Q22 of 26 Page 1

Three circuits, each consisting of a switch ‘S’ and two capacitors, are initially charged, as shown in the figure. After the switch has been closed, in which circuit will the charge on the left-hand capacitor (i) increase, (ii) decrease and (iii) remain same? Give reasons.

1.PNG


Charge flows in the circuit until both the capacitors are at same potential. We know, that the potential, V = q/c


Vleft = 6Q/2C = 3Q/C and Vright =3Q/C


⇒ Vleft = Vright


Therefore, voltage in left capacitor stays the same.


Vleft = 6Q/C and Vright = 3Q/C


⇒ Vleft > Vright


Therefore, voltage in left capacitor will decrease.


Vleft = 6Q/3C = 2Q/C and Vright = 3Q/C


⇒ Vleft < Vright


Therefore, voltage in left capacitor will increase


More from this chapter

All 26 →
20

Name the three different modes of propagation in a communication system. State briefly why do the electromagnetic waves with frequency range from a few MHz up to 30 MHz can reflect back to the earth. What happens when the frequency range exceeds this limit?

 21

Define the terms ‘stopping potential’ and ‘threshold frequency’ in relation to photoelectric effect. How does one determine these physical quantities using Einstein’s equation?

 23 SECTIO

Sunita and her friends visited an exhibition. The policeman asked them to pass through a metal detector. Sunita’s friends were initially scared of it. Sunita, however, explained to them the purpose and working of the metal detector. Answer the following questions:

(a) On what principle does a metal detector work?


(b) Why does the detector emit sound when a person carrying any metallic object walks through it?


(c) State any two qualities which Sunita displayed while explaining the purpose of walking through the detector.


 24

(a) A point-object is placed on the principal axis of a convex spherical surface of radius of curvature R, which separates the two media of refractive indices n1 and n2 (n2 > n1). Draw the ray diagram and deduce the relation between the distance of the object (u), distance of the image (v) and the radius of curvature (R) for refraction to take place at the convex spherical surface from rarer to denser medium.

(b) Use the above relation to obtain the condition on the position of the object and the radius of curvature in terms of n1 and n2 when the real image is formed.


OR


(a) Draw a labelled ray diagram showing the formation of image by a compound microscope in normal adjustment. Derive the expression for its magnifying power.


(b) How does the resolving power of a microscope change when


(i) the diameter of the objective lens is decreased,


(ii) the wavelength of the incident light is increased? Justify your answer in each case.