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Monday 14 October 2013

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.

Q.No.12.2: - Suppose that you follow an electric field line due to a positive point charge. Do electric field and the potential increase or decrease?


Q.No.12.2: - Suppose that you follow an electric field line due to a positive point charge. Do electric field and the potential increase or decrease?
Ans: - If we follow an electric field line due to a positive point charge then we will move away from the positive point charge because the electric field produced by a positive charge is away from charge. Electric field and electric potential both inversely dependent on the distance from the charge to the selected point (say P). So as we follow the positive charge then we will move away from the charge. The formula of electric field  and electric potential is
                    E    =    qq′/4πЄ0r2      and       V     =     q/4πЄ0r    
So as we follow then electric field and electric potential will decrease.

Q.No.12.1: - The potential is constant throughout a given region of space. Is the electrical field zero or nonzero in this region? Explain.


Q.No.12.1: - The potential is constant throughout a given region of space. Is the electrical field zero or nonzero in this region? Explain.
Ans: - The electric field has a relation with change in electrical potential which is
                                                E   =   -ΔV/Δr
In this case ΔV is the change in electrical potential and if the change in potential is zero then E will be zero and ΔV will be zero only when there is no change in electrical potential. This is given in question that electrical potential is constant throughout the given region of space hence, E = 0 when ΔV=0
Mathematically,
                                  E   =   -ΔV/Δr   =    -0/Δr    =   0