# NCERT Exemplar Solutions for CBSE Class 12 Physics, Chapter 2 (Part III)

Jul 21, 2017 09:15 IST

NCERT Exemplar solutions for Class 12 Physics, Chapter 2 Electrostatic Potential and Capacitance are available here. Here, you will find solutions to very short answer type questions (i.e., question number 2.14 to question number 2.18). Solutions of question number 2.1 to 2.13 are available in Part I and Part II. Solutions of other questions will be available in further parts. These questions are important for CBSE Class 12 Physics board exam and other competitive exams like JEE Main, NEET etc.

The solutions are given below:

Question 2.14: Consider two conducting spheres of radii R1 and R2 with R1 > R2. 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.

Solution 2.14:

Potential at a point due to a charged sphere is given by, V = kQ/R or V = Q/4πεoR

According to the question, V1 = V2

Q1/4πεoR1 = Q2/4πεoR2

Q1/Q2 = R1/R2 …(i)

Here, R1 > R2Q1 > Q2

In charged sphere surface charge densities is given by, σ = Q/4πεoR2

Now,

σ1 = Q1/4πεoR12 and σ2 = Q2/4πεoR22

σ12 = (Q2/R22) (R12/Q1)

From equation …(i) σ21 = R1/R2

As, R1 > R2, therefore, σ2 < σ1.

It means charge density of smaller sphere is more than charge density of larger sphere.

CBSE Class 12 Physics Syllabus 2017 – 2018

Question 2.15: Do free electrons travel to region of higher potential or lower potential?

Solution 2.15:

In a uniform electric field, free electrons move opposite to the direction of electric field.

As the electric field is always direct from higher potential to lower travel so, electrons move from lower potential to higher potential.

Question 2.16: Can there be a potential difference between two adjacent conductors carrying the same charge?

Solution 2.16: In a uniform electric field, free electrons move opposite to the direction of electric field.

As the electric field is always direct from higher potential to lower travel so, electrons move from lower potential to higher potential.

Question 2.17: Can the potential function have a maximum or minimum in free space?

Solution 2.17:

No, the potential function cannot have a maximum or minimum in free space.

Question 2.18: A test charge q is made to move in the electric field of a point charge Q along two different closed paths (as shown in figure given below). 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?

Solution 2.18:

We know that, electric field is conservative; hence, work done will be zero in both the cases.

NCERT Solutions for Class 12 Physics, Chapter 2 Electrostatic Potential and Capacitance

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