anubhavclasses.worpress.com CBSE Solve Test Papers PHYSICS Class XII Chapter : Electrostatics
anubhavclasses.worpress.com CBSE TEST PAPER-05 CLASS - XII PHYSICS (Unit Electrostatics). The Plates of a charge capacitor are connecte by a voltmeter. If the plates of the capacitor are move further apart. What will be the effect on the reaing of the voltmeter?. What happens to the capacitance of a capacitor when a ielectric slab is place between its plates? 3. A steam of electrons travelling with spee m s at right angles to a uniform electric fiel E is eflecte in a circular path of raius r. Prove that e v? m re 4. The istance between the plates of a parallel plate capacitor is. A metal plate of thickness (/) is place between the plates. What will be the effect on the capacitance? 5. Keeping the voltage of the charging source constant. What woul be the percentage change in the energy store in a parallel plate capacitor if the separation between its plates were to be ecrease by 0%? 6. Two ientical plane metallic surfaces A an B are kept parallel to each other in air separate by a istance of.0 cm as shown in the figure. Surface A is given a positive potential of 0V an the outer surface of B is earthe. (a) What is the magnitue an irection of uniform electric fiel between point Y an Z? What is the work one in moving a change of 0 c from point X to Y? [] [] [] [] [3] [3] (b) Can we have non-zero electric potential in the space, where electric fiel strength is zero? anubhavclasses.worpress.com
anubhavclasses.worpress.com 7. Figure (a) an (b) shows the fiel lines of a single positive an negative changes respectively [5] (a) Give the signs of the potential ifference : Vp Vq an VB -- VA (b) Give the sign of the work one by the fiel in moving a small positive change from Q to P. (c) Give the sign of the work one by the fiel in moving a small negative change from B to A. 8. With the help of a labelle iagram, explain the principle, construction an working of a vanegraff generator. Mention its applications? ( Not in syllabus ) [5] anubhavclasses.worpress.com
anubhavclasses.worpress.com CBSE TEST PAPER-05 CLASS - XII PHYSICS (Unit Electrostatics) [ANSWERS] A o Ans 0. Since C C which means if istance increases, capacitance ecreases. Q Since V an charge on the capacitor is constant. C Hence reaing of the voltmeter increases. Ans 0. The introuction of ielectric in a capacitor reuces the effective charge on plate an hence increases the capacitance. Ans 03. The path of the electron traveling with velocity m at right angles of E is s circular. It requires a centripetal force f mv r which is provie by an electrostatic force f = ee mv ee = r e v = m Er A o Ans 04. For air C Thickness t = / only when k Î oa Co = Î oa Cmetal = ( - t) Î oa = ( - ) = Î oa
Cmatel anubhavclasses.worpress.com = Co, Hence capacitance will get ouble. Ans 05. U CV For parallel plate U A o V When = 0% of == 0.9 Then A o U' V 0.9 Change in energy = U -U = 0. U' U` U( ) U 0.9 9 AEo V ( ) 0.9 U' U 00% % change == 00 %= U 9 X 00%= U U 9 % change ==.% Ans 06. (a) v 0V Since E 000V r m. x0 (ii) Since surface A is an equipotential surface ie V 0 (b) Ans 07. (a) Work one from X to Y = Zero. V E if E=0 r V 0 v = 0 or V= constant (non zero). r So we can have non-zero electric potential, where electric fiel is zero. We know V r Vp > Vq Vp -- Vq -- Positive VA < V V -- V -- Positive B B A anubhavclasses.worpress.com
anubhavclasses.worpress.com (b) (c) Because VB is less negative then VA. In moving a positive change form Q to P work has to be one against the electric fiel so it is negative. In moving a negative change form B to A work is one along the same irection of the fiel so it is positive. Ans 08. Vanegraff generator is a evice which is capable of proucing a high potential of the orer of million volts. Principle () The charge always resies on the outer surface of hollow conuctor. () The electric ischarge in air or gas takes place reailly at the pointe ens of the conuctors. Construction:- It consist of a large hollow metallic sphere S mounte on two insulating columns A an B an an enless belt mae up of rubber which is running over two pulleys P an P with the help of an electric motor. B an B are two sharp metallic brushes. The lower brush B is given a positive potential by high tension battery an is calle a spray brush while the upper brush B connecte to the inner part of the Sphere S. Working :- When brush B is given a high positive potential then it prouces ions, ue to the action of sharp points. Thus the positive ions so prouce get spraye on the belt ue to repulsion between positive ions an the positive charge on brush B. Then it is carrie upwar by the moving belt. The pointe en of B just touches the belt collects the positive change an make it move to the outer surface of the sphere S. This process continues an the potential of the shell rises to several million volts. Applications Particles like proton, Deutrons, -- particles etc are accelerate to high spees an energies. (Not in syllabus ) anubhavclasses.worpress.com