Question

( begin{array}{rl}mid 4, quad F=q & E H operatorname{er} e ; quad F=3.2 times 10^{-13} & N E=5 times 10^{5} & N / C E=frac{F}{E}= & frac{3.2 times 10^{-13}}{5 times 10^{5}} = & 0.64 times 10^{-18} = & 6.4 times 10^{-19} mathrm{C}end{array} )

# 12. There are three points A, B and C at the corners of an equilateral triangle. There is a point-charge of + 0.100 uc at A. What will be the intensity of electric field at the mid-point between B and C, if the side of the triangle is 10-0 cm. 13. Electric charges + 1000 uC are placed at points A and B respectively at a distance of 2 m from Ans. 1.20 x 10' N/C. each other. Calculate the electric fields at (i) mid-point of the line AB, and (ii) at a point at equal distances of 4 m from each charge. Ans. (i) 1.8 x 10' NC, along AB ; (ii) 2.8 x 10°NC, parallel to AB. 14. If an oil drop of weight 3.2 x 10'' N is balanced in an electric field of 5 x 10 NC, find the charge on the drop. Ans. 6.4 x 10-9C. 15. A charged drop of oil of radius 2.76 um and density 920 kg m is held stationary in a vertically downward electric field of 1.65 x 10°NC (1) Find the magnitude and sign of the charge on the drop. (ii) If the drop captures two electrons in the same electric field, what would be its acceleration ? Ignore viscous drag. Ans. (i) -4.8 x 10-19 C, (ii) 6.5 ms 2. 16. Two charges, one + 5 uC and other - 5 uC are placed 1 mm apart. Calculate the dipole moment. Ans. 5 x 10°C m.

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