A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is
  • a)
    - 30 cm
  • b)
    - 20 cm
  • c)
    - 40 cm
  • d)
    - 60 cm
Correct answer is option 'B'. Can you explain this answer?

Class 10 Question

By Azahruddin · Jun 13, 2020 ·Class 10
9 Answers
Tanishka Gupta answered Jun 13, 2020
H0=10mm hi=5mm v=−30cm
Here  given ,
Now we know
m=−v u =hi ho ⇒u=−vho hi =−30*10 5 =−60 cm  Now using mirror formula  1 f =1 v +1 u =1 −30 +1 −60 =−1 20 Hence f=−20 cm

Nirmal Kumar answered Feb 15, 2020
V=-30cm,ho=10mm=1cm,hi=5mm=0.5cm,f=?,we know that-->hi/ho=-v/u,0.5/1=-(-30)/u,u=60cm,by mirror formula-->1/f=1/v-1/u,1/f=1/30-1/(60),1/f=3/(-60),f=-60/3=-20 cm

Likshika Sethi answered Aug 19, 2020
-20 is correct answer

Shiwangi Bansal answered 2 weeks ago
B) -20 cm is the answer

Jerome Job answered 3 weeks ago
Height of the object = 10mm ->1cm
height if the image =( -5mm)->-0.5cm
m=hi/ho, v=(-30cm)
m=( -0.5)/1=(-0.5)
m=(-v/u)
(-0.5)=-(-30)/u
u=(-60cm)
1/v+1/u=1/f
1/-30+(-1/60)=1/f
f=(-20cm)

M.mukesh answered 3 weeks ago
-20 cm or 200mm

This discussion on A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror.The focal length of this mirror isa)- 30 cmb)- 20 cmc)- 40 cmd)- 60 cmCorrect answer is option 'B'. Can you explain this answer? is done on EduRev Study Group by Class 10 Students. The Questions and Answers of A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror.The focal length of this mirror isa)- 30 cmb)- 20 cmc)- 40 cmd)- 60 cmCorrect answer is option 'B'. Can you explain this answer? are solved by group of students and teacher of Class 10, which is also the largest student community of Class 10. If the answer is not available please wait for a while and a community member will probably answer this soon. You can study other questions, MCQs, videos and tests for Class 10 on EduRev and even discuss your questions like A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror.The focal length of this mirror isa)- 30 cmb)- 20 cmc)- 40 cmd)- 60 cmCorrect answer is option 'B'. Can you explain this answer? over here on EduRev! Apart from being the largest Class 10 community, EduRev has the largest solved Question bank for Class 10.