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B MCAT > B MCAT- Physics > Flashcards

B MCAT- Physics Flashcards

1
Q

mechanical advantage is the ratio of …

A

input force/output force.

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2
Q

efficiency is the ratio of …

A

useful work / total work performed by a system.

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3
Q

W=f d

A
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4
Q

V=change in position / change in time

A
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5
Q

g=

A

9.81 m/s^2

For MCAT, can round to 10 m/s^2.

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6
Q

W=mg

A
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7
Q

F=ma

A
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8
Q

U initial + K initial = K final + U final

A
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9
Q

Central dogma of energy in B’s words

A

Energy is the ability to do work.
Energy is conserved.
Work converts potential energy to kinetic energy (or elastic potential energy) and visa versa.

Potential energy is always = force x distance. This often comes in the form of U=mgh.

Kinetic energy is 1/2mv^2. So velocity has a much greater impact on KE than mass does.

Many problems are just asking for the delta, so remember to simplify and set the zero point where ever is most convenient.

In many frictionless ramp questions, the angles have no impact on final velocity. E.g. Given two boxes of same weight sliding off a truck down ramps of 15 vs. 45 degrees, they end with the same velocity.

Often the trig can be approximated.

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10
Q

Pressure vs. Force

A

Pressure is Force/Area.

ex. squeeze a water bottle and the “diver” goes down.

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11
Q

Buoyant Force

A

Buoyant force is the difference between the force on the top vs. bottom of an object in liquid.

BF acting on an object is equal to the density of the liquid it is in multiplied by the amount of fluid displaced by the object.

Buoyant force is equal to the weight of the fluid the object displaces. (Archimedes Principle)

Buoyant force is equal and opposite to the force of gravity on a floating object. And F=mg.

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12
Q

Specific Gravity/ Relative Density

A

The ratio of densities between an object/substance and a reference fluid.

sg=p object/p reference fluid

kg/L

Specific gravity, also called relative density, is the ratio of the density of a substance to that of a standard substance, usually water at 1.0 kg per litre (62.4 pounds per cubic foot).

Gases are commonly compared with dry air, which has a density of 1.29 grams per litre (1.29 ounces per cubic foot) under so-called standard conditions (0 °C and a pressure of 1 standard atmosphere).

If an object has a lower specific gravity than a given fluid or gas = the object will float in that fluid or gas.

Specific Gravity will also tell us what portion of object will be displaced in the fluid while it floats. Objects more dense than the fluid will have ratio > 1 and will sink.

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13
Q

ideal gas = theoretical = no volume = no intermolecular forces = no loss of energy from collisions (elastic collisions)

A
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14
Q

Relationship between pressure and volume

A

smaller volume = more pressure = more frequent collisions

Boyle’s Law:
PV=Constant, so
P and V inversely proportional

Increasing the temperature will make particles more faster. So, if you take a container and keep the number of particles and the pressure constant, then increasing the temperature will increase the volume of the container.

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15
Q

Relationship between volume and temperature

A

Charles’ Law:
V/T=Constant
So, V and T inversely proportional.
Decrease in V=Constant x increase in T.

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16
Q

Definition of temperature in Kelvin

A

Temperature is the average kinetic energy of all the molecules in a system.

At zero Kelvin–absolute zero–all particles has stopped moving (theoretical).

Absolute zero Kelvin = -273 degrees C

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17
Q

Moles and Volume

A

Avogadro’s Law:
Vol/number of moles = constant

increase in vol = constant x increase in number of moles.
Ex. Moles of gas can decrease with temperature changing to liquid.

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18
Q

Ideal Gas Law

A

PV=nRT

Pressure x Volume = number of moles x ideal gas constant x temperature
Value of R depends on units used.

UNITS!!!!!

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19
Q

STP for gas problems

A

standard temperature and pressure for gas law problems:
= 273 Kelvin (0 degrees Celsius)
1 atm
Vol of 1 mole of an ideal gas is 22.4 L

standard conditions for thermodynamics problems:
= 298 Kelvin (25 degrees Celsius)

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20
Q

Pascal’s Law, pressure and fluid

A

pressure exerted on an incompressible fluid is the same throughout the fluid. F/A is the same throughout.

So, if area is smaller in one spot, it increases the force proportional to the area. Ex. Hydraulic lifts

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21
Q

density = mass/ volume

A

kg
L
1000 L = 1 meter^3

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22
Q

Convert Celsius to Kelvin

A

degrees Celsius + 273 = Kelvin

Water boils at:
373 Kelvin
100 degrees Celsius
212 degrees F

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23
Q

Henry’s Law

A

The amount of gas dissolved in a liquid is proportional to the partial pressure of the gas above the liquid.

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24
Q

relationship between pressure and force

A

Pressure (in pascals) =
Force (in newtons) /Area (in m^2)

P=F/A

This is how hydraulic lifts work.

