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There are two identical, positively charged conducting spheres fixed in space. The spheres are 40.4 cm apart (center to center) and repel each other with an electrostatic force of F1=0.0720 N . A thin conducting wire connects the spheres, redistributing the charge on each sphere. When the wire is removed, the spheres still repel, but with a force of F2=0.115 N . The Coulomb force constant is k=1/(4π????0)=8.99×109 N⋅m2/C2 . Using this information, find the initial charge on each sphere, q1 and q2 , if q1 is initially less than q2 .

1 Answer

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Answer:


q_1=5.64* 10^(-7)\ \text{C} and
q_2=2.32* 10^(-6)\ \text{C}

Step-by-step explanation:


F_1=0.072\ \text{N}


F_2=0.115\ \text{N}

r = Distance between shells = 40.4 cm


q_1 and
q_2 are the charges


k = Coulomb constant =
8.99*10^(9)\ \text{Nm}^2/\text{C}^2

Force is given by


F_1=(kq_1q_2)/(r^2)\\\Rightarrow q_1q_2=(F_1r^2)/(k)\\\Rightarrow q_1q_2=(0.072* 0.404^2)/(8.99* 10^(9))\\\Rightarrow q_1q_2=1.307* 10^(-12)\\\Rightarrow q_1=(1.307* 10^(-12))/(q_2)


F_2=(kq^2)/(r^2)\\\Rightarrow q=\sqrt{(F_2r^2)/(k)}\\\Rightarrow q=\sqrt{(0.115* 0.404^2)/(8.99* 10^(9))}\\\Rightarrow q=1.44* 10^(-6)\ \text{C}


q=(q_1+q_2)/(2)\\\Rightarrow q_1+q_2=2q\\\Rightarrow q_1+q_2=2*1.44* 10^(-6)\\\Rightarrow q_1+q_2=2.88* 10^(-6)

Substituting the above value of
q_1 we get


(1.307* 10^(-12))/(q_2)+q_2=2.88* 10^(-6)\\\Rightarrow q_2^2-2.88* 10^(-6)q_2+1.307* 10^(-12)=0\\\Rightarrow \frac{-\left(-0.00000288\right)\pm \sqrt{\left(-0.00000288\right)^2-4* \:1* \:1.307* 10^(-12)}}{2* \:1}\\\Rightarrow q_2=2.32* 10^(-6), 5.64* 10^(-7)


q_1=(1.307* 10^(-12))/(q_2)=(1.307* 10^(-12))/(2.32* 10^(-6))\\\Rightarrow q_1=5.63* 10^(-7)


q_1=(1.307* 10^(-12))/(q_2)=(1.307* 10^(-12))/(5.64* 10^(-7))\\\Rightarrow q_1=2.32* 10^(-6)

Since we know
q_1<q_2


q_1=5.64* 10^(-7)\ \text{C} and
q_2=2.32* 10^(-6)\ \text{C}.

User Brijesh Bhatt
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