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This tool provides you with a database of some common constants used in chemistry and physics. All constants are the official NIST values.
Provided you haven't changed any settings, you should see a table of constants with four columns - constant name, symbol, value and units.
Constants are organized into categories. You can switch between categories by tapping the blue gear button on the command bar. In some categories constants are divided into groups. Tapping a group title will expand or collapse the group. There is also a button on the command bar (the one with a pair of boxed plus and minus signs) to expand or collapse all groups in the category.
You can show or hide category title by pressing the command bar button with red bar at the top. This will give you more space to work with.
Understanding constant value
Almost every value in the database contains its uncertainty as part of the value. The one or two digits in brackets at the end of the value indicate, respectively, the standard uncertainty in the last one or two digits of the value.
For example, Hartree energy in eV is 27.211 3834(11). This means that the value is 27.211 3834 ± 0.000 0011.
Standard uncertainty basically indicates the range in which the real value is believed to lie with a known confidence level, usually 95%. So we are 95% confident that the Hartree energy is within ±0.000 0011 eV of the given value.
Note also that some constants are now defined. To be more precise, some units are defined in such a way as to fix a physical constant at an exact value. For example, speed of light is fixed at exactly the value it is by the way the meter in SI is defined. See "Definitions of SI base units" below.
The font used to display the table is quite small, and it may be difficult to read the digits correctly.
If you need a larger view of a constant, tap it with your stylus. The constant will become highlighted, and a zoom box will appear at the bottom of the screen. If the constant doesn't fit, you can drag around in the box the usual way.
You can show or hide the zoom box by pressing the command bar button with red bar at the bottom. You can also tap the zoom box to hide it.
Some constants have formulae associated with them, which indicate how the constant can be calculated from other constants. There will be a small red arrow displayed in the zoom box in such cases, indicating that you can scroll down to see the formula.
Adjusting the view
You have some control over what is displayed in the constants table and how it is displayed.
You can select which columns you want to see by pressing the button with a blue gear on the command bar and checking or unchecking the corresponding menu item.
You can change the width of the columns. Tap and hold the stylus over a line separating columns until you see a resize cursor. Now drag the stylus to the desired width.
You can also tap the vertical lines separating columns to automatically adjust column width according to contents.
Currently the view settings are the same for all categories. If you feel that one really needs to remember separate views for each category, send me an email.
I suggest that you use the zoom box to view constant value and hide the value column if you find it annoying that you have to scroll horizontally to see constant value.
Definitions of SI base units
Meter. The meter is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.
Kilogram. The kilogram is the mass of the international prototype of the kilogram.
Second. The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.
Ampere. The ampere is such constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 newton per meter of length.
Kelvin. The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.
Mole. The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.
Candela. The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
These definitions are almost verbatim NIST definitions of SI base units.
|Last updated: 01/07/07||Copyright © 2002-2007 Roman Starkov|