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: In a [[Filament Bulb|filament]] '''bulb''' [[Electrical Work|electrical work]] is done to [[heat]] the filament to a high enough [[temperature]] that it glows in [[Visible Light|visible light]], see [[Black Body Radiation|black body radiation]].
: The [[Electrical Current|electrical current]] has a [[heating]] effect on the filament which increases its [[temperature]]. This causes the [[Electrical Resistance|resistance]] to increase, so the '''bulb''' does not behave as an [[Ohmic Conductor|ohmic conductor]].
===IV Graph===
{| class="wikitable"
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|[[File:IVGraphBulb.png|center|400px]]
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| style="height:20px; width:200px; text-align:center;" |
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====Description====
The [[IV Graph]] for a '''bulb''' shows that:
*As [[Potential Difference|potential difference]] increases, [[Electrical Current|increases]].
*At small [[Potential Difference|potential differences]]] the the relationship between [[Potential Difference|potential difference]] and [[Electrical Current|current]] is [[linear]] (the [[gradient]] is constant).
*At large [[Potential Difference|potential differences]] the [[gradient]] becomes more shallow as the [[Electrical Resistance|resistance]] of the '''bulb''' increases.
====Explanation====
: At small [[Potential Difference|potential differences]] there is a small [[Electrical Current|current]] so the [[heating]] effect of the [[Electrical Current|current]] is small and the [[filament]] remains at a low [[temperature]].
: At large [[Potential Difference|potential differences]] there is a large [[Electrical Current|electrical current]] so the [[heating]] effect of the [[Electrical Current|current]] is large which causes the [[filament]] to be a high [[temperature]].
:: This is caused by [[electron]]s in the [[wire]] [[collide|colliding]] with [[ion]]s in the [[metal]] [[lattice]] causing them to [[vibrate]].
: [[Wire]]s (like the [[filament]]) have a greater [[Electrical Resistance|resistance]] at higher [[temperature]]s, causing the increase in [[Electrical Current|current]] to be reduced.
:: This is because the more the [[ion]]s in the [[metal]] [[lattice]] [[vibrate]] the more likely [[electron]]s are to [[collide]] with them and slow down.