Safety :- For safety reasons i will make sure that i dont touch the filiament bulb because it can become very hot, also i must make sure the circuit is wired up properly
Method :-Firstly I am going to set up the circuit (Fig 1) I will then start by postioning the variable resistor at it’s lowest point then move it constantly every time I move it I will read what the voltmeter and ammeter say and note them done I will leave the power pack on Volts.
I will then plot the results on a graph. my reason for doing this is to find out If
the filiment bulb obeys ohms law and to work out the resistance. Finally I will not reapeat the test because, it would not be fair to, due to the fact that i can not always postion the variable resisotor in the same place.
Prediction :- I belive the resistance will vary with the increase of temperature. I think this because my componets have a fixed value of resistance only if the tempertaure stays the same. If the temperature increases, the paficies in he wire will vibrate making it harder for electrons to pass though because resistance increases. The more power the lamp gets. the hotter it becomes. i predict that my results will not obey ohms law due to the the temprature changing.
Below is a graph that displays something that obeys ohms law. For a conductor at constant temprature the current in the conductor is proportional to the voltage accros it.
Below is the a prediction of what my graph should look like
This is because current and voltage is not porportional so that why i have a curve abd this does not obay ohms law.
I belive my graph will look like (fig 3) because when the temprature is low the electrons can easily pass though the possitive ions (fig 4). But when the temprature is increased the ions vibrate making it more diffcult for the electrons to find it's way though the wire (fig 5), this is what producers heat when the electrons collide with ions they produce heat, which makes the ions vibrate this also casuse powerloss. this makes the current and voltage not proprtional suggesting that it should not follow ohms law. For the recored if the wire was thicker it would make it alot easyer for electrons to pass making the curve in (fig 4) more stright. This is called Resistivity
If length and area is constant, resistivity will change the resistance in a circuit because when the temprature is low the electrons can easily pass through the posstive ions
Analaysis :- I have found out that as I increased the variable resistor and went over the readings they showed that the voltage and current was not proptional showing that the filiament bulb does not obey ohms law and resistance increased. when i compare this with my prediction i can see that it did not obeys ohms law due to the temprature increase in the bulbs filiment, my prediction was pretty acurate. my graph shows that the filiment bulb did not follow ohms law this is because of restivity is..
Resitivity :- the resistance of a wire depends on the length, size and shape. a long wire has more resistance because it finds it harder to get though, due to is hitting more ions.
A thicker wire has less resistance than a thin wire. Because is has more space to get though, thus not hitting as many ions. The resistance also depends on what material it is made of, copper for exaple is a better conductor than steal but steel is better than silicon.
To work out resistance resistance we need to take into account, the length,area,shape and the material. Resistivity is the relevant property of a material. the symbol is; P (Greek- letter R)
OR
Evaluation :- I found it easy to wire the circuit and take results although, it was hard to understand resitivity. My results came out find i did not find one anomaloys result but if I had it could be down to the use of a diffrent bulb the variable resistor had been moved to far or to less, the room tempreature could make a slight diffrent. if i had more time i would have changed the voltmeter and not the resistor and reapeted the experiment.
