The maximum resistance which can be made using four resistors each of resistance $\frac {1}{2}$W is(a) 2 W (b) 1 W (c) 2.5 W (d) 8 W

It is calculated as $\frac{1}{{R}_{T}}=\frac{1}{{R}_{1}}+\frac{1}{{R}_{2}}+\frac{1}{{R}_{3}}+\frac{1}{{R}_{4}}+........+\frac{1}{Rn}$

While total resistance increases when resistors are connected in series.

It is calculated as ${R}_{T}={R}_{1}+{R}_{2}+{R}_{3}+{R}_{4}+........+{R}_{n}$

It means, we can get minimum resistance, when all the given resistors will join in parallel, and maximum resistance can be obtained when all the given resistors will join in series.

So, for finding maximum resistance, we have to join all resistors in series.

Here, given 4 resistors each of resistance $\frac{1}{2}\Omega $ or $0.5\Omega $.

Now, putting the value of the resistors in the formula of series connection-

${R}_{T}= 0.5 + 0.5 + 0.5 + 0.5 $

${R}_{T}= 2\Omega $

Hence, maximum resistance, which can be made using four resistors each of $\frac{1}{2}\Omega $ is $2\Omega $.