Question

How does the atmospheric pressure change with altitude?
(A). Altitude increases, pressure decreases
(B). Altitude decreases, pressure increases
(C). Altitude increases, pressure increases
(D). Altitude is independent of pressure

Answer 1

The pressure is the force acting on the unit area. Pressure of fluids also depends on the density, height and acceleration due to gravity. As we go to higher altitudes, we experience phenomena like altitude sickness due to change in external pressure.

Formula used:
$P=\dfrac{force}{area}$

Complete step-by-step solution:
Pressure is defined as the force acting on a unit area. Its Si unit is pascal (P).
It is given as-
$P=\dfrac{force}{area}$
All fluids exert a pressure on their surroundings. Water kept in a container exerts pressure equally in all the directions as well as on the walls of the container. Similarly, the blanket of air around us exerts a pressure on our bodies.
For, pressure in fluids,
$P=\rho gh$
Here,
$P$ is the pressure
$\rho$ is the density
$h$ is the height
$g$ is acceleration due to gravity
From the above equation, for a particular medium,
$P\propto h$
But as we go to higher altitudes, the atmosphere becomes thinner as our distance from the blanket of atmosphere decreases and hence, $h$decreases, so the pressure also decreases. There is less oxygen at higher altitudes because of which we experience altitude sickness. The blood pressure becomes greater than the external pressure acting on our bodies due to which our ears tend to pop.
Pressure is directly proportional to height. Therefore as altitude increases pressure decreases.

Hence, the correct options are (A) and (B).

Note:
As we go to places of higher altitudes, the air gets thinner due to which the pressure also decreases. As we go deeper into the ocean, the amount of water exerting pressure on our bodies increases and hence pressure increases. At the same height, a denser fluid exerts more pressure than a rarer fluid.