Opamp exam problem 2

Figure 1

2. What is the effect of a 5 mV input offset voltage on the output of the circuit shown in Figure 1?

Answer

Vos = 17.5 mV

When the opamp input voltage is zero, there will still be an outout voltage due to missmatching of components and lack of circuit symetry. The input offset voltage is this output voltage refered to the input.
Although the input is grounded, the input offset voltage appears like a voltage source connected to the non-inverting input, as shown in Figure 2. The output voltage is,
V_o = [1 + R₂/R₁]*V_os

Figure 2