Question

If more air is pushed in a soap bubble, the pressure in it
(A) decreases
(B) becomes zero
(C) remains same
(D) increases

Answer 1

Hint: we can use the information that if the size of the control volume increases, the pressure experienced by the particles present in the control volume becomes less. Also, we can use the expression of the excess pressure of the bubble for the determination of the correct answer.

Complete step by step solution:
As we know, the ideal gas equation gives information about pressure and volume. So, with the help of the ideal gas equation, we can say that the pressure relates inversely with the volume, it means that if we increase the control volume upto a certain amount, then the pressure in the control volume will decrease.
The soap bubble acts as control volume, and the particles present in the soap bubble feel some amount of pressure. If more air is pushed in a soap bubble, then the soap bubble expansion takes place, and its volume increases. Due to this expansion, the radius of the soap bubble increases. Using the relation of pressure and volume, we can say that pressure inside the bubble will decrease if volume increases. Also, from the expression of the bubble's excess pressure, we can determine whether pressure increases, decreases, or remains the same inside the bubble. In the expression, the excess pressure relates inversely with the radius of the bubble. So the radius of the bubble increases during expansion, so the large value of radius will give less pressure.
Therefore, if more air is pushed in a soap bubble, the pressure in the soap bubble decreases

So, the correct answer is “Option A”.

Note:
Remember that we can obtain the excess pressure of the soap bubble by taking the ratio of the four times of surface tension and bubble radius. In the ratio, the value of the soap radius comes in denominator and the value of surface tension comes in the numerator.