An object of height 4cm is placed at a distance of 30cm from the optical centre O of a convex lens of focal length 20cm. Draw a ray diagram to find the position and size of the image formed. Mark optical centre O and principal focus F on the diagram. Also find the approx. ratio of size of the image to the size of the object.
abelalex2000:
This was today's qn right??
Yaa
I know the answer
But too lazy to draw...
Yo, the magnification is-2 but ratio 2:1
yes i too got
Answers
Answered by
191
In this question I am going to use a scale of 1:5 to draw this diagram.
When I use this scale:
Focal length =20/5=4cm
Object height =4/5=0.8cm
The object distance =30/5 =6cm.
From the diagram, the image height is 1.6cm.
Which from the scale is : 1.6 × 5=8cm
The ratio of image size to object size is : 8:4=2:1
The ratio= 2:1
Find diagram in the image.
When I use this scale:
Focal length =20/5=4cm
Object height =4/5=0.8cm
The object distance =30/5 =6cm.
From the diagram, the image height is 1.6cm.
Which from the scale is : 1.6 × 5=8cm
The ratio of image size to object size is : 8:4=2:1
The ratio= 2:1
Find diagram in the image.
Attachments:
Answered by
186
We take u always in -ve.
And take f in +ve.
By calculations, v is in +ve.
We take object between f and 2f because u is -30 and it falls between 20 and 40.
The ratio is always in +ve.
See the correct diagram with solution.
Attachments:
Similar questions