Ls 2 - Electrostatic Potential and Capacitance

Notes

Questions

  1. A regular hexagon of side 10cm has a charge 5uC at each of its vertices . Calculate the potential at the centre of the hexagon.

  2. As in the figure, if a capacitor of capacitance 'C' is charged by connecting it with resistance 'R', then energy given by the battery will be a) 1/2CV^2 b) less than 1/2CV^2 c) CV^2 d) more than CV^2

  3. There is a uniform electrostatic field in a region. The potential at various points on a small sphere centred at P, in the region, is found to vary between in the limits 589.0 V to 589.8 V. What is the potential at a point on the sphere whose radius vector makes an angle of 60 deg with the direction of the field? (A) 589.5 V (B) 589.2 V (C) 589.4 V (D) 589.6 V

Worksheet

Electric Potential - PYQs.pdf

Notes

Formula Cheat sheet

  1. Electric potential: V=WqV = \frac{W}{q}

  2. W = q(VAVB) where VA>VBq (V_A-V_B) \ where \ V_A > V_B

  3. E = dVdl- \frac{dV}{dl} (relation between electric intensity and potential)

  4. Electric potential at point due to isolated point charge, V=14πεoqrV = \frac{1}{4πε_o} \frac{q}{r}

  5. Electric potential at point due to an electric dipole, V=14πεop cosθr2V = \frac{1}{4πε_o} \frac{p \ cos \theta}{r^2}

  6. Potential energy of system of charges in the absence of external electric field - is due to superposition principle which is very similar to addition of vectors

  7. Potential energy of system of charges in the presence of external electric field

    1. Single charge: - U = Vq

    2. Two charges: -U=V(r1)q1+V(r2)q2+14πεoq1q2r12U= V(r_1)q_1+ V(r_2)q_2+ \frac{1}{4πε_o} \frac{q_1q_2}{r_{12}}

    3. Electric dipole: U=pE(cosθocosθ1)U =- pE (cos θ_o-cos θ_1)

  8. C=QVC= \frac{Q}{V}

  9. Capacitance of parallel plate capacitor: V=εrεoAdV = \frac{ε_rε_oA}{d}

  10. Energy stored in capacitor, E=12CV2E = \frac{1}{2}CV^2

  11. Series combination of capacitors, -= +1+- C1C2

    1. For two capacitors connected in series, Cs = +C2

    2. For n identical capacitors connected in series, Cn =-

  12. Parallel combination of capacitors, CpC_p = C1 + C2+ C3

    1. For two Capacitors connected in parallel, CpC_p = C1+ C2

    2. For n identical capacitors connected in parallel, CpC_p = nC

  13. Dielectric polarization P = x E where x is electric susceptibility

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