The schematic symbol of a light emitting diode $(LED)$ is:

With increasing biasing voltage of a photodiode,the photocurrent magnitude

The device that can detect optical signals is

To measure light intensity,we use:

$A$ light emitting diode $(LED)$ is fabricated using $GaAs$ semiconducting material whose band gap is $1.42 \,eV$. The wavelength of light emitted from the $LED$ is: (in $\,nm$)

$A$ light emitting diode $(LED)$ has a voltage drop of $2\,V$ across it and passes a current of $10\,mA$ when it operates with a $6\,V$ battery through a limiting resistor $R$. The value of $R$ is $......\,k\Omega$.