An object is placed at a distance 20 cm from a concave mirror of focal length 15 cm. What is the image distance and nature of image formed?
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Answers
Answer:
In the present problem, the object is placed at a position which is between f and 2f so the image will be formed between infinity and 2f.
logic is had the object been at f …the image will be at infinity and if it is at 2f the image will come to 2f
using the mirror relation
1/v + 1/u = 1/f where u, v, f are object distance, image distance, and focal length respectively.
u= 20 cm f=15 cm (the sign convention is a coordinate convention with the mirror at origin and object on the positive x-axis)
so 1/v = 1/f - 1/u , = 1/15 - 1/20
= 5/(15x20)= 1/60 therefore v= 60 cm
so the image will be formed at 60 cm
with magnification m= v/u = 60/20 = 3
the image will be 3 times larger and real
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Answer:
u=−20cm,f=15cm
\bf\huge\frac{1}{f} = \frac{1}{u}+\frac{1}{v}
f
1
=
u
1
+
v
1
\bf\huge\frac{1}{v} = \frac{1}{15} - \frac{1}{-20}
v
1
=
15
1
−
−20
1
\bf\huge\frac{1}{v} = \frac{1}{15} - \frac{1}{20}
v
1
=
15
1
−
20
1
\bf\huge\frac{1}{v} = \frac{7}{60}
v
1
=
60
7