What is the resistance of an electric arc lamp,if the lamp uses $20\, A$ when connected to a $220\, V$ line?

Why are alloys commonly used in electrical heating devices?

$(a)$ For the circuit shown in the diagram,calculate:
$(i)$ The value of current through the $30\, \Omega$ resistor.
$(ii)$ The total resistance of the circuit.
$(b)$ Give two advantages of connecting electrical devices in parallel with a battery.

$(a)$ Name an instrument that measures potential difference between two points in a circuit. Define the unit of potential difference in terms of $SI$ unit of charge and work. Draw the circuit symbols for $(i)$ variable resistor,$(ii)$ a plug key which is closed.
$(b)$ Two electric circuits $(I)$ and $(II)$ are shown below.
$(i)$ Which of the two circuits has more resistance?
$(ii)$ Through which circuit does more current pass?
$(iii)$ In which circuit is the potential difference across each resistor equal?
$(iv)$ If $R_{1} > R_{2} > R_{3}$,in which circuit will more heat be produced in $R_{1}$ as compared to the other two resistors?

Derive the relation $R = R_{1} + R_{2} + R_{3}$ when three resistors $R_{1}, R_{2}$ and $R_{3}$ are connected in series in an electric circuit.

In the process of electroplating a chromium coating onto an iron spoon,where should the chromium rod be connected?