On which of the following factors does the resistance of a conductor depend?

$(a)$ What is the total resistance of $n$ resistors each of resistance $R$ connected in:
$(i)$ series?
$(ii)$ parallel?
$(b)$ Calculate the resultant resistance of $3$ resistors $3 \ \Omega, 4 \ \Omega$,and $12 \ \Omega$ connected in parallel.

What is the device (meter) used to measure electric potential difference called?

What is the practical unit used for electrical energy?

What is the unit of resistance?

$(a)$ 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.