Spherical Mirrors - Concave Mirror

A concave mirror is a type of spherical mirror where the inner curved surface is the reflecting surface. This mirror is shaped like the inside of a hollow sphere, allowing light to reflect from its inner surface. Concave mirrors are commonly used in applications such as telescopes, shaving mirrors, headlights, and solar devices, as they can focus light and form magnified or real images depending on the distance of the object from the mirror.

The formation of an image depends upon the position of the object. There are six possibilities for the position of the object in the case of a concave mirror.

1. Object at infinity
2. Object between infinity and centre of curvature (C)
3. Object at centre of curvature (C)
4. Object between centre of curvature (C) and Principal focus (F)
5. Object at Principal Focus (F)
6. Object between Principal Focus (F) and Pole (P)

1. Object at infinity:

Since parallel rays coming from the object converge at the principal focus, F, of a concave mirror after reflection. Hence, when the object is at infinity, the image will form at F.

• Point-sized
• Highly diminished
• Real and inverted

2. Object between infinity and the centre of curvature (C):

When an object is placed between infinity and the centre of curvature of a concave mirror, the image is formed between the centre of curvature (C) and the focus (F).

• Diminished compared to object
• Real and inverted

3. Object at Centre of Curvature (C):

When the object is placed at the centre of curvature (C) of a concave mirror, a real and inverted image is formed at the same position.

• Same size as object
• Real and inverted

4. Object between Centre of Curvature (C) and Principal Focus (F):

When the object is placed between the centre of curvature and the principal focus of the concave mirror, a real image is formed beyond the centre of curvature (C).

• Larger than object
• Real and inverted

• In barber shops and dental clinics, concave mirrors are used to create erect, virtual, and magnified images when objects are placed between the mirror’s pole and focus.
• In torches and vehicle headlights, the light source is placed at the focus, producing a parallel beam of light.
• For floodlights, the light source is positioned slightly beyond the mirror’s centre of curvature, resulting in a bright and focused beam.
• In solar devices, concave mirrors reflect sunlight to converge at the focal point, generating intense heat for solar furnaces or energy equipment.
• Concave mirrors are used as shaving mirrors to produce a larger, magnified image of the face for clear visibility during shaving.
• Dentists use concave mirrors to magnify the image of a tooth for better examination when the tooth is positioned between the focus and the pole.
• In solar furnaces, the concentrated sunlight reflected by the concave mirror generates extreme heat at the focal point, making it ideal for high-temperature applications.