Light Reflection and Refraction Test - 44

Concave lenses always produce images that are upright, virtual, reduced in size, and located on the object's side of the lens.
Therefore, the image of an object formed by a concave lens is always virtual and diminished.

$$f=10cm , v=12cm , u=?$$

Answer is D.

Refractive index is the the ratio of the velocity of light in a vacuum to its velocity in a specified medium.
The refractive index of water with respect to air is 1.33. So, the refractive index of air with respect to water will be the reciprocal.
Therefore, refractive index of air with respect to water will be 1/1.33 = 0.75.
Hence, refractive index of air with respect to water will be 0.75.

When rays of light fall on a convex lens, then the lens refracts(the incident ray undergoes refraction twice before leaving the convex lens) the incident light rays and merges the light rays at one point. The point where all the light rays meet is called its focus. It converges the light rays to a point. So It is also called a converging lens.

$$\text{Magnification}=\dfrac{\text{Image  size}}{\text{Object  size}}$$

Answer is B.

The diagram below shows a light ray undergoing refraction as it passes from air into water. The incident ray is a ray (drawn perpendicular to the wavefronts) that shows the direction that light travels as it approaches the boundary. Similarly, the refracted ray is a ray (drawn perpendicular to the wavefronts) that shows the direction that light travels after it has crossed over the boundary. In the diagram, a normal line is drawn to the surface at the point of incidence. This line is always drawn perpendicular to the boundary. The angle that the incident ray makes with the normal line is referred to as the angle of incidence. Similarly, the angle that the refracted ray makes with the normal line is referred to as the angle of refraction.
The cause of refraction is a change in light speed; and wherever the light speed changes most, the refraction is greatest. The speed is related to the optical density of a material that is related to the index of refraction of a material. Air is the least dense material (lowest index of refraction value) and water is the denser material (largest index of refraction value). Thus, it would be reasonable that the most refraction occurs for the transmission of light across an air-water boundary.
Hence, the angle of refraction will be smaller than the angle of incidence.

Stars twinkle when we see them from the Earth's surface because we are viewing them through thick layers of turbulent (moving) air in the earth atmosphere.

Stars appear as tiny dots in the sky; as their light travels through the many layers of the Earth's atmosphere, the light of the star is bent (refracted) many times and in random directions (light is bent when it hits a change in density - like a pocket of cold air or hot air). This random refraction results in the star winking out (it looks as though the star moves a bit, and our eye interprets this as twinkling).

Option A is correct.

In a spherical mirror, the position of the object or image is always measured from the pole of the mirror.

Object distance, $$u = -15\ cm $$