How do you work out the work out the current through resistors in parallel?

[I would use the whiteboard to draw diagrams as I was talking]
A good analogy for circuits is that of water pipes. The wires are nice wide pipes with no resistance to flow. Resistors are sections of narrow pipe that restrict flow. A pressure difference (a.k.a. voltage) is needed to push water through these narrow sections. Really small pipes require high potential differences to push water through at the same rate - this is the origin of the equation V = IR.
What would happen if you get two pipes next to each other? [work through logic with student: answer is that the effective pipe width doubles]. The "effective pipe width" is called conductance, and is equal to 1/R. From the diagram, it is clear to see you simply add these conductances together, which is what you do in circuits: 1/R = 1/R1 + 1/R2. This will give you the overall conductance, and you take the reciprocal to get the resistance!

Related Physics A Level answers

All answers ▸

A car is travelling at 10m/s when it brakes and decelerates at 2ms^-2 to a stop. How long does the car take to stop?


What are the differences between standing waves and progressive waves?


A pellet of mass 8.8 g embeds itself in a wooden block of 450 g which is suspended by a light in-extensible string. After the collision the block reaches a max height of 0.63 m. Calculate the initial velocity of the pellet.


A cricketer throws a ball vertically upwards so that the ball leaves his hands at a speed of 25 m/s. Calculate the maximum height reached by the ball, the time taken to reach max. height, and the speed of the ball when it is at 50% max. height.


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2024

Terms & Conditions|Privacy Policy
Cookie Preferences