In old age arteries carrying blood in the human body become narrow resulting in an increase in the blood pressure, this follows from

Options

A. 1. Pascal's law
B. 2. Stokes' law
C. 3. Bernoulli's principle
D. 4. Archimede's principle

Explanation

To solve the question regarding the increase in blood pressure due to the narrowing of arteries in old age, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Problem**:
- In old age, arteries become narrower, which affects blood flow and pressure.

2. **Applying the Equation of Continuity**:
- The equation of continuity states that the product of the cross-sectional area (A) and the velocity (V) of a fluid is constant along a streamline. Mathematically, this can be expressed as:
\[ A_1 V_1 = A_2 V_2 \]
- Here, \(A_1\) and \(V_1\) are the area and velocity in the wider section of the artery, and \(A_2\) and \(V_2\) are the area and velocity in the narrower section.

3. **Analyzing the Effect of Narrowing**:
- When the artery narrows, \(A_2 < A_1\). To maintain the continuity equation, the velocity must increase:
\[ V_2 > V_1 \]

4. **Applying Bernoulli's Theorem**:
- Bernoulli's theorem states that for an incompressible, non-viscous fluid flowing in a streamline, the following relationship holds:
\[ P + \frac{1}{2} \rho V^2 + \rho gh = \text{constant} \]
- Assuming the height (h) remains constant, we can simplify this to:
\[ P + \frac{1}{2} \rho V^2 = \text{constant} \]

5. **Relating Velocity and Pressure**:
- From Bernoulli's theorem, if the velocity \(V\) increases (as it does when the artery narrows), the pressure \(P\) must decrease to keep the equation balanced. Conversely, if the velocity decreases, the pressure increases.

6. **Conclusion**:
- In the case of narrowing arteries, as the blood flows from a narrower section to a wider section, the velocity decreases, resulting in an increase in pressure. Thus, the increase in blood pressure due to narrowing arteries follows Bernoulli's principle.

### Final Answer:
The increase in blood pressure due to the narrowing of arteries in old age follows **Bernoulli's theorem**.

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