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

2116 Views

See similar Physics GCSE tutors

Related Physics GCSE answers

All answers ▸

Trolley A weighs 5kg and is moving at 15m/s to the right. It collides with a stationary Trolley B, weighing 10kg more than Trolley A. After the collision they move off together. Calulate the velocity that they move off with.


Is momentum a vector quantity? Why?


An electromagnetic wave has a wavelength of 3.0m and a speed of 3x10^8 m/s. State what type of radiation this wave is and calculate the period of the wave.


explain how a parachutist reaches a constant speed using the concept of terminal velocity.


We're here to help

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

MyTutor is part of the IXL family of brands:

© 2025 by IXL Learning