A lamp has a rating of 18V 9W. How much energy is transferred to the bulb in 5 minutes? Calculate the current through it when connected to a 18V supply.

  • Google+ icon
  • LinkedIn icon

The first question comes from the realisation that the power rating, "9W" represents 9 joules being supplied every second and so can be written as 9J/s and so in 5 minutes (or 300 seconds) the energy supplied is:
9J/s * 300s = 2700J 

The second part comes from the equation P=IV and we already have numbers for power and voltage:
9 = 18 * I 
I = 9/18 = 0.5Amps

Alexander N. GCSE Physics tutor, IB Physics tutor

About the author

is an online GCSE Physics tutor with MyTutor studying at Durham University

Still stuck? Get one-to-one help from a personally interviewed subject specialist.

95% of our customers rate us

Browse tutors

We use cookies to improve your site experience. By continuing to use this website, we'll assume that you're OK with this. Dismiss