Will a penny be slightly more massive if it has a negative or a positive net cha

Question

Will a penny be slightly more massive if it has a negative or a positive net charge? (Think very small!!) (a) It will be just as massive either way. (b) More massive if negative. (c) More massive if positive. A charge conducting object is brought close to a neutral insulating object. Which of the following is true? (a) The objects will repel. (b) The objects will attract. (c) Nothing will happen, no attraction, no repulsion. (d) The objects will repel as long as the charge on the conducting object is negative. (e) The objects will attract as long as the charge on the conducting object is positive. An object has a net electric charge of +3.2 mu C. How many electrons would need to be added to make it electrically neutral? (a) 2.0 times 10^13 (b) 2.0 times 10^ (c) 3.2 times 10^-4 (d) 3.2 times 10^6 (e) 5.0 times 10^-14 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

Problem 3) Option (b): More massive if move towards negative charge.

The penny will be slightly more massive with a negative charge, because then it will have more electrons than when neutral. If it were positively charged, it would be slightly lighter because of missing electrons.

Problem 4) Option (c): Nothing will happen, neither attraction nor repulsion.

Since the object is insulting, there will be no induction of charge at its outer surface when an object brought close to it, so, nothing will happen.

Problem 6) Option (a): 2 x 1013

Using relation, Q = n e (n is no. of electrons, e is charge of electron)

So, no. of electons, n = Q/e = (3.2 x 10-6) / (1.6 x 10-19) = 2 x 1013

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