Combinations of Lenses & Mirrors

Q.

A convex lens A with a focal length of 20 cm and a concave lens B with a focal length of 5 cm is kept along the same axis with the distance d between them. If a parallel beam of light falling on A leaves B as a parallel beam, then distance d in cm will be

1. 25
2. 15
3. 30
4. 50

Q.

A convex lens of a focal length of 20 cm can produce a magnified virtual as well as a real image. Is this a correct statement? If yes, where shall the object be placed in each case for obtaining these images?

Q. Focal length of the objective and eyelenses of a telescope are 200 cm and 5 cm. The maximum magnifying power of the telescope is

1. 40
2. 48
3. 60
4. 100

Q. A plano-convex lens is made of a material of refractive index $n$. When a small object is placed $30cm$ away in front of the curved surface of the lens, an image of double the size of the object is produced. Due to reflection from the convex surface of the lens, another faint image is observed at a distance of $10cm$ away from the lens. Which of the following statement (s) is (are) true?

1. The refractive index of the lens is $2.5$
2. The radius of curvature of the convex surface is $45$ cm
3. The faint image is erect and real
4. The focal length of the lens is $20$ cm

Q.

A double convex lens has power $P$ and same radii of curvature $R$ of both the surfaces. The radius of curvature of a surface of a plano-convex lens made of the same material with power $1.5P$ is

1. $R/3$

2. $3R/2$

3. $R/2$

4. $2R$

Q.

What are Paraxial Rays?

Q. A parallel beam of monochromatic light falls on a combination of a convex lens and a concave lens of focallengths 15 cm and 5 cm respectively. What is the distance between the two lenses to obtain a parallel beanmof light from the concave lens?(1) 20 cm(2) 3 cm() 10 cm(4) 45 cm

Q. A luminous object is placed at a distance of 30 cm from the convex lens of focal length 20 cm. On the other side of the lens, at what distance from the lens a convex mirror of radius of curvature 10 cm be placed in order to have an upright image of the object coincident with it

1. 12 cm
2. 50 cm
3. 60 cm
4. 30 cm

Q. A biconvex lens made of a transparent material of refractive index 1.25 is immersed in water of refractive index 1.33. Will the lens behave as a converging lens or a diverging lens? Give reason.

Q. A thin equiconvex glass lens of refractive index 1.5 has power of 5D. When the lens is immersed in a liquid of refractive index u, it acts as a divergent lens of focal length 100 cm. The value of liquid is of (1) 4/3 (2) 3/4 (3) 5/3 (4) 8/3 ter 8 P Rod

Q. An upright object is placed at a distance of $40cm$ in front of a convergent lens of focal length $20cm$. A convergent mirror of focal length $10cm$ is placed at a distance of $60cm$ on the other side of the lens. The position and size of the final image will be

1. $40cm$ from the convergent lens, same size as the object
2. $20cm$ from the convergent mirror, same size as the object
3. $20cm$ from the convergent mirror, twice the size as the object
4. $40cm$ from the convergent mirror, twice the size as the object

Q.

Explain the construction and working of a compound microscope with a neat ray-diagram.

Q. A concave mirror of focal length $20cm$ and a convex lens of focal length $10cm$ are kept with their optic axis parallel but separated by $0.5mm$ as shown in the figure. The distance between the lens and the mirror is $10cm$. An object of height $3mm$ is placed on the optical axis of the lens at a distance of $15cm$ from the lens. Find the height of the image (in $mm$) formed by the mirror after refraction from the lens.

IMAGE

Q. What should be the value of distance $d$ so that final image is formed on the object itself? (Focal lengths of the lenses are written on the lenses.)

1. $10cm$
2. $20cm$
3. $5cm$
4. None of these

Q.

A convex lens is in contact with a concave lens. The magnitude of the ratio of their focal lengths is 23 . Their equivalent focal length is 30 cm. What are their individual focal lengths?(in cm)

1. -10, 15
2. –15, 10
3. –75, 25
4. –75, 50

Q. In the situation shown in the figure, three lenses of focal lengths $20\text{cm},30\text{cm}$ and $36\text{cm}$ are held coaxial such that separation between first and second lens is $12\text{cm}$ and between second and third lens is $10\text{cm}$. If the final image of an object at a distance of $30\text{cm}$ from first lens is at a distance $10x\text{cm}$ from the middle lens, then find the value of $x$.

