ExamGOAL
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MCQ Single Correct
MCQ Multiple Correct
Subjective
14

Consider two conducting spheres of radii $R_1$ and $R_2$ with $R_1>R_2$. If the two are at the same potential, the larger sphere has more charge than the smaller sphere. State whether the charge density of the smaller sphere is more or less than that of the larger one.

15

Do free electrons travel to region of higher potential or lower potential?

16

Can there be a potential difference between two adjacent conductors carrying the same charge?

17

Can the potential function have a maximum or minimum in free space?

18

A test charge $q$ is made to move in the electric field of a point charge $Q$ along two different closed paths [figure first path has sections along and perpendicular to lines of electric field. Second path is a rectangular loop of the same area as the first loop. How does the work done compare in the two cases?

19

Prove that a closed equipotential surface with no charge within itself must enclose an equipotential volume.

20

A capacitor has some dielectric between its plates and the capacitor is connected to a DC source. The battery is now disconnected and then the dielectric is removed . State whether the capacitance, the energy stored in it, electric field, charge stored and the voltage will increase, decrease or remain constant.

21

Prove that, if an insulated, uncharged conductor is placed near a charged conductor and no other conductors are present, the uncharged body must intermediate in potential between that of the charged body and that of infinity.

22

Calculate potential energy of a point charge $-q$ placed along the axis due to a charge $+Q$ uniformly distributed along a ring of radius $R$. Sketch PE, as a function of axial distance $z$ from the centre of the ring. Looking at graph, can you see what would happen if $-q$ is displaced slightly from the centre of the ring (along the axis)?

23

Calculate potential on the axis of a ring due to charge $Q$ uniformly distributed along the ring of radius $R$.

24

Find the equation of the equipotentials for an infinite cylinder of radius $r_0$ carrying charge of linear density $\lambda$.

25

Two point charges of magnitude $+q$ and $-q$ are placed at $(-d / 2,0,0)$ and $(d / 2,2,0)$, respectively. Find the equation of the equipotential surface where the potential is zero.

26

A parallel plate capacitor is filled by a dielectric whose relative permittivity varies with the applied voltage (U) as $\varepsilon=\alpha U$ where $a=2 \mathrm{~V}^{-1}$. A similar capacitor with no dielectric is charged to $U_0=78 \mathrm{~V}$. It is then connected to the uncharged capacitor with the dielectric. Find the final voltage on the capacitors.

27

A capacitor is made of two circular plates of radius $R$ each, separated by a distance $d \ll R$. The capacitor is connected to a constant voltage. A thin conducting disc of radius $r \ll R$ and thickness $t \ll r$ is placed at a centre of the bottom plate. Find the minimum voltage required to lift the disc if the mass of the disc is $m$.

28

(a) In a quark model of elementary particles, a neutron is made of one up quarks [charge $(2 / 3) e$ ] and two down quarks [charges - (1/3)e]. Assume that they have a triangle configuration with side length of the order of $10^{-15} \mathrm{~m}$. Calculate electrostatic potential energy of neutron and compare it with its mass 939 MeV .

(b) Repeat above exercise for a proton which is made of two up and one down quark.

29

Two metal spheres, one of radius $R$ and the other of radius $2 R$, both have same surface charge density $\sigma$. They are brought in contact and separated. What will be new surface charge densities on them?

30

In the circuit shown in figure, initially $K_1$ is closed and $K_2$ is open. What are the charges on each capacitors? Then $K_1$ was opened and $K_2$ was closed (order is important), what will be the charge on each capacitor now? $[C=1 \propto \mathrm{~F}]$

31

Calculate potential on the axis of a disc of radius $R$ due to a charge $Q$ uniformly distributed on its surface.

32

Two charges $q_1$ and $q_2$ are placed at $(0,0, d)$ and $(0,0,-d)$ respectively. Find locus of points where the potential is zero.

33

Two charges $-q$ each are separated by distance $2 d$. A third charge $+q$ is kept at mid-point 0 . Find potential energy of $+q$ as a function of small distance $x$ from 0 due to $-q$ charges. Sketch PE Vs $/ x$ and convince yourself that the charge at 0 is in an unstable equilibrium.