Problem: Find the current that flows through the filament of a 400 Watts flat iron connected to a 220 volt power line.

Attempt: The only formula I could think of that will connect voltage and current is P = I*V, which results to I = (400) / (220) = 1.82 A.

Sadly, the answer is 500 mA. The question is how? Any help would be appreciated.

  • 2
    \$\begingroup\$ Obvious error in web answer , unfortunately \$\endgroup\$ May 25 '18 at 4:30
  • 1
    \$\begingroup\$ To confirm, P=IV, so your method of I=P/V = 400/220 = 1.82A was totally correct in using the right formula, doing the calculation correctly, and rounding to a reasonable number of significant figures for engineering. Well done. \$\endgroup\$
    – Neil_UK
    May 25 '18 at 5:28
  • 1
    \$\begingroup\$ Don't visit that site again! \$\endgroup\$
    – Chu
    May 25 '18 at 10:28
  • \$\begingroup\$ +1 for asking the question. It's sometimes difficult to know whether published information is saying something you don't understand, or flat out wrong. Here, it's flat out wrong. Probably useful to post the URL as a warning to others. \$\endgroup\$ May 25 '18 at 12:34

I get 1.82 Amps (not V), so it seems that the 500 mA answer you were given is wrong.

  • \$\begingroup\$ Sorry, that was an error, should be in Amps. There are many references that showcase 500 mA is the answer, sadly it doesn't show solution only the right choice out of 4 given choices. \$\endgroup\$
    – Jayce
    May 25 '18 at 3:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.