Question

An equiconvex glass lens (a) has a focal length f and power P. It is cut into two symmetrical halves (b) by a plane containing the principal axis. The two pieces are recombined as shown in fig. (c) The power of new combination is: 

                                                                      

Solution

Correct option is

Zero

Each half part has a focal length f. The rays passing through first part will converge downwards while passing through the second part, the rays will equally bend upwards. So the power of the combination will be zero.   

SIMILAR QUESTIONS

Q1

A convex mirror of focal length f produces an image (1/n)th of the size of the object. The distance of the object from the mirror is: 

Q2

A short linear object of length L lies on the axis of a spherical mirror of focal length f at a distance u from the mirror. Its image has an axial lengthL’ equal to: 

Q3

A thin convergent glass lens (μg = 1.5) has a power of +5.0 D. When this lens is immersed in a liquid of refractive index  it acts as a divergent lens of focal length 100 cm. The value of μl must be:

Q4

The sun (diameter = D) subtends an angle of θ radians at the pole of a concave mirror of focal length f. The diameter of the image of the sun formed by the mirror is: 

Q5

A double convex lens of focal length 6 cm is made of glass of refractive index 1.5. The radius of curvature of one surface is double that of the other surface. The value of smaller radius of curvature is:

Q6

Diameter of a plano-convex lens is 6 cm and thickness at the centre is 3 mm. If the speed of light in the material of the lens is , the focal length of the lens is:  

Q7

A luminous point is moving at speed v0 towards a spherical mirror, along its axis. Then the speed at which the image of this point object is moving is given by (with R = radius of curvature and u = object distance):  

Q8

A slide projector gives a magnification of 10. If it projects a slide of dimensions 3 cm × 2 cm on a screen, the area of the image on the screen will be: 

Q9

Given  There is an equiconvex lens with radius of each surface equal to 20 cm. There is air in the object space and water in the image space. The focal length of lens is:

Q10

A real image is formed by a convex lens. If we put it in contact with a concave lens and the combination again forms a real image, which of the following is true for the new image from the combination?