If a concave mirror has a …
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If a concave mirror has a focal length of 10cm, find the two positions where an object can be placed to give, in each case, an image twice the height of the object.
Posted by Shrey Raj 7 years, 2 months ago
- 2 answers
Payal Singh 7 years, 2 months ago
Ans.
The image twice the height of the object can
A) Virtual,erect and enlarged
Or
B) Real,inverted and enlarged
1) Virtual,erect and enlarge,
in this we will take m = 2
now, m = - v / u
=>2 = - v / u
=> 2u = -v
therefore, v = -2u
1/f=(1/v)+(1/u )
=> 1/(-10)=1/(-2u) + 1/u
=> 1/-10=(-1+ 2)/2u
=> 1/-10=1/2u
-10= 2u, u=-5 cm
B) Real,inverted and enlarge ,
in this we will take, m = -2
now,m = - v / u
-2 = - v / u
- 2u = -v
therefore , v = 2u
1 / f = (1 / v )+ (1 / u)
1 / (-10) = 1 / (2u) + 1 / u
1 / - 10 = (1 + 2) / 2u
1 / - 10 = 3 / 2u
- 30 = 2u therefore , u = - 15 cm
Therefore, an image twice the height of the object can be obtained when the object is placed at
A) 5cm from the concave mirror
B) 15cm from the concave mirror
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Naveen Sharma 7 years, 2 months ago
Given f = -10 cm
magnification is twice so taking
m = +2 and -2m = -v/u
2 = -v/u
v = -2u
1/f = 1/v + 1/u
-1/10 = -1+2/2u
u = -5
Now taking magnification as -2
m = -v/u
-2 = -v/u
v = 2u
1/f = 1/v + 1/u
-1/10 = (1+2)/2u
-2u = 30 or
u = -15
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