The electric resistance of a particular wire of iron is R. If its length and radius are doubled, then:
 

Resistances n, each of r ohm, when connected in parallel give an equivalent resistance of R ohm. If these resistances were connected in series, the combination would have resistance in ohms, equal to:

1. $\frac{\mathrm{R}}{{\mathrm{n}}^2}$

2. R/n

3. nR

4. n² R 

When a wire of uniform cross-section a, length l, and resistance R is bent into a complete circle, the resistance between any two diametrically opposite points will be:

1. R/2

2. R/4

3. R/8

4. 4R