$\frac{\Delta a }{ a } \times 100=1 \%,$$ \frac{\Delta b }{ b } \times 100=3 \%,$$ \frac{\Delta c }{ c } \times 100=2 \%$ and $\frac{\Delta d }{ d } \times 100=2 \%$
$\frac{\Delta A }{ A } \times 100=2 \frac{\Delta a }{ a } \times 100+3 \frac{\Delta b }{ b } \times 100+$$\frac{\Delta c }{ c } \times 100+\frac{1}{2} \times \frac{\Delta d }{ d } \times 100$
$\frac{\Delta A }{ A } \times 100=2 \times 2+3 \times 1+3+\frac{1}{2} \times 4=12 \%$
જયાં $B$ = ચુંબકીય ક્ષેત્ર, $l$ = લંબાઇ ,$m$ =દળ