General

Question 1

What is the SI system of measurement?

Answer 1

• Internationally agreed system defines 7 base quantities and their units.
• Definitions are based on specific physical measurements that can be accurately reproduced in labs across the world.
• Kilogram is an exception. This is the mass of a particular metal cylinder - the prototype kilogram - which is kept in Paris.

Question 2

What are the base quantities and units?

Answer 2

• time (t)/s
• length (l)/m
• mass (m)/kg
• temperature (T or θ)/K
• electric current (I)/A
• amount of substance (n)/mol
• luminous intensity/cd

Question 3

Prefixes?

Answer 3

10^12 - tera/T
10^9 - giga/G
10^6 - mega/M
10^3 - kilo/k
1
10^-3 - mili/m
10^-6 - micro/μ
10^-9 - nano/n
10^-12 - pico/p
10^-15 - femto/f

Question 4

Conversions?

Answer 4

1m^3 = 10^6cm^3 = 10^9mm^3

Question 5

What is a physical quantity?

Answer 5

• Anything measurable.
• Always have a size and usually a unit.
• Can be a ratio/number e.g. % efficiency, magnification
• 7 base units (S.I units).

Question 6

What is a derived quantity?

Answer 6

• They don’t have their own units.

e. g. v = s/t, V = lxbxh, ρ = m/V, etc.

Question 7

Examples of a derived unit?

Answer 7

N = kgms^-2
units of force = units of mass x units of acceleration
= kg x ms^-2
Pa =kgm^-1s^-2
units of pressure = units of force/ units of area
= kgms^-2 x m^-2
J = kgm^2s^-2
units of work done = units of force x units of distance
= kgms^-2 x m

Question 8

What is dimensional analysis?

Answer 8

• Using S.I units to describe the unit of a derived quantity.
• It uses homogeneity (uniformity) in physics equations.

Question 9

Dimensional analysis for the time period of a simple pendulum?

Answer 9

What affects:
-T, time period
-l, length
-m, mass
-g
T = l^a x m^b x g^c
T = k√l/g