91Ó°ÊÓ

The given data is listed below as:

• The radius of the hollow ball is,$r=7\text{cm}×\left(\frac{\text{1}\text{m}}{\text{100}\text{cm}}\right)=0.07\text{m}$
• The charge of the hollow ball is,$Q=-9×{10}^{-8}\text{C}$
• The distance of the location A from the surface of the sphere is,$l=1\text{cm}×\left(\frac{\text{1}\text{m}}{\text{100}\text{cm}}\right)=\text{0.01}\text{m}$
• The distance of the location B from the surface of the sphere is,$s=2\text{cm}×\left(\frac{\text{1}\text{m}}{\text{100}\text{cm}}\right)=\text{0.02}\text{m}$

The electric field is described as a region that helps an electrically charged particle to exert force on another particle. The magnitude of the electric field is directly proportional to the charge of that object and inversely proportional to the distance between the center of the electric field and the charge.

The first statement (a) states that at location A, is . This statement is incorrect as in the center of an insulator, the electric field is zero and the location A is not at the center even though the charge on the sphere’s outside is distributed uniformly.

The second statement (b) states that All of the charges on the surface of the sphere contribute to at location A. This statement is correct as this is the main reason the electrical field of is not zero.

Thus, the statement (a) is incorrect.

The statement (b) is correct.

The equation of the magnitude of the electric field of the hollow ball at the location B is expressed as:

$E_{\text{ball}}=k\frac{Q}{{\left(r+s\right)}^2}$

Here, is the electric field constant, is the charge of the hollow ball, is the radius of the hollow ball and is the distance of the location B from the surface of the sphere.

Substitute the values in the above equation.

$$\begin{gathered} E_{\text{ball}}=\left(9×{10}^9\text{N}·{\text{m}}^{\text{2}}{\text{/C}}^{\text{2}}\right)\frac{-9×{10}^{-8}\text{C}}{{\left(0.07\text{m}+0.02\text{m}\right)}^2} \\ =\frac{-810\text{N}·{\text{m}}^{\text{2}}\text{/C}}{{\left(0.09\text{m}\right)}^2} \\ =\frac{-810\text{N}·{\text{m}}^{\text{2}}\text{/C}}{\left(8.1×{10}^{-3}{\text{m}}^2\right)} \\ =-1×{10}^5\text{N/C} \end{gathered}$$

Thus, at location B is$-1×{10}^5\text{N/C}$ .