Laxmi

Temperature and its Measurement:
Temperature of a body is the degree of hotness or coldness of the body. Highest possible temperature achieved in laboratory is about 10⁸K, while lowest possible temperature attained is 10^-8 K. Temperature is measured with a thermometer.

We are giving a detailed and clear sheet on all Physics Notes that are very useful to understand the Basic Physics Concepts.

Temperature and its Measurement in Physics – Thermometry and Calorimetry

Branch of Physics dealing with production and measurement of temperature close to 0 K is known as cryagenics, while that dealing with the measurement of very high temperature is called pyrometry.

Temperature of the core of the sun is 10⁷ K while that of its surface is 6000 K.

NTP or STP implies 273.15 K (0°C = 32°F).

Different Scales of Temperature and Their Relationship
(i) Celsius Scale:
In this scale of temperature, the melting point of ice is taken as 0°C and the boiling point of water as 100°C and the space between these two points is divided into 100 equal parts.

(ii) Fahrenheit Scale:
In this scale of temperature, the melting point of ice is taken as 32°F and the boiling point of water as 212°F and the space between these two points is divided into 180 equal parts.

(iii) Kelvin Scale:
In this scale of temperature, the melting point of ice is taken as 273 K and the boiling point of water as 373 K and the space between these two points is divided into 100 equal parts.

(iv) Reaumer Scale:
In this scale of temperature, the melting point of ice is taken as 0°R and the boiling point of water as 80°R and the space between these two points is divided into 80 equal parts.

The Relation Between Different Scales of Temperatures

\(\frac{C}{100}=\frac{F-32}{180}=\frac{K-273}{100}=\frac{R}{80}\)

Absolute Temperature Means:
There is no limit for maximum temperature but there is a sharp point for minimum temperature that nobody can have the temperature lower than this minimum value of temperature, which is known as absolute temperature.

Thermometry and Calorimetry:
The thermometer is a device used to check the temperature of an object. This branch of measurement of the temperature of a substance is called thermometry. It is measured in degrees or Fahrenheit, usually.

Calorimetry also means the measurement of heat but in joules. It states the amount of heat lost by the body is the amount of heat gained by its surrounding.

Heat Energy	Temperature and its Measurement
Thermometric Property	Thermometers
Thermal Expansion	Thermal Equilibrium
Triple Point of Water	Specific Heat Capacity
Thermal Capacity	Water Equivalent
Latent Heat	Joule’s Law
Calorimetry

Heat Definition Physics:
The definition of heat is a form of energy that causes a difference in temperature, or the perception of warmth. An example of heat is hot water.

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What is Heat in Physics? | Definition, Formula, Types, Units – Thermometry and Calorimetry

Heat is a form of energy called thermal energy which flows from a (hotter) higher temperature body to a lower temperature body (colder) when they are placed in contact.

Heat or thermal energy of a body is the sum of kinetic energies of all its constituent particles, on account of translational, vibrational and rotational motion.

Types of Heat Transfer:
Heat is transfered via

• Solid material (conduction)
• Liquids and gases (convection) and
• Electromagnetic waves (radiation).

Heat Formula in Thermodynamics:
The equation for calculating heat energy is

Q = mC_pΔT

Where,
Q is the heat variable, (cal or J)
m is the mass of the object,
C_p is the specific heat constant and (J/g)
ΔT is the temperature change.

Heat Units Physics:
The SI unit of heat energy is joule (J).
The practical unit of heat energy is calorie.

1 cal = 4.18 J

1 calorie is the quantity of heat required to raise the temperature of 1 g of water by 1°C (from 14.5°C to 15.5°C).

Mechanical energy or work (W) can be converted into heat (Q) by

W = JQ

where,
J = Joule’s mechanical equivalent of heat.
J is a conversion factor (not a physical quantity) and its value is 4.186 J/cal.

Thermometry and Calorimetry:
The thermometer is a device used to check the temperature of an object. This branch of measurement of the temperature of a substance is called thermometry. It is measured in degrees or Fahrenheit, usually.

Calorimetry also means the measurement of heat but in joules. It states the amount of heat lost by the body is the amount of heat gained by its surrounding.

Heat Energy	Temperature and its Measurement
Thermometric Property	Thermometers
Thermal Expansion	Thermal Equilibrium
Triple Point of Water	Specific Heat Capacity
Thermal Capacity	Water Equivalent
Latent Heat	Joule’s Law
Calorimetry

Molecular Range Meaning:
The maximum distance upto which a molecule can exert a force of attraction on other molecules is called molecular range.

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Molecular Range | Meaning – Surface Tension

The molecular range is different for different substances.

• In solids and liquids, it is of the order of 10^-9m.
• If the distance between the molecules is greater than 10^-9 m, the force of attraction between them is negligible.

