Hanging from threads are two charged balls made of pith (a very light, spongy ma

Question

Hanging from threads are two charged balls made of pith (a very light, spongy material that comes from inside the stems of certain plants). The balls each have a mass of 0.100 g and a charge of the same magnitude q and are attracted toward each other, as shown in the figure below. (Take = 18.7° and r = 2.21 cm.) (a) What is the magnitude of the electric force? (b) What is the magnitude of q? (c) How many electrons have been transferred to or from each ball?

Explanation / Answer

Given that angle ? = 18° r = 2.21 cm. m = 0.100 g = 0.100x10^-3 kg Let the electrostatic force between the two charges is F Assume that the tension in the string is T The free body diagram for each mass as shown below. Apply Newton's law in vertical direction T cos? = mg Apply Newton's law in horizontal direction T sin? = F From the above two equations we get tan? = F / mg F = (mg)tan? kq*q / r^2 = (mg)tan? q^2 = mg tan? * r^2 / k = 0.1 x 10-3 * 9.8 *tan18 * (2.21 x 10-2)^2 / 9 x 10^9 = 0.1728 x 10-13 ==> q = 0.1314 x 10^-6 C The force between the two charges is F = kq*q / r^2 = 9 x 10^9 * (0.1314 x 10-6)^2 / (2.21 x 10-2)^2 = 0.3181 N The number of electrons related to the charge as q = ne n = q / e = 0.1314 x 10-6 / 1.6 x 10-19 = 8.2125 x 10^11 electrons

Related Questions

Navigate

• Browse (All)
• Browse H
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.