The inward and outward electric flux from a closed surface are respectively 8 x 10³ and 4 x 10³ units. Then the net charge inside the closed surface is

• − 4 × 10³ coulomb

• 4 × 10³ coulomb

• $\frac{- 4 \times {10}^3}{{\mathrm{\epsilon }}_0} \mathrm{coulomb}$

• − 4 × 10³ ε₀ coulomb

In the circuit as shown in the figure, the effective capacitance between A and B is

• 2μ

• 2μ

• 8μ

• 4μ

Capacitance of a parallel plate capacitor becomes $\frac{4}{3}$ times its original value, if a dielectric slab of thickness $\mathrm{t} = \frac{\mathrm{d}}{2}$ is inserted between the plates [d is the separation between the plates]. The dielectric constant of the slab is

• 4

• 8

• 2

• 6

A charged particle of mass m and charge q is released from rest in an uniform electric field E neglecting the effect of gravity, the kinetic energy of the charged particle after 't' second is

• $\frac{2{\mathrm{E}}^2{\mathrm{t}}^2}{\mathrm{mq}}$

• $\frac{{\mathrm{Eq}}^2\mathrm{m}}{2{\mathrm{t}}^2}$

• $\frac{\mathrm{Eqm}}{\mathrm{t}}$

• $\frac{{\mathrm{E}}^2{\mathrm{q}}^2{\mathrm{t}}^2}{2\mathrm{m}}$

Two wires of the same dimensions but resistivities ρ₁ and ρ₂ are connected in series. The equivalent resistivity of the combination is

• $\frac{{\mathrm{\rho }}_1 + {\mathrm{\rho }}_2}{2}$

• ρ₁ + ρ₂

• 2 (ρ₁ + ρ₂)

• $\sqrt{{\mathrm{\rho }}_1 {\mathrm{\rho }}_2}$

I£ a 30V, 90W bulb is to be worked in 120V line, the resistance to be connected in series with the bulb is

• 20 Ω

• 10 Ω

• 40 Ω

• 30 Ω

The potential difference between the terminals of a cell in open circuit is 2.2 volt with resistance of 5 ohm across the terminals of a cell, the terminal potential difference is 1.8 volt. The internal resistance of the cell is

• $\frac{9}{10} \mathrm{ohm}$

• $\frac{10}{9} \mathrm{ohm}$

• $\frac{7}{12} \mathrm{ohm}$

• $\frac{12}{7} \mathrm{ohm}$

28.

Thirteen resistances each of resistance R ohm are connected in the circuit as shown in the figure. The effective resistance between A and B is

                    

• $\frac{4\mathrm{R}}{3} \mathrm{\Omega }$

• 2R Ω

• R Ω

• $\frac{2\mathrm{R}}{3} \mathrm{\Omega }$

A group of N cells whose emf varies directly with the internal resistance as per the equation E_N = 1.5 r_N are connected as shown in the figure above. The current I in the circuit is

• 5.1 A

• 0.51 A

• 1.5 A

• 0.15 A

The temperature coefficient of resistance of a wire is 0.00125/°C. Its resistance is 1 ohm at 300 K. Its resistance will be 2 ohm at

• 1127 K

• 1400 K

• 1154 K

• 1100 K