Molecular Range in Surface Tension:
Surface tension has been well- explained by the molecular theory of matter. According to this theory, cohesive forces among liquid molecules are responsible for the phenomenon of surface tension. The molecules well inside the liquid are attracted equally in all directions by the other molecules.

Surface Tension:
In Physics, the tension of the surface film of a liquid because of the attraction of the surface particles by the bulk of the liquid, which tries to minimize surface area is called surface tension. When the surface of the liquid is strong enough, then surface tension is applicable. It is strong enough to hold weight.

Surface Tension	Adhesive Force
Cohesive Force	Molecular Range
Factors Affecting Surface Tension	Surface Energy
Angle of Contact	Capillarity
Jurin’s Law

Factors Affecting Surface Tension in Physics – Surface Tension

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Factors Affecting Surface Tension

1. Surface tension of a liquid decreases with increase in temperature and becomes zero at critical temperature.
2. At boiling point, surface tension of a liquid becomes zero and becomes maximum at freezing point.
3. Surface tension decreases when partially soluble impurities such as soap, detergent, dettol, phenol etc are added in water.
4. Surface tension increases when highly soluble impurities such as salt is added in water.
5. When dust particles or oil spreads over the surface of water, its surface tension decreases.
6. When charge is given to a soap bubble, its size increases because surface tension of the liquid decreases due to electrification.
7. In weightlessness condition, liquid does not rise in a capillary tube.

Surface Tension:
In Physics, the tension of the surface film of a liquid because of the attraction of the surface particles by the bulk of the liquid, which tries to minimize surface area is called surface tension. When the surface of the liquid is strong enough, then surface tension is applicable. It is strong enough to hold weight.

Surface Tension	Adhesive Force
Cohesive Force	Molecular Range
Factors Affecting Surface Tension	Surface Energy
Angle of Contact	Capillarity
Jurin’s Law

Jurin’s Law | Definition, Formula – Surface Tension

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Jurin’s Law Definition:
If a capillary tube of insufficient length is placed vertically in a liquid, then liquid never come out from the tube on its own, as

Rh = constant ⇒ R₁h₁ = R₂h₂

where,
R = radius of curvature of liquid meniscus and
h = height of liquid column.
When a tube is kept in inclined position in a liquid and the vertical height h remains unchanged, then length of liquid column
Image

cos α = \(\frac{h}{l}\) or l = \(\frac{h}{cos α}\)

Liquid rises (water in glass capillary) or falls (mercury in glass capillary) due to property of surface tension

Jurin’s Law Formula:

S = \(\frac{R \rho g h}{2 \cos \theta}\)

where,
R = radius of capillary tube,
h = height of liquid,
ρ = density of liquid,
θ = angle of contact,
S = surface tension of liquid and
g = acceleration due to gravity.

Surface Tension:
In Physics, the tension of the surface film of a liquid because of the attraction of the surface particles by the bulk of the liquid, which tries to minimize surface area is called surface tension. When the surface of the liquid is strong enough, then surface tension is applicable. It is strong enough to hold weight.

Surface Tension	Adhesive Force
Cohesive Force	Molecular Range
Factors Affecting Surface Tension	Surface Energy
Angle of Contact	Capillarity
Jurin’s Law

Surface Tension:
Surface tension is the property of any liquid by virtue of which it tries to minimise its free surface area.

Surface tension of a liquid is measured as the force acting per unit length on an imaginary line drawn tangentially on the free surface of the liquid.

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What is Surface Tension in Physics | Definition, Formula, Units – Surface Tension

Surface Tension formula:

Surface tension, S= \(\frac{\text { Force }}{\text { Length }}=\frac{F}{l}=\frac{\text { Work done }}{\text { Change in area }}\)

Where,
S is the surface tension of the liquid
F is the force per unit length
L is the length in which force act

Surface Tension units:
SI unit is Nm^-1 or Jm^-2
CGS unit is dyn/cm

Surface Tension Dimensional Formula:
Dimensional formula is [MT^-2].

It is a scalar quantity. Surface tension is a molecular phenomenon which is due to cohesive force.

Surface tension of a liquid depends only on the nature of liquid and is independent of the surface area of film or length of the line considered.

Small liquid drops are spherical due to the property of surface tension.

Some Phenomena Based on Surface Tension

1. Medicines used for washing wounds, as dettol, have a surface tension lower than water.

2. Hot soup is more tasteful than the cold one because the surface tension of the hot soup is less than that of the cold and so it spreads over a larger area of the tongue.

3. Insects and mosquitoes swim on the surface of water in ponds and lakes due to surface tension. If kerosene oil is sprayed on the water surface, the surface tension of water is lowered and the insects and mosquitoes sink in water and are dead.

