A voltmeter of resistance $400 \Omega$ is used to measure the emf of a cell with an internal resistance of $4 \Omega$. The error in the measurement of emf of the cell is

When two wires are connected in the two gaps of a meter bridge, the balancing length is 50 cm . When the wire in the right gap is stretched to double its lengt ${ }^{-}$ and again connected in the same gap, then the new balancing length from the left. end of the bridge wiu :

The resistance of a wire is $2.5 \Omega$ at a temperature 373 K . If the temperature coeffficient of resistance of the material of the wire is $3.6 \times 10^{-3} \mathrm{~K}^{-1}$, its resistance at a temperatrue 273 K is nearly.