# The thermo e.m.f of a thermo-couple is given by , $\xi =a T +bT^2,$ where $a/b=-200^{\circ}C$. If the cold function is kept at $30^{\circ}$, then the inversion temperature is ($\xi$ in volts, T is in centigrade):

$\begin {array} {1 1} (1)\;103\;K & \quad (2)\;143\;K \\ (3)\;333\;K & \quad (4)\;443\;K \end {array}$

$(4)\;443\;K$