Optical Instruments

To solve the problem, we need to understand the reason why a convex lens is used in a microscope.

1. Basic Properties of a Convex Lens:
A convex lens, also known as a converging lens, can produce both real and virtual images depending on the position of the object. When used properly, it can magnify small objects.

2. Working of a Simple Microscope:
In a simple microscope (which uses a single convex lens), the object is placed between the optical center and the principal focus of the lens.
In this configuration, the lens forms a magnified, virtual, and erect image on the same side of the lens as the object.

3. Application in Microscopes:
This magnified virtual image helps in observing small details of objects that cannot be seen with the naked eye, which is why convex lenses are preferred in microscopes.

Final Answer:
The convex lens is used in the microscope because .

To solve the problem, we need to determine how an air bubble in water behaves optically.

1. Understanding the Refractive Index Difference:
Air has a lower refractive index than water. So when light travels from water (denser medium) into an air bubble (rarer medium), it diverges away from the normal.

2. Nature of Lens Behavior:
A diverging lens causes parallel rays of light to spread apart after passing through it. Since the air bubble causes light rays to diverge when they enter and exit due to the curved boundary and refractive index difference, it behaves like a diverging lens.

3. Conceptual Analogy:
Just like a concave lens diverges light in air, an air bubble in water also diverges light due to the surrounding denser medium (water).

Final Answer:
An air bubble in water behaves like a Diverging lens.