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physics > ch 10 - resistance and resistivity > Flashcards

ch 10 - resistance and resistivity Flashcards

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1
Q

I-V characteristic

A

a graph of current against voltage for a particular component of an electrical circuit

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2
Q

resistance formula

A

R = V/I

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3
Q

resistance on an IV graph (if its straight line through origin)

A

reciprocal of gradient

CHECK AXIS IN CASE THEY ARE NOT SWITCHED

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4
Q

if connections to a resistor is switched

A

pd and current become opposite/negative

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5
Q

what is a resistor

A

an electical component whose resistance in a circuit remains constant, is independent of current or pd

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6
Q

Ohm’s law is obeyed when

A

current in a conductor is directly proportional to the pd across its ends

IV characteristic will show straight line through origin

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7
Q

ohmic component

A

a component that obeys Ohm’s laws

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8
Q

non ohmic component

A

a component that does not obey Ohm’s laws

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9
Q

filament lamp is (ohmic/non)

A

non ohmic

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10
Q

filament lamp graph

A

. line passes through origin
. roughly straight line for voltages close to zero
. curves towards x axis for very high and very low voltages, more resistance

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11
Q

thermistors are (ohmic/non)

A

non ohmic

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12
Q

thermistors

A

. made from metal oxides, eg. manganese and nickel

TYPES:–
. PTC - positive temperature coefficient (more T = more resistance) UNNEEDED

. NTC - negative temperature coefficient (more T = less resistance)

USES:–
. ice sensors on aircraft wings
. water temperature sensors in cars
. baby breathing monitors
. fire sensors
. overload protection in electric razor sockets

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13
Q

NTC thermistor

A

a device whose resistance decreases rapidly when the temperature increases

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14
Q

semiconductor diode is (ohmic/non)

A

non ohmic

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15
Q

diode

A

a component that allows current in one direction

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16
Q

diode details

A

. LED is a type, gives out light when it conducts
. graph : near 0 until positive V value (usually 6), when it shoots up

. when forward biased - conducts, fairly low resistance
. when reverse biased - tiny current, infinite resistance

. starts to conduct at threshold voltage
. used as rectifiers ( I in only one direction)

. AC to. DC

USUALLY
. made from silicon
. threshold V is 0.6

17
Q

diode details

A

. LED is a type, gives out light when it conducts
. graph : near 0 until positive V value (usually 6), when it shoots up

. when forward biased - conducts, fairly low resistance
. when reverse biased - tiny current, infinite resistance

. starts to conduct at threshold voltage
. used as rectifiers ( I in only one direction)

. AC to. DC

USUALLY
. made from silicon
. threshold V is 0.6

18
Q

threshold voltage

A

the minimum forward bias potential different across a LED when is starts to conduct and emit light

0.6

19
Q

when forward biased

A

conducts, fairly low resistance

20
Q

when reverse biased

A

tiny current, infinite resistance

21
Q

LEDs replacing filament lamps

A

. more costs for manufacture
. more energy efficient

22
Q

LDR

A

light dependent resistor

component whose resistance decreases when the light intensity increases

23
Q

LDR

A

. made of high resistance semiconductor
. if light falling is of high enough frequency, photons are absorbed by the semiconductor
. electrons thus releases
. better conduction
. resistance reduced

more light = less r

24
Q

factors affecting resistance

A

MORE
. temperature
. presence of impurities

MORE
resistance

25
Q

semiconductor conduction

A

more temperature = more conduction so less r

26
Q

in wire, r depends on

A

. length L
. cross sectional area A
. material wire is made from
. temperature of wire

27
Q

R formulas and proportionalities

A

R prop. to L
R prop. to 1/A
R prop. to L/A

R = pL / A

28
Q

what is resistivity

A

. a property of a material
. measure of its electrical resistance defined by p = RA/L
. units - ohm m

more temperature =
more resistivity =
more resistance

29
Q

double L in circuit is like

A

R plus R, R increases

30
Q

double A in a circuit is like

A

parallel, R decreases

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