Q22 of 30 Page 1

A convex lens of focal length 20 cm is placed coaxially with a convex mirror of radius of curvature 20 cm. The two are kept at 15 cm apart. A point object lies 60 cm in front of the convex lens. Draw a ray diagram to show the formation of the image by the combination. Determine the nature and position of the image formed.

Given: -


focal length of convex lens is, f = +20 cm


Object distance from the lens, u = -60 cm


Distance between the mirror and the lens, d = 15 cm,


Focal length of the mirror, f = +10 cm


Formula: -


The lens formula,



f is the focal length of the lens, v is the image distance, u is the object distance


The mirror formula,



f is the focal length of the mirror, v is the image distance, u is the object distance


Calculations: -



for the lens,


applying the lens formula,



After solving we get,


v’ = +30 cm


This image is the object for the mirror, which is formed at 15 cm behind the mirror, so this is the case of a virtual object


Applying the mirror formula, we get,



After solving we get,


v = +30 cm


So, the final image is formed 30 cm behind the mirror is virtual in nature.


More from this chapter

All 30 →
20

Define the term 'mutual inductance' between the two coils. Obtain the expression for mutual inductance of a pair of long coaxial solenoids each of length l and radii r1 and r2 (r2 >> r1). Total numbers of turns in the two solenoids are N1 and N2, respectively.

 21

Answer the following:

(a) Why are the connections between the resistors in a meter bridge made of thick copper strips?


(b) Why is it generally preferred to obtain the balance point in the middle of the meter bridge wire?


(c) Which material is used for the meter bridge wire and why?


OR


A resistance of R Ω draws current from a potentiometer, as shown in the figure. The potentiometer has a total resistance Ro Ω. A voltage V is supplied to the potentiometer. Derive an expression for the voltage across R when the sliding contact is in the middle of the potentiometer.


 23

A voltage V = V0 sin ωt is applied to a series LCR circuit. Derive the expression for the average power dissipated over a cycle. Under what condition:

(i) no power is dissipated even though the current flows through the circuit,


(ii) maximum power is dissipated in the circuit?

 24

Write any two distinguishing features between conductors, semiconductors and insulators on the basis of energy band diagrams.