The minimum force required to separate a light glass plate of perimeter 5m from a water surface is (Given surface tension of water = `70 xx 10^(-3)`N/m)

Options

A. `350 xx 10^(-3)`N
B. `75 xx 10^(-3)`N
C. `100 xx 10^(-3)`N
D. `150 xx 10^(-3)` N

Answer

To solve the problem of finding the minimum force required to separate a light glass plate from a water surface, we can follow these steps:

### Step 1: Understand the Concept of Surface Tension
Surface tension is the force per unit length acting at the surface of a liquid. It is responsible for the cohesive forces between liquid molecules, which creates a "film" at the surface.

### Step 2: Identify the Given Values
- Perimeter (L) of the glass plate = 5 m
- Surface tension (S) of water = \(70 \times 10^{-3} \, \text{N/m}\)

### Step 3: Use the Formula for Force
The minimum force (F) required to separate the glass plate from the water surface can be calculated using the formula:
\[ F = S \times L \]
where:
- \(F\) is the force,
- \(S\) is the surface tension,
- \(L\) is the perimeter of the glass plate.

### Step 4: Substitute the Given Values into the Formula
Now, substituting the values into the formula:
\[ F = (70 \times 10^{-3} \, \text{N/m}) \times (5 \, \text{m}) \]

### Step 5: Perform the Calculation
Calculating the force:
\[ F = 70 \times 10^{-3} \times 5 = 350 \times 10^{-3} \, \text{N} \]

### Step 6: Final Result
Thus, the minimum force required to separate the light glass plate from the water surface is:
\[ F = 350 \times 10^{-3} \, \text{N} \quad \text{or} \quad 0.350 \, \text{N} \]

### Conclusion
The correct answer is \(350 \times 10^{-3} \, \text{N}\).

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