JEE MAINS -2014: Revision : Eletcric charge , current and Modern Physics1-In a spherical region, electric potential at distance r from the center , say O, of the region, electric potential is a r2 + b where a and b are constants. How much is the charge enclosed with a spherical volume of radius r with center at O ?

2-In the previous problem, what is the charge density at distance r from O ?

3-A positive point charge Q is placed on the equator of an electric dipole of dipole moment p, at large distance r from the dipole. The magnitude and the direction of force on the dipole by the point charge will be (a) p Q/ ( 4 €0 r2 ) in direction parallel to p vector(b) p Q/ ( 4 €0 r3 ) in direction parallel to p vector(c) p Q/ ( 4 €0 r3 ) in direction anti parallel to p vector

4-A point charge Q is placed at distance 3 R from the center of an uncharged conductor of radius R. The resulting potential and the electric field , at the center of conductor will be (a) zero, zero (b) Q/ ( 12 €0 R) and zero(c) Q/ ( 8 €0 R) and Q/ ( 36 €0 R2) (d) none of these

5- Ionization potential for hydrogen atom is 13.6 V. The radius of the electron orbit in ground state of hydrogen atom is r0. The value of the expression e2 / ( 4 €0 r0 ) is equal to (a) 13.6 eV (b) 27.2 eV (c) 6.8 eV (d) none of these

6- The line connecting the electron of hydrogen atom to the nucleus, sweeps area A in time t when the atom is in ground state. How much area is swept by the line connecting the electron to the nucleus , in a singly ionized helium atom in first excited state, in time t ?(a) A (b) 2 A (c) A/ 2 (d) 4 A

7- In a hydrogen like atom , when electron has kinetic energy is E1 , its angular momentum is L1 and when kinetic energy is E2 , its angular momentum is L2. If E1/E2 equals ( L1/L2 ) x , then x is equal to (a) 2 (b) -1/2 (c) -1 (d) -2

8- The equi potential line passing form point ( 2,1), in a region where electric field is uniform and its direction is along unit vector {3 i - 4 j } / 5 , is given by (a) 3 x – 4 y = 2 (b) 3 x + 4 y = 10 (c) 4 x + 3 y = 11 (d) 4 x = 3 y

9- A circular ring uniformly charged is fixed. A charge particle of mass m is released from center of the ring. The particle

reaches at certain point P on the axis , with speed v0. Now the particle is stopped and then projected to wards the center of ring with velocity 2 v0 . The will reach at the center of the ring with velocity (a) v0 (b) v0√ 2 (c) v0√ 3 (d) v0 / √ 2

10-A galvanometer is shunted with a wire of resistance whose resistance is 99 times lesser than the galvanometer resistance. The current sensitivity of the instrument now and before will be in ratio(a) 1: 99 (b) 99 :1 (c) 1:100 (d) 100 :1

11- In the fig shown the cell has emf E = 1volt and the capacitance is 5 μF . The points A and B are at potentials 8 and 3 volts respectively. The charge on the left plate of the capacitor will be (a) 30 μC (b) -30 μC (c) 20 μC (d) -20 μC

12- A parallel plate capacitor, with separation d1 between the plates , is charged up to potential V0. After disconnecting the cell , the separation between the plates is changed to d2 . Final value of the electric field in space between the plates will be (a) V0 / d1 (b) V0 / d2 (c) V0 d1

2 / d2 (d) none 13- In the previous problem if the energy stored in the capacitor was u initially, then the work done, in changing the plate separation against the electrostatic forces , will be (a) U ( d2 –d1 ) (b) U ( d2 /d1 -1) (c) U ( d2

2 /d12 -1)

14- A capacitor X of capacitance 1 μ F withstands a maximum voltage 6 kV while a capacitor Y of capacitance 2 μ F withstands the maximum voltage 4 kV . What maximum voltage will the system of these capacitors withstand if they are connected in series?(a) 10 kV (b) 9 kV (c) 12 kV (d) 15 kV

15- In the fig six identical capacitors each of capacitance Care connected. The equivalent capacitance between the points A and B is (a) 2 C (b) C /3 (c) 2C / 3 (d) C / 2

**16- A capacitor is being discharged through a resistor. In two successive seconds, heat dissipation through the resistor are H1

JEE MAINS -2014: Revision : Eletcric charge , current and Modern Physics

and H2 respectively. How much heat will be produced in the resistor in the next one second?(a) H1 - H2 (b) H2

2/ H1 (c) H1 2/ H2 (d) 2H2 -

H1

17- Mark incorrect one ?(a) Water has large dielectric constant because it is polar(b) Polar dielectric mediums are temperature sensitive(c) The atomic electric dipole moment of non polar dielectrics is zero before they are exposed to electric nfield(d) The dielectric constant of polar dielectrics increases with rise in the temperature.

18- Taking capacitance ( C ) as fundamental quantity instead of current, dimensional formula for potential will be (a) M1/2 L T-1 C-1/2 (b) M 2 L T-1 C3 (c) M1/2 L T-2 C-1 (d) none of these

19- Uniform electric field 50 V / m exist in positive x- direction . Points A and B are situated at (2 m,5 m) and (6 m, 7 m). If the electric potential at A is 40 volts, then at B , electric potential will be …….

20- Find k if after closing switch s, cell of emf 3 volt does not draw any current ?

21-A cell of emf 6 volt , is connected to a voltmeter and an ammeter placed in series. After a resistor is connected in parallel to the voltmeter, its reading decreases by factor 2 and reading of the ammeter increases by factor 2. What was the reading of the voltmeter after connecting the resistance in parallel ?

22- At distance 10cm from a long uniformly charged thread, a proton is released from rest. Its velocities at distances 20cm , 40 cm and 80 cm from the thread are found as x,y and z respectively. The relation between x,y and z will be …

23- In the circuit shown what will be steady state potential across the resistor, capacitor and inductor separately ?

24-Two concentric thin spherical shells of radii R and 3R are carrying charges Q1 and Q2 respectively distributed uniformly over them. If a charge q , of same sign as Q1 and Q2 , is released

from rest just outside the inner shell, what will be its kinetic energy while reaching to the outer shell ?

***25-Two point charges are placed at points A and B on the x-axis. The graph between the electric potential and the position on x-axis is shown. .Guess the sign of the two charges and compare their magnitudes .