Q.No.12.8: - Is it true that Gauss’s Law states that the total number of lines of forces crossing any closed surface in the outward direction is proportional to the net positive charge enclosed within surface.

Q.No.12.8: - Is it true that Gauss’s Law states that the total number of lines of forces crossing any closed surface in the outward direction is proportional to the net positive charge enclosed within surface.

Ans: - Yes this is true. According to Gauss’s law the total no of electric field lines coming out of a closed surface is proportional to the total no of charges present in that closed surface.

Mathematically,

The above statement is true.

Q.No.12.6: - If a point charge q of mass m is released in a non-uniform electric field, will it make a rectilinear motion?

Q.No.12.6: - If a point charge q of mass m is released in a non-uniform electric field, will it make a rectilinear motion?

Ans: - A rectilinear motion means a motion along a straight line. If a point charge q of mass m is placed at any point in the non-uniform electric field. Suppose this field is caused by a positive point charge then the charge will experience a repulsive force (as the force will exert on the charge along the line joining the two charges) and the charge will follow a straight path which makes a rectilinear motion.

Q.No.12.4: - Describe the force or forces on a positive point charge when placed between parallel plates. (a) with similar and equal charges. (b) with opposite and equal charges.

Q.No.12.4: - Describe the force or forces on a positive point charge when placed between parallel plates.

(a)    with similar and equal charges.

(b)    with opposite and equal charges.

Ans: - (a). If the plates have similar and equal charge in magnitude and we place the positive point charge between such plates then both the plates want to repel this positive point charge with same Coulomb’s force. The net force on the charge will be zero.

          (b). If the plates have similar and opposite charge in magnitude and we place the positive point charge between such plates then positive plate will repel the positive charge and exert a force F₁ while negative plate will attract it and exert an attractive force F₂.

          Net force        =           F        =      F₁   +     F₂  

Q.No.12.3: - How can you identify that which plate of a capacitor is positively charged?

Q.No.12.3: - How can you identify that which plate of a capacitor is positively charged?

Ans: - For this purpose we can use Gold Leaf Electroscope (GLE). We bring the disc of a positively charged electroscope close to the plate of the capacitor. If the divergence of the gold leaf increases, then the plate is positively charged and if the divergence in the leaf decreases, then the plate is negatively charged.

                                                  Or

Rub together a plastic rod and a piece of fur, both initially uncharged, the rod acquires a negative charge (since it takes electrons from the fur) and the fur acquires a positively charge of the same magnitude ( since it has lost as many electrons as the rod has gained). Now bring the plastic rod to one of the capacitors plate is there is a repulsion between the plastic rod and the capaticor’s plate then it means that the plate is negatively charged and the other has positive charge and vice versa.