A student wants to project the image of a candle flame on a screen 60 cm in front of a mirror by keeping the flame at a distance of 15 cm from its pole.
(a) Suggest the type of mirror he should use:
(i) convex mirror
(ii) plane mirror
(iii) concave mirror
(iv) none of the above
Since the student wants image on a screen , it has to be a real image
Now, let’s check both mirrors
- Convex mirrors always produce virtual images . It cannot be used to produce images on the screen.
- Concave mirrors produce real images on the screen in all cases except when the object is between pole and focus , therefore students should use a concave mirror because it forms real images.
- Plane mirrors always form virtual images. So, it cannot be used
So, the correct answer is (iii) Concave mirror
(b) Find the linear magnification of the image produced.
(i) – 4
(ii) + 4
(iii) – 900
(iv) + 900
So, the correct answer is (i) – 4
(c) When object distance is less than focal length the image is _______ and when object distance is more than focal length the image is ______.
(i) real, real
(ii) virtual. Virtual
(iii) real, virtual
(iv) virtual, real
In a concave mirror
- When object is kept between Focus and Pole , image formed is virtual
- When object is kept beyond focus (between C and F, at C and beyond C), image formed is real
So, the correct answer is (iv) virtual, real
(d) Draw a ray diagram for the given scenario.
(e) What is the distance between the object and its image?
(i) 15 cm
(ii) 45 cm
(iii) 75 cm
(iv) 0 cm
Object distance, u = -15cm
Image distance, v = -60cm
Distance between object and image = u - v
= -15 - (-60)
The correct answer is (ii) 15 cm
(e) The image formed in the above case is:
(i) virtual, inverted and magnified.
(ii) real, erect and magnified
(iii) real, inverted and magnified
(iv) real, erect and diminished
- Since the image is formed on a screen , it is real .
Also, we calculated the magnification of the image as m= -4.
- Since M = image size/object size, it is clear that the image is 4 times larger than the object.
- Hence it is magnified.
- The negative sign in the magnification means that the image is inverted.
Thus, the correct answer is (i) real, inverted and magnified