A $$dc$$ series motor is rated $$230V,$$ $$1000$$ $$rpm,$$ $$80$$ $$A$$ (refer to Figure). The series field resistance is $$0.11\,\Omega ,$$ and the armature resistance is $$0.14\,\Omega .$$ If the flux at an armature current of $$20A$$ is $$0.4$$ times of that under rated condition, calculate the speed at this reduced armature current of $$20$$ $$A.$$

An ideal transformer has a linear $$B-H$$ characteristic with a finite slope and a turns ratio of $$1:1.$$ The primary of the transformer is energized with an ideal current source, producing the signal i as shown in figure. Sketch the shape (neglecting the scale factor) of the following signals, labeling the time axis clearly

$$(a)$$ $$\,\,\,\,\,$$ the core flux $${\phi _{oc}}$$ with the secondary of the transformer open
$$(b)$$ $$\,\,\,\,\,$$ the open-circuited secondary terminal voltage $${V_2}\left( t \right).$$
$$(c)$$ $$\,\,\,\,\,$$ the short-circuited secondary current $${i_2}\left( t \right)$$
$$(d)$$ $$\,\,\,\,\,$$ the core flux $${\phi _{sc}},$$ with the secondary of the transformer short-circuited.

The electric field $$\overrightarrow E $$ (in volts/metre) at the point $$(1, 1, 0)$$ due to a point charge of $$+1$$ $$\mu C$$ located at $$\left( { - 1,\,1,\,1} \right)$$ (coordinates in metres) is

Given the potential function in free space to be $$V\left( x \right) = \left( {50{x^2} + 50{y^2} + 50{z^2}} \right)$$ volts, the magnitude (in volts /metre) and the direction of the electric field at a point $$\left( {1,\,\, - 1,\,\,1} \right),$$ where the dimensions are in metres, are