For gold plating on a copper chain,the substance required in the form of solution is

The thermo emf of a thermocouple is given by $E = aT + bT^2$,where $\frac{a}{b} = -200^{\circ}C$. If the cold junction is kept at $30^{\circ}C$,then the inversion temperature is ($\varepsilon$ in volt,$T$ in centigrade). (in $K$)

Consider the following two statements $A$ and $B$,and identify the correct choice out of the given answers:
$A$. Thermo $e.m.f.$ is minimum at the neutral temperature of a thermocouple.
$B$. When two junctions made of two different metallic wires are maintained at different temperatures,an electric current is generated in the circuit.

In the circuit diagram shown in the figure below, the current flowing through the resistance $3\, \Omega$ is $\frac{x}{3}\, A$. The value of $x$ is $...........$

In the following circuit,a bulb is rated as $1.5\, V$,$0.45\, W$. If the bulb glows with full intensity,then what will be the equivalent resistance between $X$ and $Y$? ............. $\Omega$

First,a set of $n$ equal resistors of $10 \; \Omega$ each are connected in series to a battery of emf $20 \; V$ and internal resistance $10 \; \Omega$. $A$ current $I$ is observed to flow. Then,the $n$ resistors are connected in parallel to the same battery. It is observed that the current is increased $20$ times. The value of $n$ is .... .