To solve the assertion and reason question regarding electrostatics, we will analyze both statements step by step.
### Step 1: Understanding the Assertion
The assertion states that "the field in a cavity inside a conductor is zero which causes electrostatic shielding."
- **Explanation**: According to electrostatic principles, when a conductor is in electrostatic equilibrium, the electric field inside the conductor is zero. If there is a cavity within the conductor, the electric field inside that cavity is also zero. This phenomenon is known as electrostatic shielding, where external electric fields do not penetrate the conductor and thus do not affect the cavity inside.
### Step 2: Applying Gauss's Law
To understand why the electric field is zero in the cavity, we can apply Gauss's Law.
- **Gauss's Law** states that the electric flux through a closed surface is proportional to the charge enclosed by that surface. Mathematically, it is given by:
\[
\Phi_E = \oint E \cdot dA = \frac{Q_{\text{enc}}}{\epsilon_0}
\]
- In the case of the cavity, if we consider a Gaussian surface just inside the conductor surrounding the cavity, the charge enclosed \( Q_{\text{enc}} \) is zero because there are no charges present in the cavity. Therefore, the electric flux \( \Phi_E \) is zero.
### Step 3: Conclusion from Gauss's Law
Since the electric flux is zero, it implies that the electric field \( E \) must also be zero in the cavity.
- **Mathematical Representation**:
\[
E \cdot A = 0 \Rightarrow E = 0 \text{ (since A is not zero)}
\]
- Thus, we confirm that the assertion is true.
### Step 4: Understanding the Reason
The reason states that "the dielectric constant of conductors in electrostatics is infinite."
- **Explanation**: The dielectric constant (or relative permittivity) of a material is a measure of its ability to reduce the electric field within it. For conductors, when they are in electrostatic equilibrium, they can completely shield the electric field, which leads to the concept that their dielectric constant can be considered infinite.
### Step 5: Validating the Reason
While the reason is true, it does not directly explain the assertion.
- The assertion is about the electric field being zero in the cavity, while the reason discusses the dielectric constant. Although both statements are true, the reason does not provide a direct explanation for why the electric field is zero in the cavity.
### Final Conclusion
Both the assertion and reason are true, but the reason does not explain the assertion. Therefore, the correct answer is:
**Answer**: Both assertion and reason are true, but the reason is not a correct explanation for the assertion.
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