (It can dissipate energy during both cycles). * Power companies therefore use the RMS method to calculate the ***average power*** ***delivered to your home*** * RMS is just a mathematical calculation and it can be applied to voltage, current, to sine waves, or even to other waveforms such as square waves. * To find RMS, you take readings at various time intervals, ***square*** all of those readings, take the ***average of those squares*** (i.e., the mean of the squares) and then take the ***square root of that average***.

Answer 78

1. Alternating Current (AC) * Both the polarity of the voltage and the direction of the current ***periodically reverse.*** * A graph of current versus time for an AC current creates a sine wave 2. Direct Current (DC) * Direct flow of current through a circuit from positive to negative * (or in terms of electron flow, from negative to positive). * DC current is the kind of power used in automobiles because it comes directly from the battery. * In fact, if something uses a battery you would be perfectly safe on the MCAT to assume that ***it must be an example of DC current.***

Answer 79

* F=qvBsinθ * θ=angle between v and B * Units (of B): * N\*s/C\*m OR * Kg/A\*s²

Answer 80

* **P=IV** * Just memorize this one * Solve V=IR for the missing variable, then plug it in to get the other two

Answer 81

* **Intensity (dB)= 10\* log ( I / I₀)** * I=intensity of the sound wave in (W/m²) * I₀= threshold of human hearing * I₀=1 x 10^-12 W/m² * will always be given

Answer 82

*_The energy of:_* * the **internal vibrations*** * and **random motions of molecules** and/or atoms* * within a system* * Non-conservative forces (such as **friction** or **drag**) acting on a moving object results in the _transfer_ of: ***KE⇒ INTERNAL ENERGY***

Answer 83

* The system we have outlined simplifies everything into **up/down** or **left/right** forces. * You may well have a force that acts in two-dimensions, say at an angle of 30° to the horizontal. * In such cases simply enter into your table the ***formula that predicts the component of that force*** that acts up, down, left or right.

Answer 84

* ***ME=KE+PE*** * ******In the absence of no-conservative forces, Mechanical Energy is ***CONSERVED*** * ******aka "Total Energy" is conserved

Answer 85

* Wave speed is typically equal to *the **square root** of an **ELASTIC** property* of the medium divided *by an **INTERTIAL** property* * ***v =*** *√****(elastic/inertial) *** * The elastic property is often called a ***“modulus”.*** * The inertial property is a ***type of density. ***

Answer 86

1. Terminal velocity (Fair=mg) 2. constant velocity 3. Objects at rest 4. Balanced fulcrums * or boards hanging from strings 5. Objects floating in a liquid

Answer 87

* Index of Refraction * **n=c/v** * Snell's Law * **n₁sinθ₁=n₂sinθ₂**

Answer 88

* all forces acting down the plane are “**down** forces” * all forces acting up the plane “**up** forces.” * The force down the plane due to gravity is always **F = mgsinθ**. * The force of friction is always **parallel** to the plane **opposite** the direction of motion. * There will ***_NEVER_*** be **acceleration** perpendicular to the plane * so you can **ignore these forces**.

Answer 89

* PE_elec= Kqq/r * PE_elec= qEd * PE_elec= qV

Answer 90

* ***EQUAL DISTANCES*** on either side of the mirror

Answer 91

* The elastic property is called the “bulk modulus” **(B)** * ***directly proportional*** to ***BOTH *** * ******density _and_ * temperature * ∴ for gases, the velocity ends up having this "temperature dependence:" * **v ~ √(T)** * The inertial property is normal density, ρ * **v = √(B/ρ)**

Answer 92

* Negative (-) Charge=***electrons*** * Positive (+) Charge= relatively ***FEWER*** electrons

Answer 93

* For light crossing a boundary from a slower to a faster medium (like from glass or water into air), if the angle of refraction would be 90° or more, the incident light ***does not enter the second medium at all!!*** * ******100% of the light is reflected off the boundary and ***back into the first medium***. * For total internal reflection to occur, the light must be passing from a **higher index** medium to a **lower index** medium. * Formula * n₁sinθ₁=n₂sin_90º_ ***SO...*** * **sinθ₁=n₂/n₁**

Answer 94

Transverse mechanical waves require a fairly **STIFF MEDIUM** in order to propagate * ∴ cannot propagate in **liquids** or **gases** ex: **strings** on a musical instrument

Answer 95

**_Batteries in parallel:_** **TOTAL** voltage= the **HIGHEST** voltage of **any** one of the batteries in parallel

Answer 96

**CURRENT** FLOW goes from **(+)⇒(-)** **ELECTRON** FLOW is the opposite **(-)⇒(+)**

Answer 97

*When one object is vibrating near another object it can cause the neighboring object* ***to begin vibrating at that SAME frequency*** If the **exact** frequency at which the second object is caused to vibrate **happens** to be one of its "natural frequencies" (i.e., **harmonics**): _the two objects are said to be "**in resonance"**_ * ...and via **CONSTRUCTIVE** **interference** can produce a much **LOUDER** sound! If the first object causes a vibration in the second object that is **NOT** a match to one of its natural frequencies, resonance does **NOT** occur

Answer 98

Changing **TEMPERATURE** is the **ONLY WAY** you can change resistance in a circuit!

Answer 99

**Δf/f_s = v/c** **Δλ/λ_s = v/c** The answer is of the equation is **CHANGE IN λ** * which is often **NOT** what they're asking for!! ***This** value must be* ***added** or **subtracted** from the **initial** value* * in order to get the **ACTUAL** value* * due to the **doppler** effect* _If the relative motion is **TOWARDS** each other:_ * Add to the **FREQUENCY** * (subtract from the λ) _If the relative motion is **AWAY FROM** each other:_ * Add to the **λ** * (subtract from the frequency)

Answer 100

***1.0 x 10⁶C*** **4E^-13 - 2.4E^-13=1.6E^-13** *Divide by **1.6E^-19** to get 1**E⁶C*** This question requires that you remember **the charge on an electron is -1.6 x 10^-19C** * Subtract the **final** charge from the **initial** charge and **divide** **by the charge on one electron** * to get 1.0 x 10⁶C Remember that electron charge is **quantized** according to -1.6 x 10^-19C * In other words, you cannot have a **fraction** or **decimal** of an electron * In practice, the charge of an electron is so small that generally it is not possible to count individual electrons with precision *

Answer 101

**25V** ## Footnote ***E=F/q** **OR** **E=V/d*** _To answer this question you must remember that the **strength of a field** (**"E"**) is defined by:_ * the **force** it can exert on a given **charge**, * expressed in: * **Newtons /Coulomb** or * **Volts /meter** * *(Why? Remember that **V = Ed**, solve for E)* **Calculate E** using **N/C** * set that number **equal to V/m** * then **solve for V**

Answer 102

**n\*fundamental frequency** ## Footnote "Fundamental Frequency"= **FIRST** harmonic object resonates at (e.g., if the first harmonic is exactly 200 Hz, the 2nd is 400 Hz, the 3rd is 600 Hz, etc.)

Answer 103

* The **first** harmonic is called * the **fundamental frequency**, * the **second** harmonic is called * the **1st overtone** * the **third** harmonic is called * the **2nd overtone**, and so forth