FIVE VERY- BASIC and CONCEPTUALl Questions for IIT JEE from ELECTROSTATICS from ARIHANT :

I've read in the NCERT textbook that electric fields are very real physical quantities and not just mathematical constructs . Otherwise EM waves wouldn't exist.

But gravitational fields were just invented by us to make studying gravity easier.

I think thats what they meant in question 5

of cource my friend electric field is a physical quantity. it will be very unwise to that it isnt. people in the 1990s subjected to that. but coming to the question.

we have given that the body is dimensionless. may i take the liberty to tell you dat and dimensionless body will either have zero mass or infinite mass (according to Einstein's special theory of relativity). but if you see logicall i dimentionless quantity cannot have mass. we have not defined it in any of our courses. so gravitation field moves out of question.

while a charge is considered it is well said that it is dimentionless and the mass f the cahrge is neglegted in our calculation. therefore we can presumebaly say within the limits of our syllabus that electric field is the answer.

in reality this answer may also be wrong. but we cannot dweell into higher prospects of physcs with such little amount of information that we have at this stage. thank you

let me explain you the same concept with a slightly different question. suppose on an inverted hemisphere a ball is kept as shown in the figure.

we define this as unstable equilibrium, it is one of the most famous examples of this. but what if we slightly displace it in the upward direction it will bounce back slowly on the midpoint and remain there. so this can also be argued as a case of stable equilibrum. but it is not so. so in these cases we see the potential energy. it will be maximum as compared to any other point on the hemisphere.

in the similar way if yew caclucate the potential enrgy by taking some rough measurement of the charge and distance you will see that it is highest at that point. this will proove that it is in unstable equilibrium. thank you

Same explanation for 3 [4][3][6]

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yeah thats right, but U need to consider all the possible ways, b4 deciding it is stable.

But NEway, wen U R moving it in the equitorial plane, the potential remains same...... U can check for stability of equilibrium only by slightly changing the potential..........

So, mere moving of charge without change in potential doesnt give NE idea of stability of eqilibrium!!

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but what if the charge is moved along the perpendicular bisector ..then equilibrium is STABLE rt..what explanation do u have for that ..pls ?[7]