Numaricals onoptical instruments [3m]
Answers
Answer:
An h-high object is placed at a distance that smaller than focal length f. Determine the properties of the image.
Solution
Optical instruments – problems and solutions 1
According to the figure above, properties of the image are virtual, upright and greater than an object.
2. If an object is placed at the center between the focal point and the concave mirror, the image formated by mirror are :
1. Greater 2 times than object
2. Upright
3. Image distance = focal length
4. Virtual
The correct statement is…..
Solution :
Focal length (f) = 20 cm and object distance (do) = 10 cm, as figure shown below :
a) Image distanceOptical instruments – problems and solutions 2
1/f = 1/do + 1/di
1/20 = 1/10 + 1/di
1/20 – 1/10 = 1/di
1/20 – 2/20 = 1/di
-1/20 = 1/di
di = -20 cm
The minus sign indicates that the image is virtual o
b) Magnification of image
M = -di / do = -(-20)/10 = 20/10 = 2 times
The plus sign indicates that the image is upright and the image is greater 2 times than object.
Properties of image
1. Image 2 times greater than the object
2. Upright
3. Image distance = focal length = 20 cm