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25
Q

Under what conditions is an ideal gas LEAST likely to behave like an ideal gas?

A

High pressure, and low temperature.

High pressure, small volume, low temp conditions mean that gases don’t have as much space to disperse and overcome intermolecular forces.

Consider Ideal Gas Law:
PV=nRT

26
Q

Speed of sound through different medium

A

velocity of sound = square root of the ratio of the bulk modulus / density of the medium.

The bulk modulus is measure of a medium’s resistance to compression. Larger B = less compressible.

Therefore, sound travels fastest through solids like bone, slower through liquid, and the slowest through gas.

27
Q

heat capacity (mc)

A

The energy needed to raise the temperature of a system by 1 degree.

heat capacity = mass * specific heat
(mc)

Q=mcdeltaT

28
Q

specific heat (c)

A

Specific heat is the ability of something to hold heat–resistance to change of heat.

specific heat = heat capacity per unit mass
(c)
(i.e. mc/m)

e.g. Water has a high specific heat; it can hold heat well.
Air has a lower specific heat than water; it does not hold heat as well.

Q=mcdeltaT

29
Q

Latent heat (L)

A

Heat absorbed that does not change the temperature of the system.

i.e. delta H of a phase change

Q=mL

30
Q

How does pressure affect phase change?

A

The lower the ambient pressure, the easier it is to boil something.
i.e. There is less heat energy needed to change the system.

Water boils at a slightly lower temperature at lower pressure (higher elevations).

31
Q

Conduction

A

Exchange of kinetic energy between particles.
i.e. Heat energy transfer via particles bouncing off one another.

32
Q

Thermal conductivity (k)

A

The ability of something to conduct heat (to transfer energy between particles).

Metals have a large k. Metal can heat and cool very quickly.
Gases, non-metals have a small k.

33
Q

Convection

A

Energy transferred by movement of a fluid (liquid or gas).

e.g. A radiator (steam), air conditioner, convection oven

34
Q

Radiation

A

Conversion of thermal energy into electromagnetic waves.

Only form of energy transfer that can go through a vacuum. This is why the sun can heat the earth.

35
Q

bond enthalpy

A

the energy stored in a bond between two atoms

36
Q

calculating temperature change

A

Q = mcdeltaT

37
Q

Thermodynamic systems energy and work equation

A

delta E = Q - Wby

change in energy of the system (E) = heat added to the system (Q) minus work done BY the system (Wby)

Helpful to set up a table with Temp change, Work by </> 0, and delta E </> 0.

38
Q

Volume of gas at STP

A

22.4L

39
Q

Volume and buoyancy

A

Volume and buoyancy have a direct relationship. As volume increases, so does buoyancy, and visa versa.

40
Q

Ideal gas law R =

A

R = 0.082 (LATM)/(Kmol)

PV=nRT

41
Q

density of water

A

~1000 kg/m^3

42
Q

relationship between velocity and area

A

velocity and area are inversely proportional.
v1A1=v2A2

Remember that A of a circle = pi*r^2

43
Q

light energy…
C=
energy of a photon=

A

C = speed of light = 3*10^8
C=(freq)(wavelength)

Energy of a photon E = hf = (h*c)/wavelength

h=6.6*10^-34 Js

44
Q

magnification formula for mirrors and lenses

A

m = (image distance)/(object distance)

|m|>1= magnified
|m|<1= minimized

negative (-) m indicates real image, inverted.
positive (+) m indicates virtual image, upright.

45
Q

Hyperopia

A

Hyperopia is far-sightedness.

Eyeball too SHORT for radius of curvature, so image forms BEHIND RETINA.

Need a converging (convex) lens. Always create a virtual image at the ideal focal point.

Power (in diaptors) is positive +.

Use 1/f=1/do + 1/di
P=1/f

46
Q

Myopia

A

Myopia is near-sightedness.

Eyeball is too LONG for radius of curvature. Image forms inside retina. do is infinite, so f~di.

Need a diverging (concave) lens.

Power (in diaptors) is negative - .

My lasik corrected my myopia by making my radius of curvature bend light less.

47
Q

2 types of electrochemical cells:
Galvanic cells…
Electrolytic cells…

A

Galvanic/voltaic cells RELEASE ENERGY.
(Assume that a battery is a galvanic cell unless otherwise stated or reference to charging.) Directs the movement of electrons from a redox reaction to a wire making an electromotive force / current of electrons flowing from the anode to the cathode. The salt bridge (or in earlier battery models a porous divider) provides a means for charged particles to flow again and neutralize the solutions so that the reaction and current can continue.

Electrolytic cells STORE ENERGY. Two inert electrodes in solution. Electrons flow from an external power source toward one electrode, making it the cathode, where reduction happens. Then the anions flow to the other electrode where they are oxidized, making that the anode.