Q. A combination of two thin lenses with focal lengths $f_1$ and $f_2$ respectively forms an image of distant object at distance 60 cm when lenses are in contact. The position of this image shifts by 30 cm towards the combination when two lenses are separated by 10 cm. The corresponding values of $f_1$ and $f_2$ are

1. 30 cm, - 60 cm
2. 20 cm, - 30 cm
3. 15 cm, - 20 cm
4. 12 cm, – 15 cm

Q. The equiconvex lens of glass refractive index 1.5 of focal length 10 cm in air is silvered on one side it will behave lik

Q. A concave mirror is placed on a horizontal table with its axis directed vertically upwards. Let O be the pole of the mirror and C its centre of curvature. A point object is placed at C. It has a real image, also located at C. If the mirror is now filled with water, the image will be

1. Real, and will remain at C
2. Real, and located at a point between C and $\infty$
3. Virtual and located at a point between C and O
4. Real, and located at a point between C and O

Q. The plane surface of a plano- convex lens is silvered. If $\mu$ be the refractive index and $R$, the radius of curvature of curved surface, then the system will behave like a concave mirror of radius of curvature of

1. $\mu R$
2. $\frac{R}{(\mu -1)}$
3. $\frac{R^2}{\mu }$
4. $\left(\frac{\mu +1}{\mu -1}\right)R$

Q. a convex lens is placed in contact with a plane mirror a point object on the axis at a distance 30 cm from this combination has its image considering with itself the focal length of the convex lenses

Q. A convex lens of focal length $10\text{cm}$ is placed $30\text{cm}$ in front of a second convex lens also of the same focal length. A plane mirror is placed after the two lenses. Where should a point object be placed in front of the first lens so that it images on to itself ?

1. $20\text{cm}$
2. $15\text{cm}$
3. $30\text{cm}$
4. $25\text{cm}$

Q. An eye specialist prescribes spectacles having combination of convex lens of focal length $40\text{cm}$ in contact with a concave lens of focal length $25\text{cm}$. The power of this lens combination in diopters is

1. $+1.5$
2. $+6.67$
3. $-6.67$
4. $-1.5$

Q.

Two thin convex lenses of focal lengths 20cm and 5cm respectively are placed at a distance s. If a parallel beam incident in the first lens emerges as a parallel beam from the second lens then the value of d is

Q.

In a concave mirror when the object is located beyond C the magnification is

Q.

A double convex thin lens made of glass of refractive index 1.6 has radii of curvature 15 cm each. The focal length of this lens when immersed in a fluid of refractive index 1.63 is

1. 25 cm

2. + 250 cm

3. 125 cm

4. - 416.67 cm

Q.

Explain the lens with its types and working.

Q.

A convex lens is cut in half along its principal axis and the two halves are separated by a distance of 12 cm. An object is placed 6 cm in front of the lens as shown in Figure. Two sharp images are formed on the screen placed 80 cm from the object. What is the focal length of the lens ?

1. 23.45 cm
2. 17.30 cm
3. 12.50 cm
4. 19.55 cm

Q. Assertion :The minimum distance between an object and its real image formed by a convex lens is ${}^{\prime }2f{}^{\prime }$ Reason: The distance between object and its real image is minimum when its magnification is one.

1. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
2. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
3. Assertion is incorrect but Reason is correct.
4. Both Assertion and Reason are incorrect

Q. A liquid of refractive index $1.6$ is contained in the cavity of a glass specimen of refractive index $1.5$ as shown in figure. If each of the curved surfaces has a radius of curvature of $0.20\text{m}$, the arrangement behaves as a

1. converging lens of focal length $0.25\text{m}$
2. converging lens of focal length $0.72\text{m}$
3. diverging lens of focal length $0.25\text{m}$
4. diverging lens of focal length $0.17\text{m}$