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Physics > ch 6 - circuits > Flashcards

ch 6 - circuits Flashcards

1
Q

current

A

considered the flow of positive charge even though only negative charges are actually moving

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2
Q

metallic conductivity

A

solid metals and molten forms of some salts

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3
Q

electrolytic conductivity

A

seen in solutions

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4
Q

conductance

A

reciprocal of resistance, property we will examine in detail later

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5
Q

SI unit for conductance

A

siemens (S) sometimes given as siemens per meter (S/m) for conductivity

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6
Q

metallic bond

A

an equal distribution of charge density of free electrons across all of the neutral atoms within the metallic mass

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7
Q

how to measure conductivity of electrolyte solution

A

place solution as a resistor in a circuit and measure changes in voltage across the solution

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8
Q

electrical current

A

the flow of charge between two points at different electrical potentials connected by a conductor (such as copper wire)

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9
Q

magnitude of current

A

I(i) = Q/change in t; amount of charge Q passing through the conductor per unit time

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10
Q

SI unit of current

A

ampere (1 A = 1 C/s)

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11
Q

how would positive charge flow if it flowed (direction of current)

A

from higher electrical potential to lower potential

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12
Q

direct current

A

tested to exclusion of alternating current (AC) on mcat; charge flows in one direction only

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13
Q

potential difference (voltage)

A

produced by electric generator, galvanic (voltaic) cell, a group of cells wired into a battery, etc.

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14
Q

electromotive force (emf or epsilon)

A

when no charge is moving between the two terminals of a cell that are at different potential values; not actually a force but is a potential difference measured in joules per coulomb (1 V = 1 J/C)

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15
Q

Kirchhoff’s junction rule

A

at any point or junction in a circuit, the sum of currents directed into that point equals the sum of currents directed away from that point; expressed as I (sub into junction) = I (sub leaving junction)

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16
Q

Kirchhoff’s loop rule

A

around any closed circuit loop, the sum of voltage sources will always be equal to the sum of voltage (potential) drops; V (sub source) = V (sub drop)
true of closed loops and not necessarily entire circuits

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17
Q

Resistance

A

opposition within any material to the movement and flow of charge; insulators have very high resistance; conductors have very low resistance

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18
Q

resistors

A

conductive materials that offer amounts of resistance between that provided by conductors and insulators; dependent on characteristics of it like resistivity, length, cross-sectional area, and temp.

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19
Q

equation for resistance

A

R = (fancy p x L)/A fancy p = resistivity, L = length of the resister, A = cross-sectional area

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20
Q

resistivity

A

intrinsic resistance to current flow in a material represented by fancy p; SI unit is ohm-meter (omega x m)

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21
Q

Length of resistor

A

resistance is directly proportional to length of resistor; longer means electrons will have to travel greater distance through a resistant material; if resistor doubles in length, resistance will also double

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22
Q

Cross-sectional area of resistors

A

inverse proportionality to resistance; if cross-sectional area is doubled, resistance is cut in half increasing number of conduction pathways

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23
Q

Temperature of resistors

A

most conductors have greater resistance at higher temps due to increased thermal oscillation of the atoms in the conductive material which produces greater resistance to electron flow

24
Q

Ohm’s Law

A

states that for a given magnitude of resistance, the voltage drop across the resistor will be proportional to the magnitude of the current. And for a given resistance, the magnitude of the current will be proportional to the magnitude of the emf (voltage) impressed upon the circuit. V = IR where V = voltage drop, I is the current and R is the magnitude of the resistance measured in ohms (omega symbol)

25
Q

actual voltage supplied by a cell to a circuit due to internal resistance

A

it is less: V = E sub cell - ir sub int where V is the voltage provided by the cell, E sub cell is the emf of the cell, i is the current through the cell and r sub int is its internal resistance

26
Q

internal resistance

A

there is a measure of internal resistance by every conductor; if the cell is not actually driving any current the internal resistance is 0 and voltage of cell is = to emf. If not zero, then voltage is less than emf

