Choose the incorrect statement.

Options

A. Dielectric constant of a material is a measure of degree of polarization when placed in external field
B. Dielectric constant of polar substances is more than non-polar substances
C. Metals have very low value of dielectric constant
D. Capacitance of a capacitor increases upon insertion of dielectric slab

Explanation

To solve the question, we need to analyze each statement provided in the options and determine which one is incorrect.

### Step-by-Step Solution:

1. **Understanding Dielectric Constant**:
- The dielectric constant (k) of a material is defined as the ratio of the electric field in a vacuum (E₀) to the electric field in the material (E). It is a measure of how much the material can polarize in response to an electric field, which reduces the overall electric field within the material.

2. **Analyzing Option 1**:
- The first statement claims that the dielectric constant of a material is a measure of the degree of polarization when placed in an electric field.
- This statement is **correct** because the dielectric constant indeed reflects how much a material can polarize under an electric field.

3. **Analyzing Option 2**:
- The second statement states that the dielectric constant of a polar substance is more than that of a non-polar substance.
- This statement is also **correct**. Polar substances have permanent dipoles that align with the electric field, resulting in a higher dielectric constant compared to non-polar substances.

4. **Analyzing Option 3**:
- The third statement asserts that metals have a very low value of dielectric constant.
- This statement is **incorrect**. Metals are considered to have a very high dielectric constant (theoretically infinite) because they can conduct electricity and effectively shield the electric field within them. Thus, the dielectric constant for metals is not low; it is very high.

5. **Analyzing Option 4**:
- The fourth statement mentions that the capacitance of a capacitor increases upon the insertion of a dielectric.
- This statement is **correct**. When a dielectric is inserted between the plates of a capacitor, it increases the capacitance due to the reduction in the electric field.

### Conclusion:
The incorrect statement among the options is the third one, which claims that metals have a very low value of dielectric constant.

### Final Answer:
**The incorrect statement is: "Metals have a very low value of dielectric constant."**

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