In Young's double slit experiment, the two slits are 'd' distance apart. Interference pattern is observed on a screen at a distance 'D' from the slits. A dark fringe is observed on a screen directly opposite to one of the slits. The wavelength of light is

A black body radiates maximum energy at wavelength '$$\lambda$$' and its emissive power is 'E' Now due to change in temperature of that body, it radiates maximum energy at wavelength $$\frac{2 \lambda}{3}$$. At that temperature emissive power is

In meter bridge experiment, null point was obtained at a distance '$$l$$' from left end. The values of resistances in the left and right gap are doubled and then interchanged. The new position of the null point is

The magnetic field at the centre of a circular coil of radius '$$R$$', carrying current $$2 A$$ is '$$B_1$$'. The magnetic field at the centre of another coil of radius '$$3 R$$' carrying current $$4 A$$ is '$$B_2$$'. The ratio $$B_1:B_2$$ is