3.5 - electricity Flashcards
What does the V-I graph look like for a fixed resistor? How does this differ for smaller/ bigger R?
Linear, going through the origin
smaller R has a steeper line/ bigger R has shallower line ON V-I GRAPH (opposite for I-V graph)
Includes negative
What does the V-I graph look like for a filament lamp?
curved graph which flattens out at origin, towards constant I, while V increases.
Includes negative
What does the V-I graph look like for a diode?
No negative region for current, begins linearly increasing just after 0V (needs to pass threshold voltage for some current)
What does a perfect ammeter have (in series)? Why do we want this?
zero resistance
so that their is minimal resistance added to the circuit when using an ammeter, so the current can be accurately measured.
What does a perfect voltmeter have (in parallel)? Why do we want this?
Infinite resistance
So that it doesn’t pull any current from the circuit in order to obtain an accurate measurement of the voltage of a component.
How are resistance and length related? Why?
proportional
it is like putting two resistors in series
How are resistance and cross-sectional area related? Why?
inversely proportional
it is like putting two resistors in parallel
How are resistance and resistivity related?
proportional
When is resistivity constant?
at a constant temp
what resistivity do good conductors have?
small
what resistivity do good insulators have?
large
Why does the resistivty of metals increase with temp?
The metals’ atoms (which all have free electrons) are vibrating.
The higher the temp, the higher the energy these vibrations have.
For current to flow, free electrons need to pass through the gaps between the metal atoms.
At higher temps, there are more frequent collisions making it harder for the electrons to pass through.
Why do thermistors act the way they do at higher temps?
They are made of a semiconductor rather than a metal, so at high temps more charge carriers become available
How can superconductors be used? give some examples
to produce strong magnetic fields and reduce energy loss when transmitting electrical power.
the large hadron collider, an MRI scanner
What is the usual range of a superconductor’s critical temp? How is it made to get to this temp?
30K to 90K
by cooling the coils using liquid helium so the current flows continuously and you no longer need the power supply to be on
