Question

A student took three concave mirrors of different focal lengths and performed the experiment to see the image formation by placing an object at different distance with these mirrors as shown in the following table. 

Case No.	Object-distance	Focal length
I	45 cm	20 cm
II	30 cm	15 cm
III	20 cm	30 cm

Now answer the following questions:

(a) List two properties of the image formed in Case I.

(b) In which one of the cases given in the table, the mirror will form real image of same size and why?

(c) Name the type of mirror used by dentists. Given reason why do they use such type of mirrors.

OR

(c) Look at the table and identify the situation (object distance and focal length) which resembles the situation in which concave mirrors are used as shaving mirrors? Draw a ray diagram to show the image formation in this case.

Answer 1

(a) In case (I), object is beyond C. For concave ‘mirrors, when the object is outside C, the image will be between C and F, and the image will be inverted and diminished (smaller than the object).

(b) In case (II), object is at C, so the image formed will be real and of same size.

(c) The dentist positions a small concave mirror so that the tooth is in focus. The dentist then examines a magnified image of the tooth in the concave mirror. Because the tooth seems considerably larger in the concave mirror, the dentist may easily check the tooth defect.

OR

(c) We are aware that a virtual and expanded picture is created when an object is positioned between P and F of a concave mirror. As a result, we can properly shave using a concave mirror because the microscopic hairs are easily visible.

In scenario (III), the object is positioned between F and P, simulating the use of concave mirrors as shaving mirrors.