Download Physics

PHYSICS
CHAPTER:- ELECTROSTATICS
VERY SHORT ANSWER TYPE (1 Marks)
1. The field lines of a negative point change are as shown in figure. Does the Kinetic Energy
of a small negative change increase or decrease in going from B to A?
2. Two equal balls having equal positive charge ‘q’ coulomb are suspended by two
insulating strings of equal length. What would be the effect on the force when a plastic
sheet is inserted between the two?
3. Define electric dipole moment. Write its S.I unit.
4. A hollow metal sphere of radius 10cm is changed such that the potential on its surface is
5V . What is the potential at the centre of sphere?
5. A point charge Q is placed at point O as dhown in figure . Is the potential difference (VA VB ) positive,negative or zero, if Q is
i)positive
ii)negative
6. Name the physical quantity whose S.I unit is JC-1. Is it scalar or a vector quantity?
7. What is electrostatic potential due to an electric dipole at an equatorial point?
8. What is the work done to move a test charge ‘q’ from a distance of 1cm along the
equatorial axis of electric dipole?
9. Two charges of magnitude -3Q and +2Q are located at (4,0) and (4a,0) respectively .
What is the electric flux due to these charges through a sphere of radius 5a with its
centre at origin?\
10. A charge ‘q’ is placed at the centre of cube of side length l . What is the electric flux
passing through each face of the cube?
2 MARKS QUESTION
1. A capacitor made of two parallel plates each of area A and separation d, is being
charged by an external ac source, show that displacement of current inside the
capacitor is the same as the current charging at the capacitor.
2. A slab of material of dielectric constant k has the same area as that of plates of a
parallel plate capacitor but has the thickness d/3. Where d is the separation
between the plates. Find out the expression for its capacitance when the slab is
inserted between the plate of the capacitor.
3. A parallel plate capacitor of the capacitance C is changed to potential V. It is then
connected to another unchanged capacitor having the same capacitance. Find out
ratio of the energy stored in combine system to that stored initially in the singular
capacitor.
4. A test charge ‘q’ is moved without acceleration from A to C along the path from A to
B and then from B to C in electric field E as shown in the fig.
I) Calculate the potential difference between A to C.
II) At which point (of the two) is the electric potential is more and why?
5. An electric dipole is held in uniform electric field
I) Show that the net force on it is 0.
II) The dipole is aligned paralleled to the the field. Find the work done in rotating
through an angle 180.
6. A spherical conducting sheet if inner radius r1 and outer radius r2 has a charge Q. A
charge q is placed at the center of the sheet.
I) What is the surface charge density on the
a) Inner surface
b) Outer surface of the shell
II) Write one expression for the electric field at a point x>r2 from the center of the
shell.
7. Show that the electric field at the surface of a charged conductor is given by
E= (sigma/ Epsilon not)x n(cap), where sigma is the surface charged density nd A is
the unit vector normal to the surface in outward direction.
3 MARKS QUESTION
1. Find the equivalent capacitance of the network shown in the fig., whom each capacitoris
of 1mueF. When the ends of X and Yare connected to a ^v battery, find out
I) The change and
II) the energy stored at the network .
2. Deduce the expression for the electrostatic energy stored in a capacitor of capacitance
‘c’and having charge ‘Q’.
i)
How will the energy stored and
ii)
The electric field inside the capacitance be affected when it is completely filled
with a dielectric material of dielectric const. ‘Q’.
3. A network of $ capacitor each of 12 mueF capacitance is connectedto 500v supply as
given in fig. determine
a) Equivalence capacitance
b) Change on each capacitor.
5 MARKS QUESTION
1. Using Gauss’s law deduce the expression for the electric field due to uniformly charged
spherical conducting shell of radius R at a point:
Outside the shell and inside the shell.
Or
a) Define Electric dipole moment . Is it a scalar quantity or vector? Derive the
expression for the electric field of a dipole at a point on the equatorial plane of the
dipole.
b) Draw the equatorial surface due to an electric dipole. Locate the point where
potential due to the dipole is 0.
2. a)” The outward electric flux due to charge +Q is independent of the shape and size of
the surface which encloses it”. Give two reasons to justify this statement.
c) Two identical circular loops ‘1’ and ‘2’ of radius R each have linear charge density –
lamda and +lamda C/m respectively . The loop are placed coaxially with their center
Q(3)1/2 distance apart. Find the magnitude and direction of the net electric field at
the center of the loop’1’.
3. Draw a labeled diagram of Van de Graraff generator state its working principle to show
how by introducing a small changed sphere into a larger sphere, a large amount of
charge can be transferred to the outer sphere. State the use of this machine and also
point out its limitation.
4. a) Deduce the expression for the torque acting on the dipole of the dipole moment P in
the presence of uniform electric field E.
b) Consider two hollow concentric sphere, S1and S2, enclosing charges 2Q and 4Q
respectively as in the fig.
i) Find out the ratio of electric flux through them.\
ii) How will the electric flux in the sphere will change if a medium of dielectric
constant ‘cr ‘ is introduced in he space inside S1in the place of air?
Deduce necessary expression.
5. Use the gauss theorem and derive the expression for the expression for electric field
between uniformly charged large parallel sheets with surface charge density –sigma,
+sigma respectively.