Flashcards
Power and Resistivity
Flashcards do conjunto (26)
- 1Define powerRate of energy transfer / work done
- 2What are the 3 equations for power?P=IV
P=I^2 x R
P=V^2 / R - 3If voltage is increased by 3 times with a fixed resistance, then power increases by....9 times (as 3 x 3 = 9)
- 4What kind of property is resistivity?Intrinsic (doesn't change for a specific material)
- 5What factors does resistance depend on?Resistivity (p)
Length (L)
Cross-sectional area (A) - 6What is the equation for resistance of a material?R = pL / A
- 7What are the units for resistivity?Ωm
- 8Positive metal cations in lattice vibrate more as ....Temperature increases
- 9When temperature increases, it means that....Charge carriers (electrons) can't pass through as easily
- 10What else increases as temperature does?Resistance (this is called a positive temperature coefficient (PTC) )
- 11A thermistor is an example of a....Intrinsic semi-conductor
- 12When using a thermistor, as temperature increases, resistance.....Decreases
- 13Why does the resistance decrease?Number of charge carriers (electrons) increase with temperature
- 14Due to resistance decreasing with temperature, thermistors have a.....Negative temperature coefficient (NTC)
- 15Uses of thermistors:Temperature sensors
Resistance - temperature graphs - 16Resistance - temperature graph :
- 17Variation of resistance with temperature practical :Use: Ammeter, voltmeter , thermistor , beaker, Bunsen ,digital thermometer , power pack
Change temperature by heating water bath (or ice)
Get range of values from 0-50 degrees
Calculate resistance R=V/I
Temperature via thermometer
Plot R-T graph
Note: leave components in water for 1 min to allow for thermal equilibrium
Note: Stir water - 18Superconductivity means....Resistance = 0
- 19Resistance decreases with....Temperature
- 20A material can become superconductive at or below the....Critical temperature (Tc)
- 21Superconductivity on a graph:
- 22Superconductivity is used for....Creating a really strong electromagnetic field
To reduce power loss in cables - 23Using an LDR, as light intensity increases, resistance.....Decreases
- 24Resistance of an LDR decreases because....The number of charge carriers increase with light intensity (charge carriers = electrons)
- 25Uses of LDR's :Street lamps
Automatic headlights
(used as light sensors) - 26What is the equation of electrical energy?E=QV