How can a 60W bulb only draw 60W of power if it's internal resistance is 19 ohms? Or does the resistance suddenly increase once the filament heats up?
Thanks.
incandescent bulb power consumption
Oct 29, 2004
7 Replies
Thanks. That makes perfect sense now...
19up?
Oh yea! Typical 5/1, sometimes more.
Yes, considerably. In the UK, with about 235 V mains ac voltage, a 60W bulb would have a hot resistance of about 1k.
Terry Pinnell
Hobbyist, West Sussex, UK
Measuring the resistance of a light bulb is a common elementary circuits class laboratory to get students thinking about resistance as not being particularly fixed. It's very enlightening to many of them!
I believe this site should give you the information for which you are looking. Cheers!
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Your question has been answered in previous posts but for your interest it is precisely that phenomena which is exploited when a small filament bulb is used for amplitude control in a Wein bridge oscillator.
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