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?

Thanks in advance!

Reply 1

teachercol

9

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

Reply 2

Faith01

10

sounds like you know your stuff, exam is tomorrow (AQA), Ill need to do really good in that before i flop unit4 :frown:

Reply 3

Ezraeil

15

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?

Reply 4

Mr Nonsense

OP

13

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!

Reply 5

Ezraeil

15

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.

So in your answer,just say the temperature rises,rather than saying stuff about "heating effect" etc.

Reply 6

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?

Reply 7

Stonebridge

13

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.

Reply 8

Dipesh97

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

https://www.google.co.uk/search?q=led+graph&source=lnms&tbm=isch&sa=X&ei=3D2rUtymD6vB7Aa_zoEY&ved=0CAcQ_AUoAQ&biw=1024&bih=718#facrc=_&imgdii=_&imgrc=9xVCG-DaVG4AuM%3A%3BGfvxcDMF4Dk6tM%3Bhttp%253A%252F%252Fphysicsnet.co.uk%252Fwp-content%252Fuploads%252F2010%252F06%252FVI-graph-for-filament-diode.jpg%3Bhttp%253A%252F%252Fphysicsnet.co.uk%252Fgcse-physics%252Fnon-ohmic-devices%252F%3B250%3B249

Reply 9

Stonebridge

13

Original post by Dipesh97

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

https://www.google.co.uk/search?q=led+graph&source=lnms&tbm=isch&sa=X&ei=3D2rUtymD6vB7Aa_zoEY&ved=0CAcQ_AUoAQ&biw=1024&bih=718#facrc=_&imgdii=_&imgrc=9xVCG-DaVG4AuM%3A%3BGfvxcDMF4Dk6tM%3Bhttp%253A%252F%252Fphysicsnet.co.uk%252Fwp-content%252Fuploads%252F2010%252F06%252FVI-graph-for-filament-diode.jpg%3Bhttp%253A%252F%252Fphysicsnet.co.uk%252Fgcse-physics%252Fnon-ohmic-devices%252F%3B250%3B249

The idea is YOU write what YOU think is an explanation, and WE give you some feedback and help you improve your answer if necessary. Just like the first poster did 4 years ago.