27
Q

secondary batteries

A

certain type of power cells that can be recharged by an external voltage applied in such a way to drive current toward the positive end of the secondary battery rather than the typical of moving from the positive (higher potential) end to the negative (lower potential) end; acts as galvanic cell when discharging and electrolytic cell when recharging

28
Q

Power equation

A

ratio of work (energy expenditure) to time: P = W/t = delta E/t

29
Q

equation for rate at which energy is dissipated by a resistor

A

= the power of a resistor: P = IV = I^2R = V^2/R; I = current through resistor; V = voltage drop across resistor; R = resistance of resistor

30
Q

series

A

one of two ways in which resistors can be connected into a circuit, all current must pass sequentially through each resistor connected in a linear arrangement

31
Q

parallel

A

one of two ways in which resistors can be connected into a circuit, current will divide to pass through resistors separately

32
Q

total voltage drop for series of resistors

A

V sub S = V sub 1 + V sub 2 + … + V sub n

33
Q

resistances of resistors in series

A

R sub S = R sub 1 + R sub 2 + …. + R sub n

34
Q

equivalent or resultant resistance

A

set of resistors wired in series can be treated as a single resistor with a resistance equal to the sum of the individual resistances

35
Q

voltage in circuits with parallel arrangements of resistors

A

V sub P = V sub 1 = V sub 2 … = V sub n because all lines originate at a common high potential terminal and move to common low potential terminal

36
Q

equivalent resistance of resistors in parallel

A

1/R sub p = 1/R sub 1 + 1/R sub 2 + 1/R sub 3 + … + 1/R sub n; total will always decrease as more resistors are added

37
Q

when some number (n) of identical resistors are wired in parallel what is total resistance?

A

R/n note: (I (current) sub total)/n is also true for this

38
Q

Four physical quantities that determine resistance of a resistor

A

cross-sectional area, resistivity, length, temp

39
Q

Capacitors

A

characterized by their ability to hold charge at a particular voltage; ex defibrillator

40
Q

capacitance

A

the ratio of the magnitude of the charge stored on one plate to the potential difference (voltage) across the capacitor; If voltage is applied across the plates of a capacitor and a charge (Q) collects on it (+Q at positive end and -Q at negative plate), then capacitance = C = Q/V

41
Q

SI unit for capacitance

A

farad (1 F = 1 C/V) also given in microfarads (1 fancy uF = 1 x 10^-6 F) or picofarads (1 pF = 1 x 10^-12 F)

42
Q

Do not confuse the farad with faraday constant:

A

faraday constant is amount of charge in one mole of electrons (96,485 C/mol e-)

43
Q

parallel plate capacitance

A

C = epsilon sub 0 (A/d); epsilon sub 0 = permittivity of free space (8.85 x 10^-12 F/m); A = area of overlap of the two plates; d = distance of separation of the two plates

44
Q

uniform electric field

A

set up by the separation of charges between plates with parallel field vectors in capacitors: E = V/d

45
Q

potential energy stored in a capacitor

A

U = 1/2 x CV^2

46
Q

dielectric materials

A

insulation

47
Q

dielectric constant (fancy K)

A

this is the factor by which an added insulator increases capacitance when introduced between the plates of a capacitor; arises from a decrease in voltage and increase in stored charge

48
Q

equation for capacitance due to dielectric material

A

C’ = fancy K x C; C’ = new capacitance with the dielectric present; C = original capacitance; fancy K = dielectric constant

49
Q

What happens to total capacitance in series if more capacitors are added

A

it decreases (resistance increases)

50
Q

equation for calculating equivalent capacitance for capacitors in series

A

1/C sub S = 1/C sub 1 + 1/C sub 2 + 1/C sub 3 + … + 1/C sub n

51
Q

what happens to capacitance when capacitors are added in parallel

A

capacitance increases (resistance decreases)

52
Q

ammeters

A

used to measure the current at some point within a circuit

53
Q

voltmeters

A

requires circuit to be active; also use magnetic properties of current-carrying wires; used to measure voltage drop across two points in a circuit

54
Q

ohmmeters

A

used like ammeters but with a circuit that is not active. Measures resistance through calculation using Ohm’s Law

55
Q

equation for current

A

I = Q/change in time

Physics (9 decks)

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