# Filament Lamp I-V- Curve

So this is the I-V characteristic for a filament lamp:

So what is the best answer for the question where you have to "explain the shape of the I-V characteristic for a filament lamp", typically 4 - 5 marks??

This is what I have:

Initially - with positive potential differences - the current is directly proportional to the p.d. However, as the current through the filament increases, the heating effect caused in the lamp also increases and so the temperature of the filament rises. This increase in the filament's temperature also increases the resistance of the filament. As a result the rate of increase of the current decreases and a greater change in the potential difference is required to cause a change in the current. This can be seen on the curve as the gradient becomes more shallow (greater resistance). This same pattern is repeated when a negative potential difference is applied across the filament.

So how can I improve this answer? Is it correct? Is there anything that i have missed?

Looks fine generally - I'd refer to the gradient rather "the rate of increase of current".
sounds like you know your stuff, exam is tomorrow (AQA), Ill need to do really good in that before i flop unit4
Yeah...that'd get you all the marks im pretty sure...try and shorten it a bit maybe to save time in the exam...You doing AQA Physics A?
SyedT
Yeah...that'd get you all the marks im pretty sure...try and shorten it a bit maybe to save time in the exam...You doing AQA Physics A?

yeah - i find the questions so vague in the exams generally (not this question though).

Which bits do you think i could chop then to make it shorter?

teachercol
Looks fine generally - I'd refer to the gradient rather "the rate of increase of current".

ok, so the "rradient decreases indicating that a larger change in the p.d. is required to cause a change in the current (i.e. greater resistance)"??

thanks everyone!
Well...my answer would be something like:

Initially I is proportional to V. As the current is increased,the temperature of the filament increases,which leads to an increase in its resistance.This then leads to the current and voltage not increasing proportionally. The same pattern is repeated when a negative P.D is applied.

If there was a similar question asking the same but for a resistor at constant temp and an LED, how would you write this?
Original post by Dipesh97
If there was a similar question asking the same but for a resistor at constant temp and an LED, how would you write this?

This thread is 4 years old!

The question is asking you to explain the shape of a graph.
You need to provide the graphs if you want an answer. The graph will not be the same shape as the one in the 1st post.
Original post by Stonebridge
This thread is 4 years old!

The question is asking you to explain the shape of a graph.
You need to provide the graphs if you want an answer. The graph will not be the same shape as the one in the 1st post.

How would you, in the way the filament lamp was described, describe the graph for
1. A resistor at constant temperature

http://jcsu.jesus.cam.ac.uk/~rpc25/notes/physics/electricity/charac1.gif

2. An LED