State $Ohm's$ law. Calculate the resistance of a conductor,if the current flowing through it is $0.2 \, A$ when the applied potential difference is $0.8 \, V$.

Given below is a circuit showing current flowing in it. Identify each component $A, B, C, D$ of this circuit.

$(a)$ What do the following symbols represent in a circuit? Write the name and one function of each.
$(b)$ Draw a schematic diagram of a circuit consisting of a battery of $12 \, V$,three resistors of $5 \, \Omega$,$10 \, \Omega$,and $20 \, \Omega$ connected in parallel,an ammeter to measure the total current through the circuit,and a voltmeter to measure the potential difference across the combination of resistors.
$(c)$ State any one advantage of connecting electrical devices in parallel with the mains instead of connecting them in series in a household circuit.

State Ohm's law. How can it be verified experimentally? Does it hold good under all conditions? Comment.

Why is very less heat generated in long electric cables than in filaments of electric bulbs?

The resistance of a conducting wire is $10\, \Omega$. If a battery of $1.5\, V$ is connected to it,then how much electric current will flow through it (in $, mA$)?