Electrochemical half reactions draw out the flow of electrons, often with reduction potential. The reduction potential of each half reaction indicates the electromotive force (related to voltage) of each half reaction. The rxn with the larger magnitude reduction potential will be the one that gets the electrons (the reduction rxn that happens at the cathode). The oxidation rxn will happen at the anode.

48
Q

turbulent vs. laminar flow

A

Turbulent flow is rough and disorderly. Can form EDDIES–swirls of fluid on the downstream side of an obstacle.

Laminar flow is smooth and orderly. Modeled as STREAMLINES–layers of flow, sometimes moving faster near the sides of a pipe than in the middle.

49
Q

Ideal fluid

A

An ideal fluid is one that has low viscosity (resistance to flow). Gases generally have lower viscosity than liquids.

50
Q

range of frequency that a human can hear

A

20 - 20,000 Hz

Ultrasound, xrays, etc. are all above this range.

The wavelength and velocity of a wave changes as it moves through different mediums, but the frequency remains the same. E=hf

51
Q

conservation of energy equations

A

conservation of energy can be used to solve all sorts of problems.
kinetic energy = 1/2 mv^2
potential energy = mgh

Related, power is change in energy over time. So, you can solve some problems subtracting initial KE or PE from final KE or PE and equating to power.

52
Q

Ecell

A

The electromotive force of a battery cell; the cell potential. Measured in voltage; positive reduction potential if spontaneous, negative reduction potential if nonspontaneous.

The magnitude of Ecell describes the amount of voltage produced by a spontaneous reaction (positive Ecell), or consumed by a nonspontaneous reaction (negative Ecell).

Discharging a battery = spontaneous; creates a positive Ecell to power something else.

deltaG=-nFEcell
where n is the number of electrons transferred, and F is Faraday’s constant. Negative because delta G and E cell will always have opposite signs. (neg delta G = spontaneous, pos Ecell = spontanteous)

A Voltmeter will tell you the Ecell value for a galvanic cell.

53
Q

In a cell, the anode is always the site of ___

A

The anode is always the site of oxidation.

54
Q

In a cell, the cathode is always the site of _____

A

The cathode is always the site of reduction.

55
Q

circuit strategy

A

V=iR
Resistance is measured in ohms.

The big battery line is the + side, small line is -. By convention, circuit problems use the flow of positive charge instead of electrons.

Resisters in PARALLEL divide the current, resulting in a net DECREASE IN RESISTANCE (smaller than any individual resister in the measurement). 1/Rt=1/R+1/R+1/R etc.
Total voltage of the circuit is fixed and resistance decreases, so current increases (i.e. more current pulled from battery).

Resister in SERIES INCREASE THE TOTAL RESISTANCE because current must pass through both/all in series (the total will be larger than any one resister in the series. Rt=R+R+R etc.
Total voltage of the system is fixed and resistance increases, so current decreases.

To calculate, start with the resisters in parallel, then move on to the resisters in series.

56
Q

capacitance

A

A parallel place capacitors involves two plates that store charge connected to a voltage source. + charge builds up on one plate, - charge builds up on the other, so potential energy is stored via the electric field between them. The magnitude of the electric field is larger with greater voltage (V), and E is larger with a smaller distance (d) between the plates. Note that the area of the plates doesn’t matter, because we assume the plates are much greater in size than the distance between them.
E=V/d

C=Q/V

Capacitance is measured in Farads. 1 F = 1 Coulumb per Volt.

While capacitor is charging, V is constant, and Q increases to maintain voltage. Once disconnected from the voltage source, Q is constant and V decreases.

Capacitors in series DECREASE the total capacitance (the sum of d increases).

Capacitors in parallel INCREASE the the total capacitance (total A increases).

57
Q

capacitance WITH a dielectric

A

A dielectric is an insulator (glass, plastic) that INCREASES capacitance when inserted between plates. Vacuum and air = 1.

The area of the plates matters, bigger area = bigger capacitance, since more space to store charge.

C=Q/V
(voltage constant while connected to the power source; dielectric increases C, Q goes up).

When inserting a dielectric/insulator, can use formula
C’=(dielectric constant)(C)

58
Q

Relating current, charge, time

A

change in current = change in charge/ change in time
i=q/t

59
Q

Relating charge and number or moles of electrons

A

Given moles of electrons, multiple:
Avagadro’s number (6 x 10^23)
by the moles of electrons
by the charge per electron (1.6 x 10^-19)

60
Q

Transformers

A

Power=current x voltage
P=iV

Power is constant at the transformer site.

A STEP-UP transformer increases voltage (thereby decreasing current).

A STEP-DOWN transformer decreases voltage (thereby increasing current).

61
Q

How do you know if a rxn took place in a galvanic vs. electrolytic cell?

A

If rxn is spontaneous (Positive Ecell, negative delta G) then it took place in a galvanic cell.

Opposite for electrolytic cells–nonspontaneous reactions.

62
Q

power, voltage, and resistance

A

Power=voltage^2 / resistance

B MCAT (11 decks)

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