1) Light of wavelength λph falls on a cathode plate inside a vacuum tube as shown in the figure. The work function of the cathode surface is Φ and the anode is a wire mesh of conducting material kept at a distance d from the cathode. A potential difference V is maintained between the electrodes. If the minimum de-Broglie wavelength of the electrons passing through the anode is λe . which of the following statement (s) is (are) true ? A) λe increases at the same rate as λph for λph < hcϕ B) λe is approximately halved, if d is doubled C) λe decreases with increase in ϕ and o λph D) For large potential difference (V≫ϕ/e),λe is approximately halved if V is made four times Answer: Option DExplanation:kmax=hcλph−ϕ Kinetic energy of electron reaching the anode will be K=hcλph−ϕ+eV Now λe=h√2mK =h√2m(hCλph−ϕ+eV) If eV>>Φ λe=h√2m(hCλph+eV) If Vf=4Vi,(λe)f≈(λe)i