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# Threshold wavelength for photoelectric emission from a metal surface is 5200 $A^{\circ}$ will be emitted when this surface is illuminated with monochromatic radiation from . Photoelectrons

$\begin {array} {1 1} (a)\;1W\: IR\: lamp & \quad (b)\;50\: W\: UV\: lamp \\ (c)\;50\: W \: IR \: lamp & \quad (d)\;10 \: W\: IR\: lamp \end {array}$

threshold value which is 5200 $A^{\circ}$
wavelength of IR light = 7800 $A^{\circ}$
wavelength of UV light = 4000 $A^{\circ}$