$A$ and $B$ are two square plates of the same metal and same thickness,but the length of $B$ is twice that of $A$. The ratio of the resistances of $A$ and $B$ is

The resistance of the filament of an 'incandescent' bulb increases with an increase in temperature. If $R_{100}$,$R_{60}$,and $R_{40}$ are the resistances of $100 \ W$,$60 \ W$,and $40 \ W$ bulbs at room temperature,respectively,then:

$n$ conducting wires of same dimensions but having resistivities $1, 2, 3, . . . , n$ are connected in series. The equivalent resistivity of the combination is

The masses of three wires of copper are in the ratio of $1 : 3 : 5$ and their lengths are in the ratio $5 : 3 : 1.$ The ratio of their electrical resistances is

The resistance of a conductor at $15^{\circ}C$ is $16\, \Omega$ and at $100^{\circ}C$ is $20\, \Omega$. What will be the temperature coefficient of resistance of the conductor?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A:$ Alloys such as constantan and manganin are used in making standard resistance coils.
Reason $R:$ Constantan and manganin have a very small value of temperature coefficient of resistance.
In the light of the above statements, choose the correct answer from the options given below.