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ConquerYOUR A LEVELS

Derived Units & Homogeneity

The trolley's distance is measured in metres and its time is measured in seconds. Therefore the calculated speed has the unit:

These examples use relations taught later in the course. At this point, a question may supply the relation; focus on replacing each quantity with its base units.

Express the ohm in SI base units. Use resistance = potential difference ÷ current and potential difference = power ÷ current.

The units match, so the equation passes the homogeneity check. This does not prove that the numerical factor or physical model is correct.

A mass hangs on a spring with spring constant kk. Test whether T=2πm/kT = 2\pi\sqrt{m/k} is homogeneous.

Practise Physical Quantities and Units
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