Power (P) = 1/f = 1/(-0.15) = -6.67 D.

The focal length (f) of a concave mirror is half the radius of curvature (R). Therefore, f = R/2 = 20 cm / 2 = 10 cm.

Power (P) is given by P = 1/f (in meters). Thus, P = 1/0.15 = +6.67 D.

A negative focal length indicates that the lens is a concave lens.

A ray of light passing through the optical center of a lens continues in a straight line without bending.

When the angle of incidence equals the angle of refraction, it indicates that the light is passing from one medium to another of the same optical density, hence they are the same medium.

According to Snell's law, if the angle of incidence equals the angle of refraction, the light is traveling in the same medium, which can be vacuum or air.

Concave lenses always produce virtual and erect images regardless of the object distance.

The radius of curvature (R) is twice the focal length (f). Therefore, R = 2f = 2 * 10 cm = 20 cm.

The radius of curvature (R) is twice the focal length (f). Therefore, R = 2f = 2 * 20 cm = 40 cm.

Power (P) = 1/f (in meters). Here, f = 0.2 m, so P = 1/0.2 = +5 D.

Power (P) is given by P = 1/f (in meters). Thus, P = 1/0.25 m = +4 D.

The focal length f of a mirror is given by f = R/2. Thus, f = 40 cm / 2 = 20 cm.

The focal length (f) of a spherical mirror is given by f = R/2. Here, R = 40 cm, so f = 40/2 = 20 cm.

The speed of light in a medium is given by v = c/n. Here, c = 3 x 10^8 m/s and n = 1.5, so v = 3 x 10^8 / 1.5 = 2 x 10^8 m/s.

Magnification (m) is given by m = -v/u. Here, m = -10/15 = -2/3, which means the magnification is 1.5 in absolute value.

The critical angle for water to air is approximately 48.6 degrees. Therefore, the minimum angle of incidence is 60 degrees.

When a lens is immersed in a medium with a higher refractive index, its effective focal length decreases due to the reduced refractive power.

When an object is placed at infinity, a concave lens forms a virtual image at its focal point, which is upright.

When the object is at the center of curvature, the image formed is real, inverted, and of the same size.

When the object is placed between the focal point and the mirror, the image formed is virtual and upright.

When the object is within the focal length of a convex lens, the image formed is virtual.

The speed of light decreases when it passes from a less dense medium (air) to a denser medium (glass) due to the change in refractive index.

Critical angle (C) is given by sin(C) = n2/n1. Thus, sin(C) = 1/1.5, C = sin^(-1)(0.6667) ≈ 41.8 degrees.

The critical angle (θc) can be calculated using sin(θc) = n2/n1. Thus, sin(θc) = 1/1.33, giving θc ≈ 53.1 degrees.

The critical angle (θc) can be calculated using sin(θc) = 1/n. Here, n = 1.5, so θc = sin^(-1)(1/1.5) ≈ 41.81 degrees, which is approximately 42 degrees.

The critical angle θc is given by sin(θc) = n2/n1. Thus, θc = sin^(-1)(1/1.5) ≈ 41.8 degrees.

The critical angle (θc) can be calculated using sin(θc) = n2/n1. Here, n1 = 1.33 (water) and n2 = 1 (air). Thus, sin(θc) = 1/1.33, giving θc ≈ 53.1 degrees.

Using the mirror formula, 1/f = 1/v + 1/u. Here, v = -15 cm (real image) and u = -30 cm (object distance). Thus, 1/f = 1/(-15) + 1/(-30) = -1/10, so f = -10 cm.

Using the mirror formula 1/f = 1/v + 1/u, where u = -30 cm and v = -10 cm, we find f = 15 cm.