A concave mirror has a magnification of -2.5 if its focal length is 20 cm find its image and object position? 

Asked by ajajaysanja | 23rd Oct, 2019, 11:00: AM

Expert Answer:

m =-2.5 cm 
v =?
u= ? 
f =-20 cm 
 
The linear magnification of mirror is given as 
m =-v/u 
 
therefore minus 2.5 space equals negative space v over u
therefore v space equals 2.5 space u space... space left parenthesis 1 right parenthesis

B y space m i r r o r space f o r m u l a space w e space h a v e space
1 over v plus 1 over u equals 1 over f
therefore space fraction numerator 1 over denominator 2.5 space u end fraction plus 1 over u equals space fraction numerator 1 over denominator negative 20 end fraction space
S o l v i n g space t h i s space w e space g e t comma space

u space equals space minus 28 space c m space
 
This means object distance is 28 cm and the negative sign indicates that the image is formed to the left side of the mirror. 
 
Now, substituting the value of u in equation (1), we get, 
 
v = 2.5 × (-28 cm) 
Thus, 
v = - 70 cm
 
Thus, image distance is 70 cm and the negative sign indicates that the image is also formed to the left side of the mirror. 

Answered by Shiwani Sawant | 23rd Oct, 2019, 12:19: PM