An aluminium wire is stretched to make its length $0.4 \%$ larger. Then the percentage change in resistance is $.....\,\%$.

At room temperature $(27^\circ \text{C})$ the resistance of a heating element is $100 \ \Omega$. What is the temperature of the element if the resistance is found to be $137 \ \Omega$,given that the temperature coefficient of the material of the resistor is $1.35 \times 10^{-4} \ ^\circ \text{C}^{-1}$ (in $^\circ \text{C}$)?

$A$ $100 \ W$ tungsten light bulb has a resistance of $250 \ \Omega$ when it is turned $ON$ and $25 \ \Omega$ when turned $OFF$. The ambient room temperature is $25^{\circ} C$. Find the temperature of the filament when the bulb is turned $ON$. (Let $\alpha_{\text{tungsten}} = 4.5 \times 10^{-3} /^{\circ} C$) (in $^{\circ} C$)

The new resistance of a wire of $R \, \Omega$,whose radius is reduced to half,is

The length of a given cylindrical wire is increased by $100\,\%$. Due to the consequent decrease in diameter,the percentage change in the resistance of the wire will be ................ $\%$.

The unit of specific resistance is