IIT JEE , AIEEE Forum - Physics , Electricity - Simple assertion-reason-2...

Ronaldooo

Assertion-When a body is connected to earth,it becomes electrically neutral
Reason-Electric potential of earth is 0 so the electric potential of the body should also become 0.

Assertion-Energy stored in capacitor is less than the energy drawn from the battery during the charging of capacitor.
Reason-Some of the energy is converted into heat.

computer001

1st q
well earth has infinite capacitance
so chrg from other body will flow into it
so A i suppose
2)
A- energy drwan from battery = CV^2
energy stored in cap=1/2CV^2
energy lost to heating=1/2CV^2

Ronaldooo

Then,why,sometimes during start of thunderstorms,our hair stands...somewhat like its getting attracted to something near it...at that time,we still are connnected to the ground.So,we should be electrically neutral.Then,why the standing happens???

computer001

tht mustb sumtin lik

a dipole is created in our body due to separation of chrgs due to thunderstorms electric field

Ronaldooo

Can anyone explain the 1st one??

neeraj_agarwal_1990

whenever 2 bodies are connected via a connecting wire, their potential becomes equal...since the potential of earth is taken to be 0....any body which is earthed has its potential equal to 0...

but 0 potential doesn't mean zero charge....

u my consider 3 concentric shells with different charges....connect one of them to earth and then try to find the NEW charge on it using its potential to be 0....u'll not get the charge as 0!

neeraj_agarwal_1990

so answer is D....

ayshwarya

earth posses huge potential so either v add or remove a charge it does not effect its potential hence d potential is cpnsidered as 0

ayshwarya

hence by connecting a body to earth no charge is flown frm earth hence d body remains electricaly neitral hence ans is ( i )fr 1st question

ayshwarya

plz do vote me if im rite

SCIENTIST135

ANS IS A IN BOTH QUESTIONS.

IF ONLY ONE BODY IS PRESENT, THEN IT WIIL CONTAIN ZERO CHARGE IF IT IS IN CONTACT WITH EARTH. NEERAJ IS GIVING EXAMPLE OF SPHRICAL CAPACITANCES. THIS IS NOT THE CASE TAKEN WITH QUES.

A BODY CANNOT ACT ITSELF AS A CAPACITOR.

neeraj_agarwal_1990

ya thats true....it will become electrically neutral if the body is isolated...

thevyzz

1) Ans is B. The reason why the potential becomes zero is that we assume earth to have infinite capacitance. The potential of earth never changes(This is given in the assertion). Imagine two symmetrical bodies with potentials 10V and 0V. Connect them, now the potential of the 10V body doesn;t change to zero. It happens only when it is connected to the earth( because of infinite capacitance)as the potential of earth never changes(This is not given in the reason)

srini

Hey,

ya we CONSIDER the earths potential as zero because not much change is observed when charges are passed to the earth

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