Question

If the current in the circuit for heating the filament is increased, the cutoff wavelength
(a) will increase
(b) will decrease
(c) will remain unchanged
(d) will change

Answer 1

(c) will remain unchanged

Cut off wavelength is given by
${\lambda }_{\min }=\frac{hc}{eV}$,
where h = Planck's constant
c = speed of light
e = charge on an electron
V = potential difference applied to the tube
Clearly, the cutoff wavelength does not depend on the current in the circuit and temperature of the filament.