Who discovered the mutagenic effect of $X$-rays?

The point of intersection of tangents at the ends of the latus rectum of the parabola $y^2 = 4x$ is equal to

Two identical condensers $M$ and $N$ are connected in series with a battery. The space between the plates of $M$ is completely filled with a dielectric medium of dielectric constant $8$,and a copper plate of thickness $d/2$ is introduced between the plates of $N$ ($d$ is the distance between the plates). Then the potential differences across $M$ and $N$ are,respectively,in the ratio:

Evolutionary classification is called ........

Two planoconvex lenses each of focal length $10 \, cm$ and refractive index $3/2$ are placed as shown. In the space left, water $(R.I = 4/3)$ is filled. The whole arrangement is in air. The optical power of the system is (in diopters):

$A$ cubical block of wood with a side length of $10 \, cm$ floats at the interface between oil and water,with its lower surface horizontal and $4 \, cm$ below the interface. The density of oil is $0.6 \, g \cdot cm^{-3}$ and the density of water is $1 \, g \cdot cm^{-3}$. The mass of the block is ...... $gm$.