2. SI Units

Question 1

Intro spiel

who / why invented them

whats the benefit

Answer 1

The creation of the decimal metric system began during the eighteenth-century French revolution when two platinum standards, representing the metre and kilogram, were placed in the Archives de la République in Paris.

Eminent scientists like Gauss and Weber then went on to promote the universal application of a standard system of measurement in the early nineteenth century.

By the 1960s, the International System of Units (abbreviated to SI units from the French Le Système International d’Unités) was developed which incorporated six base units (the mole was added later) along with rules for the use of derived units and prefixes. The advantage of this unified system is that equations and calculations will produce answers in the appropriate SI unit. Unfortunately, they are not used universally.

A question concerning the SI units is a popular opening to the physics SOE and candidates should understand the relationship between derived and base units and be comfortable in manipulating them from one to the other.

Question 2

SI Units

Answer 2

Base unit Name Symbol
Length              metre m
Mass                 kilogram kg
Time                  second s
Current              ampere A
Temperature     kelvin K
Am of sub         mole mol
Lums intens     candela cd

Question 3

What are the two

supplementary units?

Answer 3

The plane angle (radian) and solid angle (steradian) were supplementary units
but this category was abolished in 1995. These units are considered named
derived units.

Question 4

List some of the derived units

Answer 4

Derived units are formed by combination of
various base units according to
mathematical relationships
which link these quantities.

Derived units Name Symbol
Area square metre m2
Volume cubic metre m3
Density kilogram per cubic metre kg/m3
Velocity metre per second m/s
Acceleratrion metre per second squared m/s2

Question 5

Derived Named SI UNITs

Answer 5

Force

Pressure

Energy

Power

Electric charge

Electric potential difference

Capacitance

Electrical resistance

Magnetic flux

Magnetic flux density

Inductance

Question 6

Pressure

Answer 6

Pressure pascal (Pa) N/m2 kg·m–1·s–2

Question 7

Energy

Answer 7

Energy joule (K) N·m kg·m2·s–2

Question 8

Power

Answer 8

Power watt (W) J/s kg·m2·s–3

Question 9

Electric charge

Answer 9

Electric charge coulomb (C) – A·s

Question 10

Electric potential

difference

Answer 10

Electric potential difference

volt (V) W/A kg·m2·s–3·A–1

Question 11

Capacitance

Answer 11

Capacitance farad (F) C/V kg–1·m–2·s4·A2

Question 12

Electrical

resistance

Answer 12

Electrical resistance

ohm (Ω) V/A kg·m2·s–3·A–2

Question 13

Magnetic flux

Answer 13

Magnetic flux

weber (Wb) V·s kg·m2·s–2·A–1

Question 14

Magnetic flux

density

Answer 14

Magnetic flux density

tesla (T) Wb/m2 kg·s–2·A–1

Question 15

Magnetic flux density

Answer 15

Magnetic flux density

tesla (T) Wb/m2 kg·s–2·A–1

Question 16

Inductance

Answer 16

Inductance henry (H) Wb/A kg·m2·s–2·A–2

Question 17

Temperature

Answer 17

Temperature degree celsius (°C) – K

Question 18

Bigger SI Unit prefix

Answer 18

Factor	Name 	Symbol
1024	yotta	Y
1021   	zetta	Z
1018 	exa	         E
1015 	peta	P
1012 	tera	          T
109  	giga	        G
106  	mega	M
103  	kilo	        k
102	       hecto	h
101    	deka	da

Question 19

Smaller SI Unit prefix

Answer 19

Factor	Name 	Symbol
10-1	        deci	           d
10-2	        centi	    c
10-3	        milli	          m
10-6         micro	    µ
10-9  	nano	   n
10-12	pico	            p
10-15	femto	    f
10-18	atto	            a
10-21	zepto           z
10-24	yocto           y