1. ### Imperial units

America is mostly leading in science, especially in astronomy, yet they still use imperial units. (I am not talking about the great people doing the science.) Everyone else is using SI and the metric system however they insist on using miles, yards, pounds, feet, etc., and continue on being a...
2. ### I SI definition of second: what day/year is the reference year

The SI definition of a second was originally based on 1/86 400 of a day - but the earth's rotation is a) unsteady and b) changing so it was changed to a defined number of cycles of an atomic clock. Was there a specific day for which the atomic clock was calibrated? Put another way, why were 9...
3. ### B Dimension of the electric charge in CGS and in SI?

The Bohr magneton is (see e.g. Wikipedia) in SI units: $$\mu_B=\frac{e\hbar}{2m_e}$$ and in CGS units: $$\mu_B=\frac{e\hbar}{2m_ec}$$ So the dimension of the electric charge in SI, ##[q_{SI}]##, is related to the dimension of the electric charge in CGS, ##[q_{CGS}]##, by...
4. ### Dimensionless units

The topic has been discussed before at PF, in particular @haruspex's Insight Can angles be assigned a dimension? Nature has now published an editorial on the subject: SI units need reform to avoid confusion
5. ### Multiplying epsilon naught by a length quantity

Homework Statement Note that this formula (##C=4 \pi \epsilon_0 R##) and the others we have derived for capacitance involve the constant multiplied by a quantity that has the dimensions of a length. Homework Equations ##\epsilon_0## has the following units in SI: $$\frac {C^2} {N \cdot m^2}$$...
6. ### How to etch (100) p-tye Si

Im trying to etch 525um (100) p-type silicon, and i intend to use HF+HNO3+CH3COOH for high etching rate since i need to etch 525um of Si. does anyone know what ratio should i use to obtain high etching rate? I am trying to look for a mask that is able to withstand the attack of the etching...
7. ### I Cgs to SI unit conversion

Hi I have a value that is 10.7 mJy, that I need to convert to SI units. I thought it would be 1.7*10^(-2)*10^(-26) but that might be wrong? Then I have a flux value, kappa, of 2 cm^2.g^(-1) that needs to be converted to meters and kilogram. I thought it was 2*10^(-7) m2/kg, but that might be...