Measuring e.m.f. and Internal Resistance - Linear Graph

The Linear Graph

From the equation,

E = V + Ir

Therefore

V = -rI + E

Y axis = Potential difference (V)
X axis = Current (I)
Gradient od the grapf, m = - internal resistance (r)
Y intercept of the graph, c = e.m.f.

Example:

The graph shows the variation of potential difference with current of a battery.
What is the internal resistance and e.m.f. of the battery?

Answer:
e.m.f. = y-intercept = 3V

internal resistance,
r = -gradient of the graph
$$r=-\frac{-3}{6}=0.5\Omega$$