Effect of Temperature on the Resistivity of a Wire Flashcards
why doesnt ohms law apply to a filament lamp
because the temperature of the filament rises as the current increases
what does this therefore mean about the relationship between the resistance and temperature
the resistance increases as the temperature rises
ive already gone through this but we’ll do it again. why does the resistance increase as the current increases
- when the temperature of the metal is raised, due to collisions between the free electrons and the lattice of positive ions, the ions gain more kinetic energy
- this causes the amplitude of their vibrations to increase
- leading to an increase in the interactions between the lattice and the electrons
what is the equation for current with drift velocity in it
I = nAvq
what are the two constants in the equation for any wire
- A, the cross-sectional area
- and q, the charge of each charge carrier
- this is because they dont change at different parts of the wire
what is another constant in the equation if you were using a metallic conductor
- n, the number of charge carries per cubic meter
- as n wouldnt depend on the temperature
what would happen to the current in this equation if the temperature were to be increased and why
- the current would decrease
- this is because the drift velocity of the electrons would decrease
- due to the increased amplitude of the vibrations of the lattice of ions
- and as n, A and q are constant, I will decrease
how would this all tie up to further confirm that an increase in temperature leads to an increase in resistance
- if you use R = V / I
- a constant V with a smaller I from I = nAvq would lead to a smaller denominator
- and therefore a larger resistance
what does it mean if a material has a PTC
- a positive temperature coefficient
- it means that if the temperature increases its resistivity increases
