Metal sphere 1 has a positive charge of 7.00 nc . metal sphere 2, which is twice the diameter of sphere 1, is initially uncharged. the spheres are then connected together by a long, thin metal wire. what are the final charges on each sphere?

Respuesta :

Answer:

2.33 nC, 4.67 nC

Explanation:

when the two spheres are connected through the wire, the total charge (Q=7.00 nC) re-distribute to the two sphere in such a way that the two spheres are at same potential:

[tex]V_1 = V_2[/tex] (1)

Keeping in mind the relationship between charge, voltage and capacitance:

[tex]C=\frac{Q}{V}[/tex]

we can re-write (1) as

[tex]\frac{Q_1}{C_1}=\frac{Q_2}{C_2}[/tex] (2)

where:

Q1, Q2 are the charges on the two spheres

C1, C2 are the capacitances of the two spheres

The capacitance of a sphere is given by

[tex]C=4 \pi \epsilon_0 R[/tex]

where R is the radius of the sphere. Substituting this into (2), we find

[tex]\frac{Q_1}{4 \pi \epsilon_0 R_1}=\frac{Q_2}{4 \pi \epsilon_0 R_2}[/tex] (3)

we also know that sphere 2 has twice the diameter of sphere 1, so the radius of sphere 2 is twice the radius of sphere 1:

[tex]R_2 = 2R_1[/tex]

So the eq.(3) becomes

[tex]\frac{Q_1}{4 \pi \epsilon_0 R_1}=\frac{Q_2}{4 \pi \epsilon_0 2R_1}[/tex]

And re-arranging it we find:

[tex]Q_2 = 2Q_1[/tex]

And since we know that the total charge is

[tex]Q_1 + Q_2 = 7.00 nC[/tex]

we find

[tex]Q_1 = 2.33 nC\\Q_2 = 4.67 nC[/tex]

The final charges on the first and second spheres are 2.33 nC and 4.67 nC respectively.

Capacitance of a capacitor

The capacitance of a capacitor at a constant voltage is given by the following formula;

[tex]V = \frac{Q}{C} \\\\\frac{Q_1}{C_1} = \frac{Q_2}{C_2} \\\\[/tex]

For a metal sphere, C = 4πεR

[tex]\frac{Q_1}{4\pi \varepsilon _0 R_1} = \frac{Q_2}{4\pi \varepsilon _0 R_2}[/tex]

The diameter of the second sphere = 2 times the first sphere

R₂ = 2R₁

[tex]\frac{Q_1}{4\pi \varepsilon R_1} = \frac{Q_2}{4\pi \varepsilon 2R_1}\\\\Q_2 = 2Q_1[/tex]

Sum of the charges

Q₁ + Q₂ = 7

Q₁ + 2Q₁ = 7

3Q₁ = 7

Q₁ = 7/3

Q₁ = 2.33 nC

Q₂ = 2Q₁ = 2(2.33) = 4.67 nC

Thus, the final charges on the first and second spheres are 2.33 nC and 4.67 nC respectively.

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