What is the glancing angle if the angle of incidence is 35^?

The angle of incidence is the angle between the incident ray and the normal to the surface.
The glancing angle (or grazing angle) is the angle between the incident ray and the surface itself.

The normal is perpendicular to the surface, so the angle between the normal and the surface is $90^\circ$.
Therefore, the glancing angle and the angle of incidence are complementary.

The correct option is B.
The final answer is $\boxed{\text{B. } 55^\circ}$.

The principle of reversibility of light states that if a ray of light, after suffering any number of reflections or refractions, has its path reversed, it will retrace its original path.

• A. Light always travels in straight lines: This is a property of light propagation, not the principle of reversibility.
• B. If light travels from point A to point B along a certain path, it will travel from point B to point A along the same path if its direction is reversed: This accurately describes the principle of reversibility.
• C. Light cannot be reflected or refracted: This is incorrect; light undergoes reflection and refraction.
• D. Light always travels at the same speed: This is incorrect; light speed changes in different media.

The correct option is B.
The final answer is $\boxed{\text{B. If light travels from point A to point B along a certain path, it will travel from point B to point A along the same path if its direction is reversed}}$.

For a concave mirror, when an object is placed at the centre of curvature (C), the image is formed at the centre of curvature (C) as well.

The image formed is real, inverted, and has the same size as the object.

• A. Virtual, upright, magnified: Incorrect.
• B. Real, inverted, same size as object: Correct.
• C. Real, upright, diminished: Incorrect (real images are inverted).
• D. Virtual, inverted, magnified: Incorrect (virtual images are upright).

The correct option is B.
The final answer is $\boxed{\text{B. Real, inverted, same size as object}}$.

• When the object is far away (beyond C), the image is real, inverted, and diminished, formed between F and C.
• As the object moves from C towards F, the image moves from C towards infinity, becoming real, inverted, and magnified.
• When the object is at F, the image is formed at infinity.
• When the object is between F and P, the image is formed behind the mirror, becoming virtual, upright, and magnified.