Which of the following represents a $volt$?

The temperature at which thermo-emf is zero is

Two bulbs consume the same power when operated at $200\, V$ and $300\, V$ respectively. When these bulbs are connected in series across a $D.C.$ source of $500\, V$,then:

At time $t = 0$,terminal $A$ in the circuit shown in the figure is connected to $B$ by a key and alternating current $I(t) = I_0 \cos(\omega t)$,with $I_0 = 1 \text{ A}$ and $\omega = 500 \text{ rad s}^{-1}$ starts flowing in it with the initial direction shown in the figure.
At $t = \frac{7\pi}{6\omega}$,the key is switched from $B$ to $D$. Now onwards only $A$ and $D$ are connected. $A$ total charge $Q$ flows from the battery to charge the capacitor fully. If $C = 20 \mu\text{F}$,$R = 10 \Omega$ and the battery is ideal with emf of $50 \text{ V}$,identify the correct statement$(s)$.
$(A)$ Magnitude of the maximum charge on the capacitor before $t = \frac{7\pi}{6\omega}$ is $1 \times 10^{-3} \text{ C}$.
$(B)$ The current in the left part of the circuit just before $t = \frac{7\pi}{6\omega}$ is clockwise.
$(C)$ Immediately after $A$ is connected to $D$,the current in $R$ is $10 \text{ A}$.
$(D)$ $Q = 2 \times 10^{-3} \text{ C}$.

Which of the following circuits follows Ohm's law?

Two cables of copper are of equal lengths. One of them has a single wire of area of cross-section $A$, while the other has $10$ wires of cross-sectional area $A / 10$ each. Determine their suitability for transporting $A.C.$ and $D.C.$