A lamp is rated at $240 \mathrm{~V}, 60 \mathrm{~W}$. When in use the resistance of the filament of the lamp is 20 times that of cold filament. The resistance of the lamp when not in use is

A straight wire of resistance $R$ is bent in the shape of $f_d$ square. A cell of emf 12 V is connected between two adjacent corners of the square. The potential difference across any diagonal of the square is

In the given circuit, if the potential at point $B$ is 24 V , the potential at point $A$ is

A block has dimensions $1 \mathrm{~cm}, 2 \mathrm{~cm}$ and 3 cm . Ratio of the maximum resistance to minimum resistance between any palr of opposite faces of the block is