Will a 60-watt bulb produce a greater rise in temperature than a 25-watt bulb? If so why?I am helping my 11-year-old granddaughter with her science fair project. She needs to know how a light bulb...

Will a 60-watt bulb produce a greater rise in temperature than a 25-watt bulb? If so why?

I am helping my 11-year-old granddaughter with her science fair project. She needs to know how a light bulb works.

Expert Answers
enotechris eNotes educator| Certified Educator

Higher wattage will produce a higher temperature, if time remains constant. A lightbulb works because electrons flow through the wire, and through the thinnest part inside the bulb, called the filament.  Because the filament is in a vacuum or surrounded by something other than air, it doesn't burn, it glows, giving off light and heat.  If your granddaughter has access to a laboratory thermometer, she can prove this experiment:

A Watt equals a Joule/second, or an amount of energy per unit time.  4,180 Joules will cause 1 Kilogram of water to increase its temperature 1 degree C.  So if she places a 25 watt bulb near a container of water, it'll take an amount of time to raise the temperature.  A 60 watt bulb will take less time to raise the temperature the same amount, or will raise the temperature further if allowed to emit for the same amount of time as the first lightbulb.  So for a 25 Watt bulb, 4180 Joules / 25 Joules per second = 167.2 seconds.  So every 167.2 seconds, the temperature of the water will increase 1 degree C.  For a 60 Watt bulb, 4180 / 60 Joules per second = 69.6 seconds, so every 69.6 seconds the temperature of the water will increase 1 degree C.  If she keeps the bulbs shining for 300 seconds (5 minutes) the temperature increase will be 1.8 C for 25 Watts and 4.3 C for 60 Watts.  Have fun!