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MCAT physics > chapter 7 > Flashcards

chapter 7 Flashcards

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1
Q

When charge flows through a conductor in a specific direction, that movement of charge is known as?

A
  • current (positive so the direction in which current flows is opposite of the actual flow of electrons)
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2
Q

Current (I) is defined as?

A
  • the amount of charge that flows through a location over an interval of time
    • current equals charge divided by time and the SI unit is the ampere (A)
      • 1A = 1C/1s
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3
Q

why does current move through a conductor?

A
  • the motion of current in circuits is driven by voltage differentials (electromotive force emf)
    • current flows from a positive point of voltage to a relatively negative point of voltage
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4
Q

voltage equals current times resistance which is known as?

A
  • ohm’s law
    • V = IR
      • R has units of ohms and 1 ohm = 1 volt divided by 1 ampere
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5
Q

power = VI

A
  • Utilizing ohm’s law to idnetify ways of rewriting the quantities of voltage and current in terms of resistance, we can derive the following sets of equivalent equations for the power disspiated by a resistor
    • P = IV = I2R = V2/R
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6
Q

what is Kirchhoff’s first law?

A
  • applies to currents and states that for anu junction in a circuit, the sum of current entering the junction must equal the sum of the current exiting the junction
    • at a junction: Iin = Iout
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7
Q

what is Kirchhoff’s second law?

A
  • applies to voltage and states that for a closed circuit, the sum of the voltage drops throught the circuit is equal to the source voltage (emf) of the circuit as a qhole
    • over a closed circuit: Vsource = sumVcircuit
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8
Q

resistors added in series are added one after another such that an uninterrupted flow of current goes first through one resistor, then another, and so on.

in contrast, resistors added in parallel involve the current being split, such that one branch of the current goes through one resistor and one branch of current goes through another:

A
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9
Q

for a circuit with resistoris R1, R2,… Rn wired in series:

A
  • Itotal = I1 = I2 = … In
  • Vsource = V1 + V2 + … Vn
  • Rtotal = R1 + R2 + … Rn
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10
Q

for resistors added in parallel:

A
  • Itotal = I1 = I2 = … In
  • Vsource = V1 + V2 + … Vn
  • 1/Rtotal = 1/R1 + 1/R2 + … 1/Rn
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11
Q

current is measured using?

A
  • ammeters
    • an ammeter is inserted in series into a circuit and is able to ‘capture’ the entire flow of the curreny based on the magnetic field induced by the current moving through a wire
      • should have zero resistance
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12
Q

what is a voltmeter?

A
  • connected to a resistor in parallel and it has a known resistance and siphons off some current which is measured to calculate voltage based on Ohm’s law (V = IR)
    • should have high resistance and low current
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13
Q

what is an Ohmmeter?

A
  • used to measure resistance
    • a known voltage is supplied across a resistor and the resulting current is measured or a constant and known current is applied across a resistor and the voltage drop is measured
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14
Q

what is a capacitor?

A
  • a device containing two physically separated components in which opposite charges are accumulated
    • idealized capacitors consist of 2 parallel, conductive plates separated by a non-conductive, insulating material that is known as a dielectric material
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15
Q

the accumulation of charge in a capacitor is caused by?

A
  • the application of a voltage. and the degree to which a capacitor can store charge is defined as its capacitance
    • Q = VC
      • capacitance is defined as the amount of charge stored in a capacitor for a given voltage
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16
Q

what are the 2 ways to increase the charge in a capacitor?

A
  • increase the voltage
  • increase the capacitance
17
Q

The capacitance is given by the following equation: (in a vacuum)

A
  • C = e0 = A/d
    • e0 is a constant known as the permittivity of free space (8.85 x 10-12 F/m)
    • A is the overlapping cross-sectional area of the platees
    • d is the distance between them
      • increasing the area of the platers and bringing them closer together will increase the capacitance
18
Q

In order to streamline comparisons of the dielectric properties of various substances to that of a vacuum, we define the dielectric constant (k) of a substance as the ratio of its permittivity (e) to e0:

A
  • k = e/e0
    • the greater the dielectric constant, the more charge a capacitor can store at a given voltage
19
Q

In a unitiform electric field, there is an equation that states that the strength of an electric field is equal to the voltage difference divided by the distance between the plates:

A
  • E = v/d
    • E = F/q applies to electric fields in general
20
Q

Capacitors have the function of storing energy in the form of the electric field that they generate. this is a form of potential energy and can be expressed using this equation:

A
  • PE = 1/2 CV2
21
Q

capacitors can be added in series or in parallel:

A
  • series = 1/Ctotal = 1/C1 + 1/C2 + … 1/Cn
  • parallel = = Ctotal = C1 + C2 + … Cn
22
Q

What are magnetic fields?

A
  • act on charges (moving charges)
    • the unit of strength of magnetic fields in teh tesla (T) and is defined as the magnitude of a magentic field through which a particle with a charge of 1C moving perpendicularly to the field at 1 m/s experiences a force of 1N, OR 1 T = N•s/C•m (large unit)
23
Q

what are the 2 main ways to generate a magnetic field?

A
  • by magnetic materials and by moving charges
24
Q

Materials with paired electrons do not generate a magnetic field and cannot become magentized. they are known as?

A
  • diamagnetic
25
Q

If a material has unpaired electrons with random spins, it means that the material as a whole has no net magnetic dipole on its own. these materials are known as?

A
  • paramagentic
    • can be magnetically polarized by an external field
26
Q

materials with unpaired electrons in which the spin of the electrons can be permanently affected by the application of an external magnetic fiels is known as?

A
  • ferromagnetic
27
Q

magnets have both a north and south pole:

A
  • north and south are attracted, while north/north and south/south exhibit repulsion
28
Q

the strength of the field is given by this equation:

A
  • B = uoI/2Πr
    • u0 is the permability of free space
    • I is the current running through the wire
    • r is the distance from the wire
      • B is directly proportional to current and inversely but linearly proportional to r
29
Q

the magnetic field around a current-carrying wire has field lines that run in concentric circles, and the directionality of such magnetic fields is determined by one of the 2 right hand rules:

A
  • to determine the direction of the magnetic field at a point around a current-carrying wire, simply allign your right thumb with the direction of the current flow, and your fingers will curve around in the direction of the field
30
Q

Magnetic fields act on moving charges. In particular, the force exerted by a magnetic field on a moving particle with velocity v and charge q is given by the following:

A
  • Fb = qvB(sin theta)
31
Q

how to apply the second right hand rule:

A
  • used to determine the effects of a magentic field on a moving particke
    • your thumb is used to indicate the direction in which the charge is moving
    • your fingers are used to indicate the direction of the magnetic field
    • the resulting force either points up or down from your palm
      • if it points up, it is postive
      • if it points down from the back of your hand, it is negative
32
Q

within a uniform electric field, a particle will experience?

A
  • circular motion
    • m(v2/r) = qvB
33
Q

equation to obtain the force exerted on a current-carrying wire?

A

FB = I L B sin theta

  • B is the strength of the magnetic force
  • current is I
  • L is length
34
Q

what is ‘Lorentz force’?

A
  • refers to the cumulative force exerted on a charged particle by an electric field and a magnetic field because these fields co-occur
    • Ftotal = Felectric + Fmagnetic
      • Ftotal = qE + qvB(sin theta)

MCAT physics (12 decks)

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