Physics Class 12 NCERT Solutions: Chapter 1 Electric Charges and Fields Part 8 (For CBSE, ICSE, IAS, NET, NRA 2022)

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

(A)

Q_26_A_Surface of the Conductor

(B)

Q_26_B_Curves Terminate at a Positive Charge

(C)

Q_26_C_Curves of the Positive Charges and Repel

(D)

Q_26_D_Curves of the Field Lines Should Not Interse …

(E)

Q_26_E_Curves Area of Fdield Lines

Answer:

(A) The field lines showed in (A) do not represent electrostatic field lines because field lines must be normal to the surface of the conductor.

(B) The field lines showed in (B) do not represent electrostatic field lines because the field lines cannot emerge from a negative charge and cannot terminate at a positive charge.

(C) The field lines showed in (C) represent electrostatic field lines. This is because the field lines emerge from the positive charges and repel each other.

(D) The field lines showed in (D) do not represent electrostatic field lines because the field lines should not intersect each other.

(E) The field lines showed in (E) do not represent electrostatic field lines because closed loops are not formed in the area between the field lines.

Q: 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 meter. What are the force and torque experienced by a system having a total dipole moment equal to in the negative z- direction?

Answer:

Dipole moment of the system,

Rate of increase of electric field per unit length,

Force (F) experienced by the system is given by the relation,

The force is in the negative z-direction i.e.. , opposite to the direction of electric field. Hence, the angle between electric field and dipole moment is . Torque is given by the relation,

Therefore, the torque experienced by the system is zero.