When an external resistance of $$5\,\Omega$$ is connected across terminals of a cell,  a current of $$0.25$$ A flow through it. When the $$5\,\Omega$$ resistor is replaced by a  $$2\,\Omega$$ resistor, a current of $$0.5$$ A flow through it. The internal resistance of the cell is________ $$\Omega$$.