In Young's double slit experiment, the distance between the slits is 2 mm and the slits are 1 m away, from the screen. Two interference patterns can be obtained on the screen due to light of wavelength ' $\lambda_1$ ' and ' $\lambda_2$ ' respectively. The separation on the screen between the $3^{\text {rd }}$ order bright fringes on the two interference patterns is ( $\lambda_2=1.5 \lambda_1$ )

$\mathrm{L}, \mathrm{C}$ and R are connected in series to an a. c. source. Which one of the following is true?

Phase relation between current and voltage is such that

A bar of iron having magnetic moment $2.4 \mathrm{Am}^2$ weighs 66 g . If the density of the material of the bar is $7700 \mathrm{~kg} / \mathrm{m}^3$, the intensity of magnetisation in $\mathrm{Am}^{-1}$ is

The error in the measurement of length and mass is $3 \%$ and $4 \%$ respectively. The error in the measurement of density will be