Two identical square rods of metal are welded end to end as shown in figure $(a)$. $20 \text{ calories}$ of heat flows through them in $4 \text{ minutes}$. If the rods are welded as shown in figure $(b)$,the same amount of heat will flow through the rods in ...... $\text{min}$.

In the figure,the potentiometer wire $AB$ of length $L$ and resistance $9r$ is joined to the cell $D$ of $emf$ $\varepsilon$ and internal resistance $r$. The cell $C$'s $emf$ is $\varepsilon / 2$ and its internal resistance is $2r$. The galvanometer $G$ will show no deflection when the length $AJ$ is

$A$ piece of semiconductor is connected in series in an electric circuit. On increasing the temperature,the current in the circuit will

Assertion: The ferromagnetic substance does not obey Curie's law.
Reason: At Curie point, a ferromagnetic substance starts behaving as a paramagnetic substance.

The decreasing order of nucleophilicity among the following nucleophiles is:
$(I)$ $CH_3-COO^-$
$(II)$ $CH_3-O^-$
$(III)$ $CH_3-CH_2^-$
$(IV)$ $CH_3-SO_3^-$

$A$ uniform chain of length $L$ is lying on a horizontal table. If the coefficient of friction between the chain and the table top is $\mu$,what is the maximum length of the chain that can hang over the edge of the table without disturbing the rest of the chain on the table?