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 ▸How can we explain the standing waves on a string?
Why does an α particle cause more ionisation than a β particle if they have the same kinetic energy?
A ball is fired at an angle of 50 degrees with a velocity of 10 ms^-1, at what time does it first hit the floor?
When catching a ball, a cricketer moves his hands for a short distance in the direction of travel of the ball as it makes contact with his hands. Explain why this technique results in less force being exerted on the cricketer's hands