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# 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$1.38\text{x}{10}^{-23}$ J/K. Most commonly denoted by k.

## 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);`