StemUp: OCR A A level Physics 2.1: Physical quantities and units

What is meant by a physical quantity? (1)

A physical quantity is a property of an object or phenomenon that can be measured.

What is the difference between a quantity and a unit? (1)

A quantity is what is being measured (e.g. mass or force), while a unit is the standard used to express its value (e.g. kg or N).

What are the SI base quantities and their units? (6)

- Mass, kg

- Length, m

- Time, s

- Current, A

- Temperature, K

- Amount of substance, mol

How do you deduce the derived units of physical quantities in terms of SI base units? (2)

- Write an equation for the physical quantity using other measurable quantities.

- Replace each quantity with its base unit and simplify.

How do you check if an equation is homogeneous using SI base units? (2)

- Substitute the base units into both sides of the equation.

- If the simplified units are the same on both sides, the equation is homogeneous.

What prefix and order of magnitude is represented by each of the following: P, T, G, M, k, d? (6)

- Peta (P): 10^15

- Tera (T): 10^12

- Giga (G): 10^9

- Mega (M): 10^6

- Kilo (k): 10^3

- Deci (d): 10^-1

What prefix and order of magnitude is represented by each of the following: c, m, μ , n, p, f? (6)

- Centi (c): 10^-2

- Milli (m): 10^-3

- Micro (μ): 10^-6

- Nano (n): 10^-9

- Pico (p): 10^-12

- Femto (f): 10^-15

What are two examples of physical quantities with the same derived units? (2)

- Stress and pressure: both have units of kgm^-1s^-2

- Work done and moment: both have units of kgm^2s^-2