A lens of refractive index '$\mu$' has focal length '$f$'. When the lens is immersed in a liquid of refractive index '$\mu_0$', its focal length becomes '$f_0$'. Then '$f_0$' is given by

In Young's double slit experiment, width of the second slit is double the width of first slit, consequently the amplitude of the light from two slits. '$I_m$' is the maximum intensity. The resultant intensity '$I$' when they interfere with the phase difference of $\phi$ is given by

In a single slit diffraction experiment, for wavelength '$\lambda$', half angular width of the principal maxima is '$\theta$'. Also for wavelength of light '$p\lambda$', the half angular width of the principal maxima is '$q\theta$'. The ratio of the half angular widths of the first secondary maxima in the first case to second case will be

Photoelectric emission is observed from a metallic surface for frequencies $\nu_1$ and $\nu_2$ of the incident light rays ($\nu_1 > \nu_2$). If the ratio of maximum value of kinetic energy of the photoelectron emitted in first case to that in second case 3 : K, then the threshold frequency of the metallic surface is