A step down transformer has turns ratio 20:1. If 8V are applied across $0.4\ \Omega$ secondary then the primary current will be

A simple microscope is used to see the object first in blue light and then in red light. Due to the change from blue to red light, what is the effect on its magnifying power?

In Young's double slit experiment, the fringe width is 0.4 mm. What is the distance between $4^{\text{th}}$ dark band and $6^{\text{th}}$ bright band on the same side of the interference pattern?

The ratio of intensities at two points on the screen in Young's double slit experiment when waves from the two slits have a path difference of zero and $\lambda/4$ is ($\lambda$ is the wavelength of light used) ($\cos 0^\circ = 1$, $\cos\pi/2 = 0$)