Three point charges are located along the x-axis, as illustrated. The charge in

Question

Three point charges are located along the x-axis, as illustrated. The charge in the middle has a mass of 4.0 times 10^-9 kg. Calculate the magnitude and the direction of the acceleration of the charge in the middle when it is allowed to move, if the others remain fixed in place. (a) 2 times 10^5 m/s^2, to the right (b) 1 times 10^5 m/s^2, to the left (c) 7 times 10^4 m/s^2, to the right (d) 3 times 10^5 m/s^2, to the left (e) 4 times 10^6 m/s^2, to the right Four point charges are fixed at the corners of a square, as illustrated. Which of the arrows shows the correct direction of the net electric force that acts on the charge in the upper right corner, due to the presence of the other three? (a) A (b) B (c) C (d) D (e) None - the net force is zero Consider the two point-charges shown in this diagram. They together produce an electric field at point P, in the direction shown. Which of the following is true about charge Q? (a) Q is positive, with |Q| = |q| (b) Q is positive, with |Q| > |q| (c) Q is negative, with |Q| = |q| (d) Q is negative, with |Q| > |q| If the lower charge were negative instead, is there any way the field could have the direction shown in the figure? (a) Yes, if Q is positive. (b) Yes, if Q is negative. (c) No, there is no way.

Explanation / Answer

11 ) Force on charge -1.2 uC by 1.5uC = kq1q2 / r^2

= 9*10^9*1.5*1.2*10^-12 / 4^2

= 1.1025*10^-3 N ( to the left)

Force on charge -1.2uC by 2 uC = 9*10^9 * 1.2*2*10^-12 / 6^2

= 6*10^-4 N ( to the right)

net force on charge -1.2 uC = (1.1025*10^-3 - 6*10^-4) = 4.125*10^-4 N

acceleration = F/m = 4.125*10^-4 / 4*10^-9

= 1.03*10^5 m/s2

so option b) 1.03*10^5 m/s2 to the left is the correct answer

27) negative charge as electric field towards it

so option d) Q is negative , with [Q] > [q]

28) is q is negative , EF will be in downward direction due to q

so Net EF will be in upward direction , only when Q is negative and greater in magnitude

So, option b)Yes if, Q is negative

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