SSC JE Electrical Engineering 2017 Set 3 Paper

When external field resistance is added in the field of DC shunt generator then resistance of field winding increase and field current (${\mathit{I}}_{\mathit{C}}$ ) reduce.
$\left[{\mathit{I}}_{\mathrm{f}}\propto \mathit{\varphi }\right]$
So flux is reduced when Emf is reduce $\left[\downarrow \mathit{E}\propto \mathit{\varphi }\downarrow \mathrm{w}\right]$ At constant mechanical power Input.
$\left[{\mathit{E}}_{\mathit{b}}\propto \mathrm{v}\right]$
Due to reduce in EMF, decrease voltage of generator.