Question

Two circular coils have diameters $10cm$ and $20cm$ with same number of turns. The ratio of the magnetic field induction produced at the centre of the coils when connected in series is

• A. $1:2$
• B. $2:1$
• C. $4:1$
• D. $1:4$

Answer 1

Answer: (B)

$2:1$

$B=\frac{n}{r}$

$\frac{B_1}{B_2}=\frac{\frac{n_1}{r_1}}{\frac{n_2}{r_2}}$

$\frac{B_1}{B_2}=\frac{n_1{r}_2}{n_2{r}_1}$

$=\frac{1\times 20}{1\times 10}$

$=2:1$