Question

Two circular coils have diameters 10cm and 20cm with same number of turns. The ratio 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)

$B =\frac{ n }{ r }$
$\frac{ B _{1}}{ B _{2}}=\frac{\frac{ n _{1}}{ r _{1}}}{\frac{ n _{2}}{ r _{2}}}$
$\frac{ B _{1}}{ B _{2}}=\frac{ n _{1} r _{2}}{ n _{2} r _{1}}$
$=\frac{1 \times 20}{1 \times 10}$
$=2: 1$