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# NCERT Solutions class 12 physics Electric Charges and Field Part 2

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## NCERT Class 12 Physics Chapter-wise Solutions

• 1 – Electric Charges and Fields
• 2 – Electrostatic Potential and Capacitance
• 3 – Current Electricity
• 4 – Moving Charges and Magnetism
• 5 – Magnetism and Matter
• 6 – Electromagnetic Induction
• 7 – Alternating Current
• 8 – Electromagnetic Waves
• 9 – Ray Optics and Optical Instruments
• 10 – Wave Optics
• 11 – Dual Nature of Radiation and Matter
• 12 – Atoms
• 13 – Nuclei
• 14 – Semiconductor Electronic: Material, Devices and Simple Circuits
• 15 – Communication Systems

## CHAPTER 1 ELECTRIC CHARGES AND FIELDS

• 1.1 Introduction
• 1.2 Electric Charges
• 1.3 Conductors and Insulators
• 1.4 Charging by Induction
• 1.5 Basic Properties of Electric Charge
• 1.6 Coulomb’s Law
• 1.7 Forces between Multiple Charges
• 1.8 Electric Field
• 1.9 Electric Field Lines
• 1.10 Electric Flux
• 1.11 Electric Dipole
• 1.12 Dipole in a Uniform External Field
• 1.13 Continuous Charge Distribution
• 1.14 Gauss’s Law
• 1.15 Application of Gauss’s Law

## NCERT Solutions class 12 physics Electric Charges and Field Part 2

18: A point charge +10  is a distance 5 cm directly above the centre of a square of side 10 cm, as shown in Fig. 1.34. What is the magnitude of the electric flux through the square? (Hint: Think of the square as one face of a cube with edge 10 cm.)

19: A point charge of 2.0  is at the centre of a cubic Gaussian surface 9.0 cm on edge. What is the net electric flux through the surface?

20: A point charge causes an electric flux of –  to pass through a spherical Gaussian surface of 10.0 cm radius centered on the charge. (a) If the radius of the Gaussian surface were doubled, how much flux would pass through the surface? (b) What is the value of the point charge?

21: A conducting sphere of radius 10 cm has an unknown charge. If the electric field 20 cm from the centre of the sphere is  and points radially inward, what is the net charge on the sphere?

22: A uniformly charged conducting sphere of 2.4 m diameter has a surface charge density of 80.0  /m2. (a) Find the charge on the sphere. (b) What is the total electric flux leaving the surface of the sphere?

23: An infinite line charge produces a field of  at a distance of 2 cm. Calculate the linear charge density.

24: Two large, thin metal plates are parallel and close to each other. On their inner faces, the plates have surface charge densities of opposite signs and of magnitude   What is E: (a) in the outer region of the first plate, (b) in the outer region of the second plate, and (c) between the plates?

25: An oil drop of 12 excess electrons is held stationary under a constant electric field of  in Millikan’s oil drop experiment. The density of the oil is 1.26 g cm-3. Estimate the radius of the drop.

26: Which among the curves shown in Fig. 1.35 cannot possibly represent electrostatic field lines?

(a)

(b)

(c)

(d)

(e)

27: In a certain region of space, electric field is along the z-direction throughout. The magnitude of electric field is, however, not constant but increases uniformly along the positive z-direction, at the rate of  per metre. What are the force and torque experienced by a system having a total dipole moment equal to  Cm in the negative z-direction?

28: (a) A conductor A with a cavity as shown in Fig. 1.36(a) is given a charge Q. Show that the entire charge must appear on the outer surface of the conductor. (b) Another conductor B with charge q is inserted into the cavity keeping B insulated from A. Show that the total charge on the outside surface of A is Q + q [Fig. 1.36(b)]. (c) A sensitive instrument is to be shielded from the strong electrostatic fields in its environment. Suggest a possible way.

29: A hollow charged conductor has a tiny hole cut into its surface. Show that the electric field in the hole is , where is the unit vector in the outward normal direction, and  is the surface charge density near the hole.

30: Obtain the formula for the electric field due to a long thin wire of uniform linear charge density without using Gauss’s law. [Hint: Use Coulomb’s law directly and evaluate the necessary  integral.]

31: It is now believed that protons and neutrons (which constitute nuclei of ordinary matter) are themselves built out of more elementary units called quarks. A proton and a neutron consist of three quarks each. Two types of quarks, the so called ‘up’ quark (denoted by u) of charge e, and the ‘down’ quark (denoted by d) of charge (-1/3) e, together with electrons build up ordinary matter. (Quarks of other types have also been found which give rise to different unusual varieties of matter.) Suggest a possible quark composition of a proton and neutron.

32: (a) Consider an arbitrary electrostatic field configuration. A small test charge is placed at a null point (i.e., where E = 0) of the configuration. Show that the equilibrium of the test charge is necessarily unstable.

(b) Verify this result for the simple configuration of two charges of the same magnitude and sign placed a certain distance apart.

33: A particle of mass m and charge ( – q) enters the region between the two charged plates initially moving along x-axis with speed vx (like particle 1 in Fig. 1.33). The length of plate is L and an uniform electric field E is maintained between the plates. Show that the vertical deflection of the particle at the far edge of the plate is

Compare this motion with motion of a projectile in gravitational field discussed in Section 4.10 of Class XI Textbook of Physics.

34: Suppose that the particle in Exercise in 1.33 is an electron projected with velocity  . If E between the plates separated by 0.5 cm is , where will the electron strike the upper plate? (| e | = .)

## NCERT Solutions for Class 12 Physics

NCERT Solutions Class 12 Physics PDF (Download) Free from myCBSEguide app and myCBSEguide website. Ncert solution class 12 physics includes text book solutions from both part 1 and part 2. NCERT Solutions for CBSE Class 12 Physics have total 20 chapters. 12 Physics NCERT Solutions in PDF for free Download on our website. Ncert physics class 12 solutions PDF and physics ncert class 12 PDF solutions with latest modifications and as per the latest CBSE syllabus are only available in myCBSEguide

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