Paper II · Part B — Physics

Pressure and Barometer

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Build exam-ready understanding by connecting the core idea, formulas or facts, worked example and previous NDA questions. Focus on why each rule works, then test it under timed conditions.

Concept

Pressure is force per unit area. Fluids exert pressure that increases with depth; atmospheric pressure is measured with a barometer.

The mercury barometer was devised by Torricelli.

Key Points & Formulas

Pressure = force / area (pascal).
Liquid pressure = hρg (depth × density × g); independent of area.
Atmospheric pressure ≈ 76 cm of mercury at sea level.
A barometer measures atmospheric pressure; a manometer measures gas pressure.

Worked Example

Q. Why does a sharp knife cut better than a blunt one?

A sharp edge has a very small contact area.

For the same force, pressure = force/area is much larger.

Higher pressure cuts more easily.

Common traps

Reading the prompt too quickly and missing a qualifier.
Memorising the result without checking when it applies.
Skipping units, signs, chronology or the final reasonableness check.

NDA shortcuts

State the governing rule before substituting values.
Eliminate impossible options before doing full calculation.

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5 NDA questions

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Question 1

NDA II 2023

A block of wood (dimensions: 40 cm × 20 cm × 10 cm) is kept on a tabletop in three different positions: (a) with its side of dimensions 20 cm × 10 cm; (b) with its side of dimensions 10 cm × 40 cm; and (c) with its side of dimensions 40 cm × 20 cm. The pressure exerted by the wooden block on the tabletop in these positions is represented by $P_A$ , $P_B$ and $P_C$ , respectively. The pressure follows the trend

Question 2

NDA II 2022

A pressure cooker cooks food faster by

Question 3

NDA I 2018

Which one of the following devices is used to measure atmospheric pressure?

Question 4

NDA II 2017

Water boils at a lower temperature at high altitudes, because

Question 5

NDA II 2016

Pressure is a scalar quantity because

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