364748
A convex lens is made of 3 layers of glass of 3 different materials as in the figure. A point object is placed on its axis. The number of images of the object are
1 3
2 4
3 1
4 2
Explanation:
All three materials are distributed symmetrically about the optical axis of the lens. Hence each ray of light passing through the lens experiences similar refraction and the combination acts as a single lens. Therefore, only one image of the point object is formed.
KCET - 2008
PHXII09:RAY OPTICS AND OPTICAL INSTRUMENTS
364749
Two lenses of power \( + 2.50\,D\) and \( - 3.75\,D\) are combined to form a compound lens. Its focal length in \( cm\) will be -
364750
Two lenses are placed in contact with each other and the focal length of combination is \(80\,cm\). If the focal length of one is \(20\,cm\), then the power of the other will be:
1 \(1.66\,D\)
2 \(4.00\,D\)
3 \( - 1.00\,D\)
4 \( - 3.75\,D\)
Explanation:
\(\dfrac{1}{F}=\dfrac{1}{f_{1}}+\dfrac{1}{f_{2}} \Rightarrow \dfrac{1}{80}=\dfrac{1}{20}+\dfrac{1}{f_{2}}\) \(=\dfrac{1}{f_{2}}=\dfrac{1}{80}-\dfrac{1}{20}\) \(\frac{1}{{{f_2}}} = \frac{{1 - 4}}{{80}} = {f_2} = - \frac{{80}}{3}\;cm\) \(\therefore\) Power of second lens \({P_2} = \frac{{100}}{{{f_2}}} = \frac{{100}}{{\frac{{ - 80}}{3}}} = - 3.75\,D.\)
PHXII09:RAY OPTICS AND OPTICAL INSTRUMENTS
364751
An effective power of a combination of 5 identical convex lenses which are kept in contact along the principal axis is \(25\,D.\) Focal length of each of the convex lens is
1 \(20\,cm\)
2 \(25\,cm\)
3 \(500\,cm\)
4 \(50\,cm\)
Explanation:
\(P_{e f f}=25 D\)
Let the power of each lens be \(P\). \(P_{e f f}=P+P+P+P+P\) \(25 = 5\,P \Rightarrow P = 5\,D\) \(f = \frac{1}{P} = \frac{1}{5}m = \frac{{100}}{5}\;cm = 20\;cm\)
364748
A convex lens is made of 3 layers of glass of 3 different materials as in the figure. A point object is placed on its axis. The number of images of the object are
1 3
2 4
3 1
4 2
Explanation:
All three materials are distributed symmetrically about the optical axis of the lens. Hence each ray of light passing through the lens experiences similar refraction and the combination acts as a single lens. Therefore, only one image of the point object is formed.
KCET - 2008
PHXII09:RAY OPTICS AND OPTICAL INSTRUMENTS
364749
Two lenses of power \( + 2.50\,D\) and \( - 3.75\,D\) are combined to form a compound lens. Its focal length in \( cm\) will be -
364750
Two lenses are placed in contact with each other and the focal length of combination is \(80\,cm\). If the focal length of one is \(20\,cm\), then the power of the other will be:
1 \(1.66\,D\)
2 \(4.00\,D\)
3 \( - 1.00\,D\)
4 \( - 3.75\,D\)
Explanation:
\(\dfrac{1}{F}=\dfrac{1}{f_{1}}+\dfrac{1}{f_{2}} \Rightarrow \dfrac{1}{80}=\dfrac{1}{20}+\dfrac{1}{f_{2}}\) \(=\dfrac{1}{f_{2}}=\dfrac{1}{80}-\dfrac{1}{20}\) \(\frac{1}{{{f_2}}} = \frac{{1 - 4}}{{80}} = {f_2} = - \frac{{80}}{3}\;cm\) \(\therefore\) Power of second lens \({P_2} = \frac{{100}}{{{f_2}}} = \frac{{100}}{{\frac{{ - 80}}{3}}} = - 3.75\,D.\)
PHXII09:RAY OPTICS AND OPTICAL INSTRUMENTS
364751
An effective power of a combination of 5 identical convex lenses which are kept in contact along the principal axis is \(25\,D.\) Focal length of each of the convex lens is
1 \(20\,cm\)
2 \(25\,cm\)
3 \(500\,cm\)
4 \(50\,cm\)
Explanation:
\(P_{e f f}=25 D\)
Let the power of each lens be \(P\). \(P_{e f f}=P+P+P+P+P\) \(25 = 5\,P \Rightarrow P = 5\,D\) \(f = \frac{1}{P} = \frac{1}{5}m = \frac{{100}}{5}\;cm = 20\;cm\)
364748
A convex lens is made of 3 layers of glass of 3 different materials as in the figure. A point object is placed on its axis. The number of images of the object are
1 3
2 4
3 1
4 2
Explanation:
All three materials are distributed symmetrically about the optical axis of the lens. Hence each ray of light passing through the lens experiences similar refraction and the combination acts as a single lens. Therefore, only one image of the point object is formed.
