Why Does a filament give off Light?

A light bulb is “turned on” by passing an electric current through its filament, heating the filament until it is “white hot.” The high temperature of the filament--up to 3,000 oC, causes it to give off visible light by a process called incandescence. 
Incandescence is defined as the emission of visible light by a hot body. Any hot object gives off incandescent light. The higher the temperature of the object, the brighter the light given off. Examples of incandescent objects include hot coals in a campfire or barbecue grill, the sun, light bulb filaments and the burners on electric stoves, which glow dull red when their temperature is on high. Electric stove burners are just above the minimum incandescence temperature visible to the human eye, about  (390 oC).

In describing incandescence, most temperatures are given in degrees Kelvin (K). The Kelvin temperature scale is directly related to the Celsius scale given in degrees centigrade (oC) by:
         T (K)  =  T (oC) + 273.15

The Fahrenheit temperature scale is also directly related to the Kelvin scale 
         T (K)  =  (5/9)T(oF) + 255.37

Use the Interactive Thermometers to explore the relationship between Kelvin (K), Centigrade (oC) and Farenheit (oF) scales as water changes from ice to water to gas. Also investigate the broader Interactive Temperature Scales which range up to and beyond typical light bulb filament operating temperatures.

After you have explored the applets, take the following quiz. You can always go back and experiment with the applets, to answer the questions.

 
 
Question 1

 Which temperature scale(s) start at zero?

Centigrade scale
Kelvin scale
Fahrenheit scale
none of the above

 
Evaluation of your response for Question 1

Good. The Kelvin scale is the scale which begins at zero. Incidentally, we can never reach this absolute 0 K , as it is forbidden by the Third law of Thermodynamics.

 
Evaluation of your response for Question 1

Try again! Please see the applet to select the correct response.

 
Question 2

Which scale(s) have negative temperatures?

Centigrade scale only
Kelvin scale only
Fahrenheit and Centigrade scales
Fahrenheit scale only

 
Evaluation of your response for Question 2

Very Good! Both the Fahrenheit scale and Centigrade scale have negative temperatures.
The Kelvin scale on the other hand does not have negative temperatures, as it is an absolute scale based on Charles' Law

 
Evaluation of your response for Question 2

Try again! Please see the applet to select the correct response.

 
Question 3

You know that water boils at 100 oC/212 oF.
At what temperature, in K, does water boil? 

373 K
473 K
573 K
none of the above

 
Evaluation of your response for Question 3

Good! The closest answer is 373 K. To be
precise, water boils at 373.15 K, at a pressure of 1 atm. 

 
Evaluation of your response for Question 3

Try again! Please see the applet to select the correct response.

 
Question 4

If you know that a light bulb filament first begins to emit light at 390 oC/734 oF, what then is the temperature, when expressed in K?

563K
463 K
763 K
663 K

 
Evaluation of your response for Question 4

Yes. The correct answer is 663 K. You have finished the quiz, please go on to the next section.

 
Evaluation of your response for Question 4

 Try again! Please see the applet to select the correct response.

SYNOPSIS

1)Kelvin scale begins at zero

2)Fahrenheit and Centigrade scales have negative temperatures
3)Water boils at a temperature of 373 K.