Flashcards in ch 6 - circuits Deck (55)

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1

## current

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

2

## metallic conductivity

### solid metals and molten forms of some salts

3

## electrolytic conductivity

### seen in solutions

4

## conductance

### reciprocal of resistance, property we will examine in detail later

5

## SI unit for conductance

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

6

## metallic bond

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

7

## how to measure conductivity of electrolyte solution

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

8

## electrical current

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

9

## magnitude of current

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

10

## SI unit of current

### ampere (1 A = 1 C/s)

11

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

### from higher electrical potential to lower potential

12

## direct current

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

13

## potential difference (voltage)

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

14

## electromotive force (emf or epsilon)

### 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)

15

## Kirchhoff's junction rule

### 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)

16

## Kirchhoff's loop rule

###
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

17

## Resistance

### 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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## resistors

### 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.

19

## equation for resistance

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

20

## resistivity

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

21

## Length of resistor

### 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

22

## Cross-sectional area of resistors

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

23

## Temperature of resistors

### 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

## Ohm's Law

### 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

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

### 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

## internal resistance

### 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

## secondary batteries

### 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

## Power equation

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

29

## equation for rate at which energy is dissipated by a resistor

### = 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

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