Q 1.1: What is the force between two small charged spheres having charges of 2 \times 10^{-7}C and 3 \times 10^{-7}C placed 30 cm apart in air?

Q 1.2: The electrostatic force on a small sphere of charge 0.4 \mu C due to another small sphere of charge -0.8 \mu C in air is -0.2N. (a) What is the distance between the two spheres?  

Q 1.2: The electrostatic force on a small sphere of charge 0.4 \mu Cdue to another small sphere of charge -0.8 \mu C in air is 0.2N.(b)What is the force on the second sphere due to the first?

Q 1.3: Check that the ratio \frac{ke^{2}}{Gm_{e}m_{p}} is dimensionless. Look up a Table of Physical Constants and determine the value of this ratio. What does the ratio signify?

Q 1.4 (a): Explain the meaning of the statement ‘electric charge of a body is quantised’.

Q 1.4 (b) Why can one ignore quantisation of electric charge when dealing with macroscopic i.e., large scale charges?

Q 1.5: When a glass rod is rubbed with a silk cloth, charges appear on both. A similar phenomenon is observed with many other pairs of bodies. Explain how this observation is consistent with the law of conservation of charge.

Q 1.6: Four point charges q_{A}= 2 \mu C, q_{B}= -5 \mu C, q_{C}= 2 \mu C, and q_{D}= -5 \mu C are located at the corners of a square ABCD of side 10 cm. What is the force on a charge of 1 μC placed at the centre of the square?

Q 1.7(a): An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not?

Q 1.7 (b): Explain why two field lines never cross each other at any point?

Q 1.8(a): Two point charges q_{A}=3 \mu C and q_{B}=-3 \mu C are located 20 cm apart in vacuum. (a) What is the electric field at the midpoint O of the line AB joining the two charges?

Q 1.8(b): Two point charges q_{A}=3\mu C and q_{B}=-3\mu C are located 20 cm apart in vacuum. If a negative test charge of magnitude1.5 \times 10^{-9}C is placed at this point, what is the force experienced by the test charge?

Q 1.9: A system has two charges q_{A}=2.5\times 10^{-7}Cand q_{B}=-2.5\times 10^{-7} C located at points A: (0, 0, –15 cm) and B: (0,0, +15 cm), respectively. What are the total charge and electric dipole moment of the system?

Q 1.10: An electric dipole with dipole moment 4\times 10^{-9} Cm is aligned at 30^{\circ} with the direction of a uniform electric field of magnitude 5\times 10^{4}NC^{-1} . Calculate the magnitude of the torque acting on the dipole.

Q 1.11(a): A polythene piece rubbed with wool is found to have a negative charge of 3\times 10^{-7}. (a) Estimate the number of electrons transferred (from which to which?)

Q 1.11(b): A polythene piece rubbed with wool is found to have a negative charge of 3\times 10^{-7}C. Is there a transfer of mass from wool to polythene?

Q 1.12(a):  Two insulated charged copper spheres A and B have their centres separated by a distance of 50 cm. What is the mutual force of electrostatic repulsion if the charge on each is 6.5\times 10^{-7}C? The radii of A and B are negligible compared to the distance of separation.

Q 1.12(b): What is the force of repulsion if each sphere is charged double the above amount, and the distance between them is halved?

Q 1.13: Suppose the spheres A and B in Exercise 1.12 have identical sizes. A third sphere of the same size but uncharged is brought in contact with the first, then brought in contact with the second, and finally removed from both. What is the new force of repulsion between A and B?

Q 1.14: Figure  shows tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges. Which particle has the highest charge to mass ratio?

Q 1.15(a): Consider a uniform electric field E=3\times 10^{3}\ \widehat{i}\ N/C. (a) What is the flux of this field through a square of 10 cm on a side whose plane is parallel to the yz plane?

Q 1.15(b) Consider a uniform electric field E=3 \times 10^{3}\ \widehat{i}\ N/C .What is the flux through the same square if the normal to its plane makes a 60^{\circ} angle with the x-axis?

Q 1.16: What is the net flux of the uniform electric field of Exercise 1.15 through a cube of side 20 cm oriented so that its faces are parallel to the coordinate planes?

Q 1.17 (a) Careful measurement of the electric field at the surface of a black box indicates that the net outward flux through the surface of the box is 8.0 \times 10^{3}\frac{Nm^{2}}{C}. (a) What is the net charge inside the box?

Q 1.17 (b): Careful measurement of the electric field at the surface of a black box indicates that the net outward flux through the surface of the box is 8.0\times 10^{3}\frac{Nm^{2}}{C}.If the net outward flux through the surface of the box were zero, could you conclude that there were no charges inside the box? Why or Why not?

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