If a copper wire is stretched to make its radius decrease by 0.1%, then the percentage increase in resistance is approximately

A thin conducting ring of radius R is given a charge +Q. The electric field at the centre O of the ring due the charge on the part AKB of the ring is E. The electric field at the centre due to the charge on the part ACDB of the ring is ?

Three point charges +q, −q and +q are placed at points (x = 0, y = a, z = 0),(x = 0, y = 0, z = 0) and (x = a, y = 0, z = 0) respectively. The magnitude and direction of the electric dipole moment vector of this charge assembly are ?

Two steel wires having the same length are suspended from a ceiling under the same load. If the ratio of their energy stored per unit volume is 1:4, the ratio of their diameters is

The electric intensity due to a dipole of length 10 cm and having a charge of 500μC, at a point on the axis at a distance 20 cm from one of the charges in air, is ?

If a dipole of dipole moment p is placed in a uniform electric field E, then torque acting on it is given by ?

If a dipole of dipole moment \( \vec{p} \) is placed in a uniform electric field \( \vec{E} \), then the torque acting on it is given by ?

<p>(a) \( \vec{\tau} = \vec{p} \cdot \vec{E} \)</p>

<p>(b) \( \vec{\tau} = \vec{p} \times \vec{E} \)</p>

<p>(c) \( \vec{\tau} = \vec{p} + \vec{E} \)</p>

<p>(d) \( \vec{\tau} = \vec{p} - \vec{E} \)</p>

Answer :  <p>(b) \( \vec{\tau} = \vec{p} \times \vec{E} \)</p>

A semi-circular arc of radius ’ a ’ is charged uniformly and the charge per unit length is λ. The electric field at the centre of this arc is ?

A hollow insulated conduction sphere is given a positive charge of 10μC. What will be the electric field at the centre of the sphere if its radius is 2 metres ?

A point Q lies on the perpendicular bisector of an electrical dipole of dipole moment p. If the distance of Q from the dipole is r (much larger than the size of the dipole), then the electric field at Q is proportional to ?

From a point charge, there is a fixed point A. At A, there is an electric field of 500 V/m and potential difference of 3000 V. Distance between point charge and A will be ?

An electric dipole, consisting of two opposite charges of 2 × 10−6C each separated by a distance 3 cm is placed in an electric field of 2 × 105 N/C. Torque acting on the dipole is ?

There is an electric field E in X-direction. If the work done on moving a charge of 0.2C through a distance of 2 m along a line making an angle 60◦ with x-axis is 4 J, then what is the value of E ?

Two point charges A and B, having charges +Q and −Q respectively, are placed at certain distance apart and force acting between them is F. If 25% charge of A is transferred to B, then force between the charges becomes: ?

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

Suppose the charge of a proton and an electron differ slightly. One of them is - e, the other is (e + ∆e). If the net of electrostatic force and gravitational force between two hydrogen atoms placed at a distance d (much greater than atomic size) apart is zero, then ∆e is of the order of [Given mass of hydrogen mh = 1.67 × 10−27 kg ] ?

If the work done is stretching a wire by 1 mm is 2 J, the work necessary for stretching another wire of same material but with double the radius of cross section and half the length by 1 mm is

Two identical charged spheres suspended from a common point by two massless strings of lengths l, are initially at a distance d(d ≪ l) apart because of their mutual repulsion. The charges begin to leak from both the spheres at a constant rate. As a result, the spheres approach each other with a velocity v. Then v varies as a function of the distance x between the spheres, as: ?

Two pith balls carrying equal charges are suspended from a common point by strings of equal length. The equilibrium separation between them is r. Now the strings are rigidly clamped at half the height. The equilibrium separation between the balls now become ?

A charge ’ q ’ is placed at the centre of the line joining two equal charges ’ Q ’. The system of the three charges will be in equilibrium if ’ q ’ is equal to ?

Two metallic spheres of radii 1 cm and 3 cm are given charges of −1 × $10^{−2}$C and 5 × $10^{−2}$C, respectively. If these are connected by a conducting wire, the final charge on the bigger sphere is ?