Myu 1 and myu 2 are the refractive indexes . ,.,.,.,.,.,,.
if myu 1 = myu 2 then the focal length of lense will be infinite

**Introduction**

When a convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens, the behavior of light passing through the lens is affected. In this scenario, the focal length of the lens will be influenced. Let's discuss the possible outcomes and determine the correct answer.

**Explanation**

1. **Becoming Infinite**
- When a convex lens is dipped in a liquid with the same refractive index, the lens and the liquid become optically indistinguishable.
- In this case, the lens and the liquid effectively form a single medium with a uniform refractive index.
- The principle of refraction states that when light travels from a medium with a higher refractive index to a medium with a lower refractive index, it bends away from the normal.
- However, when the refractive indices of the lens and the liquid are equal, there is no difference in refractive index between the two media, and light does not undergo any bending at the lens interface.
- As a result, the lens loses its ability to converge or diverge light, and its focal length becomes infinite.

2. **Becoming Small, but Non-zero**
- When a convex lens is dipped in a liquid with a refractive index equal to its own, the lens and the liquid behave as a single medium, but there is still a change in the effective refractive index of the system.
- The effective refractive index of the system is given by the average of the refractive index of the lens and the refractive index of the liquid, weighted by their respective volumes.
- Due to this change in the effective refractive index, the focal length of the lens will also change.
- However, since the lens and the liquid have the same refractive index, the change in the effective refractive index will be minimal. Hence, the change in focal length will also be small but non-zero.

3. **Remaining Unchanged**
- This option is incorrect because a change in the refractive index of the medium surrounding the lens will always have an effect on the focal length of the lens.

4. **Becoming Zero**
- This option is also incorrect because when the refractive index of the lens and the liquid are equal, the lens and the liquid behave as a single medium and still have a finite focal length, as explained in option 2.

**Conclusion**

When a convex lens is dipped in a liquid with the same refractive index as the lens, its focal length will become small, but non-zero. This is because the effective refractive index of the lens-liquid system changes slightly, causing a small change in the focal length of the lens.