Mega Physics Revision Tip

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A-level Physics By: Please log in to see tutor details
Subject: Physics » A-level Physics
Last updated: 17/05/2018
Tags: equations, exams, physics, revision, units

Are you finding it impossible to remember all those equations and units of measurement for your physics exam? You're not alone and why aren't you just given all the equations? It's not a memory test after all. Well I totally agree that most equation are 'Google-able', however, for the sake of speed and understanding it does help to memorise some of the common ones.

Thankfully there's a simple trick that helps with most (but not all!) equations. This trick helps you to find units of measurement when given an equation and helps to find equations from units of measurement. 'Come again?' It's easier if I use an easy and common example:

Let's say you can't remember the equation speed = distance/time. We all know that speed can be measured in miles per hour, or if you prefer - metres per second. Here's the cool thing. That word 'per' means 'divide'. By saying 'metres per second' we're really saying 'a distance (metres) divided by a time (seconds).' And there you have it: speed = distance/time.

It works the other way round too. Let's say we're given the equation relating energy, mass, specific heat capacity and a change in temperature: E = mcT (T can be changed to theta, delta theta or even a smiley face if you really want, as long as you state what each symbol means. After all they're just labels).

An exam question may ask you to find a specific heat capacity c. I'll rearrange the equation for you to get c = E/mT. Now imagine after you plug in your given numbers and get an answer, you can't remember for the life of you what the units for specific heat capacity are. Look at the units you're given for energy which is J, mass which is kg and temperature change which is degrees celsius. Now look at the equation c = E/mT and remember β€˜/β€˜ or β€˜per’ means divide. Using the given units in place of the original letters we have J/kg degreesC (I used words here in case of formatting errors but better to use a degrees symbol).

When doesn't this method work? If you try finding the units for Power = energy/time or P = E/t you'll get joules/second (or J/s). This is fine actually and perfectly correct though by convention we tend to use units of Watts for power. Think of if as an abbreviation.

I should just say that's some units are worth just knowing e.g. energy is measured in Joules, but the above tip is a life-saver for some of those more complicated units and equations.

Andy R GCSE Maths Tutor (Canterbury)

About The Author

Hi. I'm Andy. I'm based in Herne Bay but come out to students or can teach online. My style is informal and relaxed.

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