A conducting sphere of radius 10 cm is charged with 10 μC. Another ...
Given data:
- Radius of first sphere (charged sphere), \(r_1 = 10 \, \text{cm}\)
- Charge on first sphere, \(Q_1 = 10 \, \mu C\)
- Radius of second sphere (uncharged sphere), \(r_2 = 20 \, \text{cm}\)
Step 1: Determine the charge on the uncharged sphere after touching
- When the uncharged sphere touches the charged sphere, charge will transfer from the charged sphere to the uncharged sphere until they reach the same potential.
- Using conservation of charge, the final total charge is equal to the initial total charge.
- Let \(Q_2\) be the final charge on the uncharged sphere.
- Therefore, \(Q_1 + Q_2 = Q_1' + Q_2'\)
- \(Q_2 = Q_1' + Q_2' - Q_1 = Q_2'\)
- The final charges on both spheres will be equal.
Step 2: Calculate the surface charge density ratio
- Surface charge density, \(\sigma = \frac{Q}{4\pi r^2}\)
- For the first sphere, \(\sigma_1 = \frac{Q_1'}{4\pi r_1^2}\)
- For the second sphere, \(\sigma_2 = \frac{Q_2'}{4\pi r_2^2}\)
- From step 1, \(Q_1' = Q_2'\)
- Therefore, \(\frac{\sigma_1}{\sigma_2} = \frac{Q_1'}{4\pi r_1^2} \times \frac{4\pi r_2^2}{Q_2'} = \frac{Q_1'}{Q_2'} = 1\)
- Hence, the surface density of charges on the spheres will be in the ratio of 1:1, which is equivalent to 2:2 or 2:1. Thus, option 'D' is correct.