4. If we deform a liquid drop by pushing it slightly, then due to surface tension it again becomes spherical.

5. The detergents are used for cleaning the dirty clothes. The molecule of detergent can attached with water and dirt molecules and they take away the dirt with them, when we wash the clothes with detergent.

Surface Tension:
In Physics, the tension of the surface film of a liquid because of the attraction of the surface particles by the bulk of the liquid, which tries to minimize surface area is called surface tension. When the surface of the liquid is strong enough, then surface tension is applicable. It is strong enough to hold weight.

Surface Tension	Adhesive Force
Cohesive Force	Molecular Range
Factors Affecting Surface Tension	Surface Energy
Angle of Contact	Capillarity
Jurin’s Law

Poiseuille’s Law Definition:
The law of Poiseuille states that the flow of liquid depends on the following variables such as the length of the tube(L), radius (r), pressure gradient (∆P) and the viscosity of the fluid (η) in accordance with their relationship.

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Poiseuille’s Law | Definition, Formula – Hydrodynamics

Poiseuille’s Law Formula:
The rate of flow (u) of liquid through a horizontal pipe for steady flow is given by

v = \(\frac{\pi}{8} \frac{p r^{4}}{\eta l}\)

where,
p = pressure difference across the two ends of the tube,
r = radius of the tube,
η = coefficient of viscosity,
l = length of the tube.

Hydrodynamics:
In physics, hydrodynamics of fluid dynamics explains the mechanism of fluid such as flow of liquids and gases. It has a wide range of applications such as evaluating forces and momentum on aircraft, prediction of weather, etc.

Flow of liquid	Reynold’s Number
Equation of Continuity	Energy of a Liquid
Bernoulli’s Principle	Venturimeter
Torricelli’s Theorem	Viscosity
Poiseuille’s Law	Rate of Flow of Liquid
Stoke’s Law and Terminal Velocity	Critical Velocity

Rate of Flow of Liquid | Methods – Hydrodynamics

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Rate of Flow of Liquid:
Rate of Flow of Liquid through a capillary tube is given by

v = \(\frac{p}{R}\)

where,
R = \(\frac{8 \eta l}{\pi r^{4}}\) called liquid resistance and
p = liquid pressure.

(i) When two tubes are connected in series:

(a) Resultant pressure difference,

p = p₁ + p₂.

(b) Rate of flow of liquid (v) is same through both tubes.
(c) Equivalent liquid resistance,

R = R₁ + R₂.

(ii) When two tubes are connected in parallel:

(a) Pressure difference (p) is same across both tubes.
(b) Rate of flow of liquid v = v₁ + v₂.
(c) Equivalent liquid resistance = \(\frac{1}{R}=\frac{1}{R_{1}}+\frac{1}{R_{2}}\)

Hydrodynamics:
In physics, hydrodynamics of fluid dynamics explains the mechanism of fluid such as flow of liquids and gases. It has a wide range of applications such as evaluating forces and momentum on aircraft, prediction of weather, etc.

Flow of liquid	Reynold’s Number
Equation of Continuity	Energy of a Liquid
Bernoulli’s Principle	Venturimeter
Torricelli’s Theorem	Viscosity
Poiseuille’s Law	Rate of Flow of Liquid
Stoke’s Law and Terminal Velocity	Critical Velocity

What is Venturimeter? | Definition, Advantages, Disadvantages – Hydrodynamics

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Venturimeter Definition:
It is a device used for measuring the rate of flow of liquid through pipes. Its working is based on Bernoulli’s theorem.
Rate of flow of liquid,

v = a₁a₂\(\sqrt{\frac{2 g h}{a_{1}^{2}-a_{2}^{2}}}\)

where, a₁ and a₂ are area of cross-sections of tube at broader and narrower part and h is difference of liquid columns in vertical tubes.

Advantages:

• Low losses.
• Suitable for the large diameter of the pipe.
• It can be installed vertically, horizontally, inclined.
• Less chance of getting stuck with sediment.

Disadvantages:

• They are large in size and, therefore, where space is limited, they can not be used.
• Maintenance is not easy.
• Required more space.
• It is expensive in installation and replacement.
• It is not suitable for pipe diameter below then 75mm.

Hydrodynamics:
In physics, hydrodynamics of fluid dynamics explains the mechanism of fluid such as flow of liquids and gases. It has a wide range of applications such as evaluating forces and momentum on aircraft, prediction of weather, etc.

Flow of liquid	Reynold’s Number
Equation of Continuity	Energy of a Liquid
Bernoulli’s Principle	Venturimeter
Torricelli’s Theorem	Viscosity
Poiseuille’s Law	Rate of Flow of Liquid
Stoke’s Law and Terminal Velocity	Critical Velocity