KENDRIYA VIDYALAYA JAMALPUR

SECOND MONTHLY TEST

PHYSICS (XII B)

CHAPTER-I (10 MARKS) & CHAPTER -II (30 MARKS)

Time allowed : 90 minutes (Date of exam : 10/07/2020)

 

1.       Which of the following statements is incorrect?                 (1)

(a)    The net charge inside a conductor is zero in electrostatic conditions.

(b)    Electric field inside a conductor is zero in electrostatic conditions.

(c)     Electric potential is zero inside the conductor in electrostatic conditions.

(d)    Electric field inside a metallic cavity is always zero.

 

2.       Write the expression of electric field due to a dipole of dipole moment p at a distance 2d at an equatorial point.                                                                    (2)

 

3.       A positive charge Q is placed in uniform electric field E directed along positive x-axis.       (1+1+2)

(a)    What is the direction in which Q will experience electrostatic force?

(b)    How does the electrostatic potential energy of Q change with time?

(c)     After traveling a distance of x metres, find the change in electrostatic potential energy.

 

4.       Three capacitors of equal capacitances C are connected in series. Find the equivalent capacitance. How would equivalent capacitance change if the plates of middle capacitor are connected by metallic wire?  (2+1 =3)

 

5.       (a) Find the net Coulombic force on charge Q.

 

(b) Find the electric potential energy of the system.

                                                                                               

 

                                                                                (2 +2 =4)

 

 

 

6.       Using Gauss’s law, find the flux and electric field due to a line distribution of charge of charge density λ (consider line density to be uniform) at a perpendicular distance R.  (5)

 

7.       What happens to an electric dipole placed in a uniform electric field? If the dipole moment of the dipole makes angle θ with the direction of electric field, Write the expression of torque and potential energy of the dipole. [consider that PE of the dipole is 0 when θ = 90⁰ ]  (3)

 

8.       Derive an expression of work done (without acceleration) in bringing a unit positive charge q from infinity to a point inside the electric field of charge Q. Using this expression and work potential energy theorem, write the expression of potential energy. (4)

 

9.       Find the equivalent capacitance of the following combination between A and B:- (4)

 

 

 

 

 

10.   Derive an expression of potential energy stored in a capacitor of capacitance C when it is charged to a potential of V volts.                                                                                         (4)

 

11.   (a)What are dielectrics? (1)

(b)How does a dielectric of dielectric constant K change the capacitance of a capacitor when it is                 completely inserted into the volume inside a parallel plate capacitor of capacitance C?  (1)

(d)    Find the capacitance of the capacitor shown in the diagram: - (4)