Pressure in Fluids Exe-4B Long Answer Physics Class-9 ICSE Selina Publishers

Pressure in Fluids and Atmospheric Pressure Exe-4B Atmospheric Pressure and it’s Measurement Long Answer Type for Class-9 ICSE Concise Physics. There is the solutions of Long Answer type Questions of your latest textbook which is applicable in 2023-24 academic sessionVisit official Website CISCE for detail information about ICSE Board Class-9.

Pressure in Fluids Exe-4B Atmospheric Pressure and it’s Measurement Long Answer 

(ICSE Class – 9 Physics Concise Selina Publishers)

Board ICSE
Class 9th
Subject Physics
Writer / Publication Concise selina Publishers
Chapter-4 Pressure in Fluids and Atmospheric Pressure
Exe – 4B Atmospheric Pressure and it’s Measurement
Topics Solution of Exe-4(B) Long Answer Type
Academic Session 2023-2024

Exe-4B Atmospheric Pressure and it’s Measurement Long Answer Type

Ch-4 Pressure in Fluids and Atmospheric Pressure Physics Class-9 ICSE Concise

Page 113

Question 1. What is a barometer? How is a simple barometer constructed ?


A barometer is an instrument which is used to measure the atmospheric pressure.

Construction of a simple barometer:

A simple mercury barometer can be made with a clear, dry, thick-walled glass tube about 1 metre ling. The glass tube is sealed at one end and is filled with mercury completely. While filling the tube with mercury care has to be taken so that there are no air bubbles present in the mercury column. Close the open end with thumb and turn the tube upside down carefully over a trough containing mercury. Dip the open end under the mercury level in the trough and remove the thumb.

working of simple barometer:

The mercury level in the tube falls until it is about 76 cm (h =760 mm) vertically above the mercury level. It is the atmospheric pressure acting on the surface of the mercury in the trough that supports the vertical mercury column. The empty space above the mercury column is called the ‘Torricellian vacuum’.


Question 2. Mention two demerits  of a simple barometer and state how they are removed in a Fortin barometer.


In a simple barometer, there is no protection for the glass tube but in Fortin’s barometer, this defect has been removed by enclosing the glass tube in a brass case.

In a simple barometer, a scale cannot be fixed with the tube (or it cannot be marked on the tube) to measure the atmospheric pressure but Fortin’s barometer is provided with a vernier calipers to measure the accurate reading.

Question 3. What is an altimeter? State its principle. How is its scale calibrated?


An altimeter is a device used in aircraft to measure its altitude.

Principle: Atmospheric pressure decreases with the increase in height above the sea level; therefore, a barometer measuring the atmospheric pressure can be used to determine the altitude of a place above the sea level.

The scale of altimeter is graduated with height increasing towards left because the atmospheric pressure decreases with increase of height above the sea level.

(Pressure in Fluids and Atmospheric Pressure Exe-4B Long Class-9 ICSE)

Question 4. Draw a simple labelled diagram of a Fortin barometer and state how it is used to measure the atmospheric pressure.


fortine barometer

To measure the atmospheric pressure, first the leather cup is raised up or lowered down with the help of the screw S so that the ivory pointer I just touches the mercury level in the glass vessel. The position of the mercury level in the barometer tube is noted with the help of main scale and the vernier scale. The sum of the vernier scale reading to the main scale reading gives the barometric height.

Question 5. What is an aneroid barometer? Draw a neat and labelled diagram to explain its construction and working.


A barometer calibrated to read directly the atmospheric pressure is called an aneroid barometer. It has no liquid, it is light and portable.

neroid barometer

Construction aneroid barometer

Figure above shows the main parts of an aneroid barometer. It consists of a metallic box B which is partially evacuated. The top D of the box is springy and corrugated in form of a diaphragm as shown. At the middle of diaphragm, there is a thin rod L toothed at its upper end. The teeth of rod fit well into the teeth of a wheel S attached with a pointer P which can slide over a circular scale. The circular scale is initially calibrated with a standard barometer so as to read the atmospheric pressure directly in terms of the barometric height.

Working aneroid barometer

 When atmospheric pressure increases, it presses the diaphragm D and the rod L gets depressed. The wheel S rotates clockwise and pointer P moves to the right on the circular scale. When atmospheric pressure decreases, the diaphragm D bulges out due to which the rod L moves up and the wheel S rotates anti-clockwise. Consequently, the pointer moves to the left.

—  : End of Pressure in Fluids and Atmospheric Pressure Exe-4B Long Answer Type  Solutions :–

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