Exams › NEET › Physics

A solid metallic sphere has charge $+3Q$. Concentric with this sphere is a conducting spherical shell having charge $-Q$. The radius of the sphere is $a$ and that of the spherical shell is $b$ $(b>a)$. What is the electric field at a distance $R$ such that $a<R<b$ from the centre?

1. $\dfrac{Q}{2\pi\varepsilon_0 R^2}$
2. $\dfrac{3Q}{2\pi\varepsilon_0 R^2}$
3. $\dfrac{3Q}{4\pi\varepsilon_0 R^2}$
4. $\dfrac{4Q}{4\pi\varepsilon_0 R^2}$

Correct answer: $\dfrac{3Q}{4\pi\varepsilon_0 R^2}$

Solution

For $a<R<b$, a Gaussian surface encloses only the charge on the inner metallic sphere, which is $+3Q$. The charge on the outer shell does not affect the field inside its material region. Using Gauss’s law gives $E\cdot 4\pi R^2=3Q/\varepsilon_0$.

Related NEET Physics questions

• Which of the following statements is not true about Gauss's law?
• A positive charge and a negative charge are held in place and initially form a dipole. Then a uncharged conducting bar is placed in between them. How is the force between the charges affected?
• The capacitance of a parallel-plate capacitor is 10 μF without the dielectric. A material with dielectric constant 2 is used to fill half the thickness between the plates. The new capacitance is:
• A point charge is brought in an electric field. The electric field at a nearby point: This question has multiple correct options
• Assertion A capacitor can be given only a limited quantity of charge Reason A capacitor is an arrangement which can store sufficient quantity of charge
• A soap bubble of radius 3 cm is charged with surface charge density σ such that (σ²)/(ε₀)=0.4 S I units. The excess pressure inside the bubble in SI unit (surface tension of soap solution =3 × 10⁻³ N / m) is:

⚔️ Practice NEET Physics free + battle 1v1 →