2 Determine the Electrical Resistivity of a Material Flashcards
how do you measure the cross sectional area of a thin wire
using a micrometer measure the wire diameter in at least three different places along the wire. use the average in the circular area equation
how can the length of wire be varied when carrying out this experiment
one end of the wire can be fixed whilst the other end can be connected to the circuit using a crocodile clip. the length of conducting wire can be varied by changing the position of the clip
what device is used to measure the current across the wire and how is it connected
and ammeter which should be connected in series with the wire
what device is used to measure the potential difference across the wire, and how is it connected
a voltmeter which should be connected in parallel across the wire
why does the resistance of a wire increase as its temperature increases
as temperature increases the metal ions gain kinetic energy and so they vibrate more. these vibrations make it harder for charge carriers to pass through the wire and so resistance increases
why should he temperature of the wire remain constant throughout the experiment
temperature variations can effect the resistance of the wire. in this experiment temperature is a control variable
why should the power supply be switched off between readings
the temperature of the wire should remain constant throughout the experiment. switching the supply off between readings will mitigate the heating of the wire, during the experiment
how can the resistivity of a wire be determined from a graph of resistance against length
the gradient of the graph will be R/L and so multiply the gradient by the cross sectional area should give the resistivity
why should he current used in this experiment be kept low
as current increases temperature increases, by keeping the current low the heating effect on the wire is minimal
how can you ensure that the length measurements are taken from the same place each time
a meter ruler could be taped in place below the wire
what factors lead to uncertainties in the experiment
there will be resistance between crocodile clips and the wire swell as the constant of the leads and the power supply. there may also be a zero error due to the positioning of the ruler and crocodile clip at the zero end
what device could replace the voltmeter and ammeter in this experiment
a multimeter could be used to measure the voltage, current and resistance. this may lower the resolution of the data dependent on the number of significant figure provided by the devices you have available
