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# Light

## 04 Image Formation and Uses of Spherical Mirrors

#### 4.1 IMAGE FORMED BY CONCAVE MIRROR IN DIFFERENT POSITIONS:

(I)Object placed between pole and focus of the mirror i.e. P and F

Here, the image formed is:

(i) behind the mirror,
(ii) virtual and erect, and
(iii) larger than the object (or magnified)

(II)Object placed at the focus of a concave mirror i.e. object is at F

Here, the image formed is:

(i) at infinity,
(ii) real and inverted, and
(iii) highly magnified (or highly enlarged).

(III)Object placed between focus and centre of curvature i.e. Object between F and C

The image formed is:

(i) beyond the centre of curvature,
(ii) real and inverted, and
(iii) larger than the object (or magnified).

(IV)Object placed at the centre of curvature of a concave mirror (Object at C)

Here, image formed is:

(i) at the centre of curvature (C) ,
(ii) real and inverted, and
(iii) same size as the object.

(V)Object placed beyond the centre of curvature (Object beyond C)

The image formed is:

(i) between the focus and centre of curvature,
(ii) real and inverted, and
(iii) smaller than the object (or diminished).

(VI) Object placed at infinity

The image formed is:

(i) at the focus (F)
(ii) real and inverted, and
(iii) much smaller than the object (or highly diminished).

Summary of the Images Formed by a Concave Mirror

Position of object Position of image Size of image Nature of image
1. Within focus (between pole P

and focus F)

Behind the mirror Enlarged Virtual and erect
2. At focus (F) At infinity Highly enlarged Real and inverted
3. Between F and C Beyond C Enlarged Real and inverted
4. At C At C Equal to object Real and inverted
5. Beyond C Between F and C Diminished Real and inverted
6. At infinity At focus (F) Highly diminished Real and inverted

#### 4.2 USES OF CONCAVE MIRRORS

(i) Used in shaving mirrors for seeing a larger image of the face. This helps in making smooth shave, as when the face is held within the focus of a concave mirror, then an enlarged image of the

(ii) Used by dentists to see the large images of the teeth of patients.

(iii) Concave mirrors are used as reflectors in torches, vehicle head-light and search lights to get powerful beams of light. This is because when a lighted bulb is placed at the focus of a concave reflector, then the concave reflector produces a powerful beam of parallel light rays. This helps us see things up to a considerable distance in the darkness of night.

(iv) Concave mirrors are used as doctor’s head-mirrors to focus light coming from a lamp on to the body parts of a patient (such as eye, ear, nose, throat, etc.) to be examined by the doctor.

(v) Large concave mirrors are used in the field of solar energy to focus sun’s rays for heating solar furnaces.

(vi)Concave dishes are used in TV dish antennas to receive TV signals from the distant communications satellites.Such signals are weak as they travel a long distance and need to be amplified. Many such signals strike the concave mirror as parallel rays and get concentrated at the focal point of the mirror.

#### 4.3 FORMATION OF IMAGE BY A CONVEX MIRROR

A convex mirror always produces an erect (right side up) image of the objects.
The image formed in a convex mirror is highly diminished or much smaller than the object, due to which a convex mirror gives a wide field of view.

(I)When the object is placed at infinity:

Here the image is :
(i) formedbehind the mirror at the principal focus
(ii) highly diminished,
(iii) virtual and erect

(II)Oject placed between pole and infinity:

Here the image is :
(i) formed behind the mirror, between the pole and the principal focus
(ii) diminished
(iii) Virtual and erect

Summary of the Images Formed by a Convex Mirror

Position of object Position of image Size of image Nature of image
1. Between infinity and the pole P Between P and F, behind the mirror Diminished Virtual and erect
6. At infinity At the focus F, behind the mirror Highly diminished Virtual and erect

#### 4.4 USES OF CONVEX MIRRORS

1. Rear-View Mirrors in vehicles: Convex mirrors are used as rear-view mirrors in vehicles (like cars, trucks and buses) to see the traffic at the rear side (or back side)

2. Security mirrors in ATM: Security mirrors are kept near the ATM’s so that the bank customer can check that somebody is behind them or not.

#### Lens Formula, Magnification and Power of Lens

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