The solids which have the negative temperature coefficient of resistance are:

$A$ metal rod of length $10 \text{ cm}$ and a rectangular cross-section of $1 \text{ cm} \times 0.5 \text{ cm}$ is connected to a battery across opposite faces. The resistance will be . . . . . . .

Two wires are made of two different materials whose specific resistances are in the ratio $2:3$,lengths are in the ratio $3:4$,and cross-sectional areas are in the ratio $4:5$. The ratio of their resistances is:

Three copper wires of lengths and cross-sectional areas are $(l, A)$,$(2l, A/2)$,and $(l/2, 2A)$. Resistance is minimum in

The resistance of a wire at $30^{\circ}C$ is $10\, \Omega$. To increase the resistance of the wire by $10\%$,the temperature should be .......... $^{\circ}C$. The temperature coefficient of resistance of the material of the wire is $0.002\, ^{\circ}C^{-1}$.

The resistance of a tungsten wire at $150^{\circ} C$ is $133 \Omega$. The temperature coefficient of resistance is $0.0045^{\circ} C^{-1}$. The resistance of this wire at $500^{\circ} C$ is: (in $Omega$)