Physics Electricity

I’m studying physics electricity and there are a lot of formulas. I want some ideas of how and what formula to use.


Kia ora Seetai1,

Good question, this is a key part of NCEA Physics and a consistent approach should help you make a start on all of your calculation questions.

I would recommend the GUESS method. I’ll walk you through it below with an example, and link a L1 video example that might help you see how it works.

Example - What voltage would be measured across a 12 ohm bulb, if there was a current of 3.0 Amps through the bulb? (You might find it useful to highlight quantities in the question)

G - Given - write down all quantities (using correct symbols) and values have you been given in the question eg. R = 12 ohms, I = 3.0A

U - Unknown - write down the symbol for the quantity you are being asked to find eg. V=?

E - Equation - look at the equation list and find an equation that includes the unknown and in which every other symbol is one of your given quantities. It might help you to tick terms on the resource sheet until you find an equation in which every symbol is ticked. In our example we would find V=IR covers our given and unknown symbols. You might need to re-arrange the equation to isolate the unknown quantity on one side.

S - Substitute - replace each symbol with its corresponding value. So V=IR becomes V= 3.0 x 12

S - Solve - perform the calculation and write your answer, with appropriate units eg. V = 36 Volts. You should round to an appropriate number of significant figures but I won’t cover that here as it does not relate directly to your question, and you are rarely marked down for it in the exam.

You will be given a copy of the resource sheet in the exam.

Be aware, some merit or excellence questions will require you to use one equation to calculate a value that you then use in a second equation to get your final answer.

I hope that helps. Best wishes for your exam.

Memorizing equations actually kills the joy of learning electricity. Just get some resistors, 4.5 V battery and a DMM a few hookup wires Build simple series and parallel circuits, measure volts, amps, net resistance and then look Ohms laws. All will make sense to you. This is a kind of ‘sticky learning’.

Thank You So Much
This really helps

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