The anode voltage of a photocell is kept constant. The wavelength of the light incident on the cathode is changed gradually. Which of the following graphs represents the variation of the photoelectric current $(I)$ with the wavelength $(\lambda)$?

Consider the following statements: $(1)$ Both wave and particle nature are required for a complete understanding of light. $(2)$ Light cannot exhibit both wave and particle nature simultaneously in a single experiment.

Which of the following support the quantum nature of the $EM$ radiations?
$(A)$ Photoelectric effect
$(B)$ Compton effect
$(C)$ Doppler effect
$(D)$ Field effect

The radiation corresponding to the $3 \rightarrow 2$ transition of a hydrogen atom falls on a gold surface to generate photoelectrons. These electrons are passed through a magnetic field of $5 \times 10^{-4} \, T$. Assume that the radius of the largest circular path followed by these electrons is $7 \, mm$. The work function of the metal is $..... \, eV$. (Mass of electron $= 9.1 \times 10^{-31} \, kg$)

Name the device used for measuring the mass of atoms and molecules.

Give a powerful way to determine an upper limit to the size of the electron.