KCET - 2008
PHXII09:RAY OPTICS AND OPTICAL INSTRUMENTS
364749
Two lenses of power \( + 2.50\,D\) and \( - 3.75\,D\) are combined to form a compound lens. Its focal length in \( cm\) will be -
364750
Two lenses are placed in contact with each other and the focal length of combination is \(80\,cm\). If the focal length of one is \(20\,cm\), then the power of the other will be:
1 \(1.66\,D\)
2 \(4.00\,D\)
3 \( - 1.00\,D\)
4 \( - 3.75\,D\)
Explanation:
\(\dfrac{1}{F}=\dfrac{1}{f_{1}}+\dfrac{1}{f_{2}} \Rightarrow \dfrac{1}{80}=\dfrac{1}{20}+\dfrac{1}{f_{2}}\) \(=\dfrac{1}{f_{2}}=\dfrac{1}{80}-\dfrac{1}{20}\) \(\frac{1}{{{f_2}}} = \frac{{1 - 4}}{{80}} = {f_2} = - \frac{{80}}{3}\;cm\) \(\therefore\) Power of second lens \({P_2} = \frac{{100}}{{{f_2}}} = \frac{{100}}{{\frac{{ - 80}}{3}}} = - 3.75\,D.\)
PHXII09:RAY OPTICS AND OPTICAL INSTRUMENTS
364751
An effective power of a combination of 5 identical convex lenses which are kept in contact along the principal axis is \(25\,D.\) Focal length of each of the convex lens is
1 \(20\,cm\)
2 \(25\,cm\)
3 \(500\,cm\)
4 \(50\,cm\)
Explanation:
\(P_{e f f}=25 D\)
Let the power of each lens be \(P\). \(P_{e f f}=P+P+P+P+P\) \(25 = 5\,P \Rightarrow P = 5\,D\) \(f = \frac{1}{P} = \frac{1}{5}m = \frac{{100}}{5}\;cm = 20\;cm\)
364748
A convex lens is made of 3 layers of glass of 3 different materials as in the figure. A point object is placed on its axis. The number of images of the object are
1 3
2 4
3 1
4 2
Explanation:
All three materials are distributed symmetrically about the optical axis of the lens. Hence each ray of light passing through the lens experiences similar refraction and the combination acts as a single lens. Therefore, only one image of the point object is formed.
KCET - 2008
PHXII09:RAY OPTICS AND OPTICAL INSTRUMENTS
364749
Two lenses of power \( + 2.50\,D\) and \( - 3.75\,D\) are combined to form a compound lens. Its focal length in \( cm\) will be -
364750
Two lenses are placed in contact with each other and the focal length of combination is \(80\,cm\). If the focal length of one is \(20\,cm\), then the power of the other will be:
1 \(1.66\,D\)
2 \(4.00\,D\)
3 \( - 1.00\,D\)
4 \( - 3.75\,D\)
Explanation:
\(\dfrac{1}{F}=\dfrac{1}{f_{1}}+\dfrac{1}{f_{2}} \Rightarrow \dfrac{1}{80}=\dfrac{1}{20}+\dfrac{1}{f_{2}}\) \(=\dfrac{1}{f_{2}}=\dfrac{1}{80}-\dfrac{1}{20}\) \(\frac{1}{{{f_2}}} = \frac{{1 - 4}}{{80}} = {f_2} = - \frac{{80}}{3}\;cm\) \(\therefore\) Power of second lens \({P_2} = \frac{{100}}{{{f_2}}} = \frac{{100}}{{\frac{{ - 80}}{3}}} = - 3.75\,D.\)
PHXII09:RAY OPTICS AND OPTICAL INSTRUMENTS
364751
An effective power of a combination of 5 identical convex lenses which are kept in contact along the principal axis is \(25\,D.\) Focal length of each of the convex lens is
1 \(20\,cm\)
2 \(25\,cm\)
3 \(500\,cm\)
4 \(50\,cm\)
Explanation:
\(P_{e f f}=25 D\)
Let the power of each lens be \(P\). \(P_{e f f}=P+P+P+P+P\) \(25 = 5\,P \Rightarrow P = 5\,D\) \(f = \frac{1}{P} = \frac{1}{5}m = \frac{{100}}{5}\;cm = 20\;cm\)
