Electric Charges and Fields

A conducting sphere of radius R = 20 cm is given by a charge Q = 16μC. What is E at centre?

• 3.6×10⁶ N/C

• 1.8×10⁶ N/C

• Zero

• 0.9×10⁶ N/C

Two charged spheres separated by a distance d exert some force (F) on each other. If they are immersed in a liquid of dielectric constant 4, then what is the force exerted, if all other conditions are same ?

• 2F

• 4F

• $\frac{\mathrm{F}}{2}$

• $\frac{\mathrm{F}}{4}$

In a discharge tube ionization of enclosed gas is produced due to collisions between

• positive ions and neutral atoms/molecules

• negative electrons and neutral atoms/molecules

• photons and neutral atoms/molecules

• photons and neutral atoms/molecules

A charge q is located at the centre of a cube. The electric flux through any face is

• $\frac{4\mathrm{\pi q}}{6 \left(4{\mathrm{\pi \epsilon }}_0\right)}$

• $\frac{\mathrm{\pi q}}{6\left(4{\mathrm{\pi \epsilon }}_0\right)}$

• $\frac{\mathrm{q}}{6\left(4{\mathrm{\pi \epsilon }}_0\right)}$

• $\frac{2\mathrm{\pi q}}{6\left(4{\mathrm{\pi \epsilon }}_0\right)}$

Number of extra electrons in a body of charge -80$\mathrm{\mu }$C, is

• 80 × 10¹⁵

• 80 × 10⁻¹⁵

• 5 × 10¹⁴

• 1.28 × 10⁻¹⁷

The figure shows three points A, B and C in a region of a uniform electric field $\overrightarrow{\mathrm{E}}$. The line AB is perpendicular and BC is parallel to the field lines. Then which of the following holds good?

• V_A = V_B = V_C

• V_A = V_B > V_C

• V_A = V_B < V_C

• V_A > V_B = V_C

Two spheres of radii R₁ and R₂ respectively are charged and joined by a wire. The ratio of the electric field of spheres is :

• $\frac{{\mathrm{R}}_2^2}{{\mathrm{R}}_1^2}$

• $\frac{{\mathrm{R}}_1^2}{{\mathrm{R}}_2^2}$

• $\frac{{\mathrm{R}}_2}{{\mathrm{R}}_1}$

• $\frac{{\mathrm{R}}_1}{{\mathrm{R}}_2}$

If an insulated non-conducting sphere of radius R has charge density ρ. The electric field at a distance r from the centre of sphere (r > R) will be

• $\frac{\mathrm{\rho } \mathrm{R}}{3{\mathrm{\epsilon }}_{\mathrm{o}}}$

• $\frac{\mathrm{\rho } \mathrm{r}}{{\mathrm{\epsilon }}_{\mathrm{o}}}$

• $\frac{\mathrm{\rho } \mathrm{r}}{3 {\mathrm{\epsilon }}_{\mathrm{o}}}$

• $\frac{3 \mathrm{\rho } \mathrm{R}}{{\mathrm{\epsilon }}_{\mathrm{o}}}$

Two parallel large thin metal sheets have equal surface charge densities ( σ = 26.4 × 10^-12 C/m² ) of opposite signs. The electric field between these sheets is

• 1.5 N/C

• 1.5 × 10^-10 N/C

• 3 N/C

• 3 × 10^-10 N/C 

The spatial distribution of the electric field due to two charges (A, B) is shown in figure. Which one of the following statements is correct?

• A is +ve and +B is -ve and $\left|\mathrm{A}\right| > \left|\mathrm{B}\right|$

• A is $-$ve and B is +ve; $\left|\mathrm{A}\right| = \left|\mathrm{B}\right|$

• both are +ve but A > B

• both are $-$ve but A > B