(a(i))[1]
From Fig. 7.1, calculate the clockwise moment produced by the weight of the wooden arm about the pivot.
(a(ii))[3]
Calculate the distance $d$ between the pivot and the joint holding the soft iron bar A.
(b(i))[3]
State and explain what happens to the wooden barrier arm when the switch in the coil circuit is closed.
(b(ii))[2]
State and explain how the effect on the wooden barrier arm compares with the effect in (b)(i).
(b(iii))[2]
Explain why a steel bar is less suitable than a soft iron bar in the barrier.