A time varying magnetic field \$\vec{B}\$ induces an electric field \$\vec{E}_{induced}\$ which satisfies the equations

$$\nabla \cdot \vec{E}_{induced} = 0$$
$$\nabla \times \vec{E}_{induced} = \vec{B}$$

>Note: If a conductor is located within the electric field, the induced electric field will cause the electrons in the conductor to rearrange. This rearrangement will cause a _reaction_ electric field \$\vec{E}_{reaction}\$ to be created which satisfies the equations
>
>$$\nabla \cdot \vec{E}_{reaction} = \frac{\rho}{\epsilon_0}$$
>$$\nabla \times \vec{E}_{reaction} = 0$$
>
>The total electric field \$\vec{E}_{total}\$ is given by
>
>$$\vec{E}_{total} = \vec{E}_{induced} + \vec{E}_{reaction}$$

The EMF induced in a curve \$\gamma\$ which begins at point \$P_1\$ and ends at point \$P_2\$ is given by

$$\mathscr{E}_{induced}=\int_{\gamma} \vec{E}_{induced} \cdot d\vec{\ell}$$

In your diagram, there are _two_ paths between any two points. One path going clockwise around the circle, and the other path going counter-clockwise. Therefore, there is not _one_ EMF induced between two points in your diagram, but _two_, one for each path.

>So what is the emf between AC?

$$\mathscr{E}_{induced}=\int_{\gamma AC} \vec{E}_{induced} \cdot d\vec{\ell}$$

where \$\gamma AC\$ is either the clockwise or counter-clockwise path from A to C.

>is it different from the emf between AB?

Yes, the emf "between" A and B is

$$\mathscr{E}_{induced}=\int_{\gamma AB} \vec{E}_{induced} \cdot d\vec{\ell}$$

where \$\gamma AB\$ is either the clockwise or counter-clockwise path from A to B.