Electrons ar emitted with zero velocity from a metal surface when it is exposed to radiation of wavelength `6800 A^(@).` Calculate threshold frequency `(v _(0))` and work function (w) of the metal.

Explanation

We know that
`K.E.= hv - hv _(0)`
If the velocity of zero, K.E. = 0
`therefore 0 = hv - hv _(0)`
`or h v = hv _(0)`
`or v = v _(0)`
`therefore v = (c)/( lamda ) = ( 3. 0 xx 10 ^(8) ms ^(-1) )/( 8600 xx 10 ^(-10) m ) = 4.41 xx 10 ^(14) s ^(-1)`
Threshold frequency`=4.41 xx 10^(14) s ^(-1)`
Work function `= hv_(0) = 6.626 xx 10 ^(-34) xx 4.4 1 xx 10^(14) = 2. 92 xx 10 ^(-19) J`