SSC JE Electrical Engineering 2017 Set 3 Paper

If supply voltage in DC shunt motor is reverse.then both armature current (${\mathit{I}}_{\mathit{a}}$) and field current ${\mathit{I}}_{\mathrm{sn}}$ both reverse.
$\left[\mathit{T}\propto \mathit{\varphi }{\mathit{I}}_{\mathit{a}}\right]$
due to both flux and armature current reverse.
No effect in torque direction.