A torch uses 15watts of energy. It uses two 1.5volt batteries connected in series. What is the resistance in the circuit of the torch?

In order to answer this question, we need a formula which relates resistance to voltage and power. We don't already know this formula, but can create it from two formulae we already know: P=IV & V=IR. As we do not know what the current is, we can remove it from these equations using the elimination method. In this case, that means dividing one forumla by another. This gives us a new formula: P/V=V/R. We want R to be the subject of the formula, so we can rearrange, using algebra, to make: R=V2/P. We can now work out the resistance.

Remember that the voltage is 3, as we have two 1.5 volt batteries connected in series, which means their voltages are added. Substituting these numbers into the forumla give R=0.6Ω

HW
Answered by Hugo W. Physics tutor

2011 Views

See similar Physics GCSE tutors

Related Physics GCSE answers

All answers ▸

In the photoelectric effect, why is the kinetic energy of the electrons independent of the intensity of light?


What is terminal velocity?


explain the relationship between resistance and voltage in a filament lamp


What does a velocity-time graph represent?


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences