A current carrying toroid winding is internally filled with lithium having susceptibility \( \chi = 2.1 \times 10^{-5} \). What is the percentage increase in the magnetic field in the presence of lithium over that without it?
A circular coil of wire is made up of 200 turns, each of radius 10 cm. If a current of 0.5A passes through it, what will be the magnetic field at the centre of the coil?
Match List-I with List-II
\[\begin{array}{|l|l|} \hline \text{List I Content of humus} & \text{List II Percentage of contents} \\ \hline \text{(A) Carbon} & \text{(I) 35-40\%} \\ \hline \text{(B) Oxygen} & \text{(II) ~5\%} \\ \hline \text{(C) Hydrogen} & \text{(III) 55-60\%} \\ \hline \text{(D) Nitrogen} & \text{(IV) 15\%} \\ \hline \end{array}\]
Choose the correct answer from the options given below: