# physconst

Physical constants

## Syntax

`Const = physconst(Name)`

## Description

`Const = physconst(Name)` returns the constant corresponding to the string `Name` in SI units. Valid values of `Name` are `'LightSpeed'`, `'Boltzmann'`, and `'EarthRadius'`.

## Input Arguments

 `Name` String that indicates which physical constant the function returns. The valid strings are not case sensitive.

## Definitions

The following table lists the supported constants and their values in SI units.

ConstantDescriptionValue
`'LightSpeed'`Speed of light in vacuum299,792,458 m/s. Most commonly denoted by c.
`'Boltzmann'`Boltzmann constant relating energy to temperature$1.38×{10}^{-23}$ J/K. Most commonly denoted by k.
`'EarthRadius'`Mean radius of the Earth6,371,000 m

## Examples

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### Wavelength Corresponding to Known Frequency

Determine the wavelength of an electromagnetic wave whose frequency is 1 GHz.

```freq = 1e9; lambda = physconst('LightSpeed')/freq;```

### Thermal Noise Power

Approximate the thermal noise power per unit bandwidth in the I and Q channels of a receiver.

Define the receiver temperature and Boltzmann constant.

```T = 290; k = physconst('Boltzmann');```

Compute the noise power per unit bandwidth, split evenly between the in-phase and quadrature channels.

`Noise_power = 10*log10(k*T/2);`