An object placed 15 cm in front of a lens forms a real image three times magnified. where is the image formed
1. 45 cm
2. 20 cm
3. 50 cm
4. 5.5 cm
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An object placed 15 cm in front of a lens forms a real image three times magnified. where is the image formed
1. 45 cm
2. 20 cm
3. 50 cm
4. 5.5 cm
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Answer:
According to new cartesian sign convention,
Object distance, u=−15 cm
Focal length of the concave mirror, f=−10 cm
Height of the object, h
0
=2 cm
According to mirror formula,
v
1
+
u
1
=
f
1
⇒
v
1
=
f
1
−
u
1
=
−10
1
−
1−5
1
=
−10
1
+
15
1
or v=−30 cm
The image is formed at a distance of 30 cm from the mirror on the same side of the object.
It is a real image.
Magnification of the mirror, m=
u
−v
=
h
0
h
1
⇒
−15
−(−30)
=
2
h
1
⇒h
I
=−4 cm.
Negative sign shows that image is inverted.
The image is real, inverted, of size 4 cm at a distance of 30 cm in front of the mirror.