What is meant by saying that the potential difference between two points is $1$ $V$?

Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be -

Let the resistance of an electrical component remain constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?

Define the unit of electric current.

An electric lamp of $100 \,\Omega$,a toaster of resistance $50 \,\Omega$,and a water filter of resistance $500 \,\Omega$ are connected in parallel to a $220 \,V$ source. What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances,and what is the current through it?

$A$ copper wire has a diameter of $0.5\, mm$ and a resistivity of $1.6 \times 10^{-8}\, \Omega \, m$. What will be the length of this wire to make its resistance $10\, \Omega$? How much does the resistance change if the diameter is doubled?