resistance and resistivity Flashcards
Why use gold in circuits
Excellent conductor
number density almost as high as copper
much less reactive so corrodes very little over time
used in high energy electrical applications
and fine wires that connect pins on computer chips to integrated circuit boards
4 factors of resistance
Temperature
Material
length of wire
cross sectional area of the wire
Is resistance or resistivity unique
resistivity of a material is unique
ie copper has a unique resitivity
what does term resitivity mean
used to describe electrical property of material
What happens to PD and RESISTANCE when length of wire doubles
and whats proportionality of resistance and length
PD doubles too x2, So resistance doubles
restiance proportional to length
What is relationship between Resistance and length in terms of poroportionality
Resistance is directly proportional to length
What happens if cross sectional area of wire increases
resistance decreases
Whats proportionality relationship between resistance and cross sectional area
Resistance is inversly proportional to 1/A
R= 1/A
What is the equation for restitivity and resistance and the name of the symbol for restitivity.
and significance of each letter in equation
R = PL/A
P= RA/L
p is rho symbol
R is resitance
A is area
L is length
What is resitivity measured in
ohm metre
what is the equation needed to calculate cross sectional area
pie r squared
What happens to resitivity when temps increase
Resistivity increases
How to do resitivity experiment
- Make a circuit with terminal, ammeter,voltmeter
- Use a piece of wire, and investigate restistance by changing the length of wire, and see the PD across those lengths and the current to get Resistance
how to determine resistivity from the values obtained from experiment
- First draw line, it will be a linear line through origin. Y axis is resistance R, x axis is length/m
- Get gradient
- Gradient = R/L
- Gradient x cross sectional area of wire = resitivity
What is superconductivity
When material gets colder, their resistivity drops as expected. But then at a critical temperature the resistivity suddenly falls to 0.
do components made of superconducting material have electrical resistance
And the effect of this
No, which is why huge amounts of current passes through them.
What is the typical temperature at which wires become superconducting
4 Kelvin = -269 celcius
What is the typical temperature for superconductors
4 Kelvin = -269 celcius
What is the difference between resistance and resistivity
Resistivity is a property of a material that only changes if temperature changes. Measured in ohm metres
Resistance is dependant on resisitivity ie material, area and length of component. measured in ohms
