Unit II Physics NDA : Some Important Facts about Physical properties

Some Important Facts

Normal atmospheric pressure is equal to 76 cm of height of mercury in the Barometer.

If h is the barometric height for a liquid of density d, then,

hdg = 76 x 13.6 x g or h = 76 x 13.6 / d

Relative Density = Density of Body / Density of Water at 4°C

A pressure applied at any point of the fluid is equally transmitted in all the directions.

Pressure is force acting perpendicular on unit area of a surface.

Pressure (P) = Force (F) / Area (A)

Pressure is scalar quantity and its unit is N/m² or Pascal (Pa).

Density of a substance can be defined as the ratio of its mass to its volume.

Density (d) = Mass (M) / Volume (v)

The unit of density is kg / m³

If we mix equal volumes of two liquids of density d₁ and d₂, then the density of the mixture is

d = d₁ + d₂ / 2

If we mix two liquids of same mass with densities d₁ and d₂, then the density of the mixture is

d = 2d₁d₂ / d₁ + d₂

If we mix two liquids of mass m₁ and m₂ having densities d₁ and d₂, then the density of the mixture is

d = m₁ + m₂ / m₁/d₁ + m₂/d₂

UNIT 1 : Physical Properties and States

UNIT I

Physical Properties and States of Matter, Mass, Weight, Volume, Density and Specific Gravity, Principle of Archimedes, Pressure Barometer.

Archimedes principle states that the buoyant force on an object is going to be equal to the weight of the fluid displaced by the object, or the density of the fluid multiplied by the submerged volume. In simpler terms, the weight of the displaced fluid is directly proportional to the volume of the displaced fluid (if the surrounding fluid is of uniform density).

This principle states that when a body (totally or partially) is immersed in a fluid, it appears to lose a part of its weight and the apparent loss of weight is equal to the weight of fluid displaced.

Apparent weight of body = Actual Weight of Body - Upthrust

= [mg - m / d x ρg]

= mg [1 - ρ / d]

where, d = density of body and

ρ = density of fluid.

It may be noted that buoyant force depends on the density of the fluid and not on the density of body acting on centre of gravity of fluid.

Archimedes Law of Floatation

The principle of floatation states that when a floating body like wood is placed in water, it sinks until the weight of water displaced by it is just equal to its own weight and then it floats. There are various situations that are to be understood.

When a body is immersed in a fluid then if

The weight W of body is more than the up - thrust W' (W > W'), the body will sink.

The weight W of the body is equal to up - thrust W' (W' = W), the body floats with whole of its volume inside the liquid.

The weight (W < W'), the body will float with some of its part outside the liquid.

When a block of ice floats in a liquid whose density is greater than that of water, the level of liquid will rise when all the ice melts into water. On the other hand, when an ice block floats in a liquid that have density less than that of water, the level of liquid will fall when all the ice melts into water. It may be noted that when an ice block floats in water, the water level will remain the same when all the ice melts into water.

NDA PHYSICS SYLLABUS

PHYSICS SYLLABUS FOR NDA EXAMS

Physical Properties and States of Matter, Mass, Weight, Volume, Density and Specific Gravity, Principle of Archimedes, Pressure Barometer.

Motion of objects, Velocity and Acceleration, Newton’s Laws of Motion, Force and Momentum, Parallelogram of Forces, Stability and Equilibrium of bodies, Gravitation, elementary ideas of work, Power and Energy.

Effects of Heat, Measurement of temperature and heat, change of State and Latent Heat, Modes of transference of Heat.

Sound waves and their properties, Simple musical instruments.

Rectilinear propagation of Light, Reflection and refraction. Spherical mirrors and Lenses. Human Eye.

Natural and Artificial Magnets, Properties of a Magnet, Earth as a Magnet.

Static and Current Electricity, conductors and Non-conductors, Ohm’s Law, Simple Electrical Circuits, Heating, Lighting and Magnetic effects of Current, Measurement of Electrical Power, Primary and Secondary Cells, Use of X-Rays.

General Principles in the working of the following :

Simple Pendulum, Simple Pulleys, Siphon, Levers, Balloon, Pumps, Hydrometer, Pressure Cooker, Thermos Flask, Gramophone, Telegraphs, Telephone, Periscope, Telescope, Microscope, Mariner’s Compass; Lightening Conductors, Safety Fuses.

 Physics :

 Physical Properties and States of Matter, Mass, Weight, Volume, Density and Specific Gravity, Principle of Archimedes, Pressure Barometer. Motion of objects, Velocity and Acceleration, Newtons Laws of Motion, Force and Momentum, Parallelogram of Forces, Stability and Equilibrium of bodies, Gravitation, elementary ideas of work, Power and Energy. Effects of Heat, Measurement of temperature and heat, change of State and Latent Heat, Modes of transference of Heat. Sound waves and their properties, Simple musical instruments. Rectilinear propagation of Light, Reflection and refraction. Spherical mirrors and Lenses. Human Eye. Natural and Artificial Magnets, Properties of a Magnet, Earth as a Magnet. Static and Current Electricity, conductors and Non-conductors, Ohm’s Law, Simple Electrical Circuits, Heating, Lighting and Magnetic effects of Current, Measurement of Electrical Power, Primary and Secondary Cells, Use of X-Rays.

General Principles in the working of the following :

Simple Pendulum, Simple Pulleys, Siphon, Levers, Balloon, Pumps, Hydrometer, Pressure Cooker, Thermos Flask, Gramophone, Telegraphs, Telephone, Periscope, Telescope, Microscope, Mariner’s Compass; Lightening Conductors, Safety Fuses.