Electric field and charges -DPP4(ISC)

The unit of electric field is not equivalent to

• $\frac{N}{C}$

• $\frac{J}{C}$

• $\frac{V}{m}$

• $\frac{J}{C-m}$

A flat circular disc has a charge uniformly distributed on the disc. A charge is thrown with kinetic energy towards the disc along its normal axis. The charge will

• Hit the disc at the centre

• Return back along its path after touching the disc

• Return back along its path without touching the disc

• Any of the above three situations is possible depending on the magnitude of E

A mass m=20g has a charge q=3.0mC . It moves with a velocity of 20m/s and enters a region of electric field of 80N/C in the same direction as the velocity of the mass. The velocity of the mass after 3 seconds in this region is

• 80 m/s

• 56m/s

• 44m/s

• 40m/s

Two insulated charged conducting spheres of radii 20cm and 15cm respectively and having an equal charge of 10C are connected by a copper wire and then they are separated. Then

• Both the spheres will have the same charge of 10C

• Surface charge density on the 20cm sphere will be greater than that on the 15cm sphere

• Surface charge density on the 15cm sphere will be greater than that on the 20cm sphere

• Surface charge density on the two spheres will be equal

Four charges are placed on corners of a square as shown in figure having side of 5cm. If Q is one microcoulomb, then electric field intensity at centre will be

• $1.02\times10^{7\ }\ \frac{N}{C\ }upwards\$

• $2.04\times10^{7\ }\ \frac{N}{C\ }downwards\$

• $2.04\times10^{7\ }\ \frac{N}{C\ }upwards\$

• $1.02\times10^{7\ }\ \frac{N}{C\ }downwards\$

A cube of side has a charge at each of its vertices. The electric field due to this charge distribution at the centre of this cube will be

• $\frac{q}{b^2}$

• $\frac{q}{2b^2}$

• $\frac{32q}{b^2}$

• zero

Consider the points lying on a straight line joining two fixed opposite charges. Between the charges there is

• No point where electric field is zero

• Only one point where electric field is zero

• No point where potential is zero

• Only one point where potential is zero

Figures below show regular hexagons, with charges at the vertices. In which of the following cases the electric field at the centre is not zero

• 1

• 2

• 3

• 4

An electric dipole in a uniform electric field experiences (When it is placed at an angle $\theta$   with the field)

• Force and torque both

• Force but no torque

• Torque but no force

• No force and no torque

A molecule with a dipole moment p is placed in an electric field of strength E. Initially the dipole is aligned parallel to the field. If the dipole is to be rotated to be anti-parallel to the field, the work required to be done by an external agency is

• – 2pE

• – pE

• pE

• 2pE