Question bank for practice

 

Question Bank

 Very Short Answer  (1 Marks)   

                                                                                                                                       

1)     Which of the following pairs has the same dimensions?

          (a) specific heat and latent heat
          (b) lmpulse and momentum
          (c) surface tension and force
          (d) moment of lnertia and torque

2)     The atmospheric pressure is 106 dyne/cm². What is its value in SI unit?

          (a) 105 newton/m²
          (b) 106 newton/m²
          (c) 104 newton/m²
          (d) 103 newton/m²

3)     In SI system the fundamental units are

          (a) meter, kilogram, second, ampere, Kelvin, mole and candela
          (b) meter, kilogram, second, coulomb, Kelvin, mole and candela
          (c) meter, Newton, second, ampere, Kelvin, mole and candela
          (d) meter, kilogram, second, ampere, Kelvin, mole and lux

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Hooke's law

Hooke's  law

Introduction : Robert hooke , an english physicist studied the mechanical properties of solid and studied the tension in the solid and gave some law called as hooke's law. He studied elastic limit of a material and obtained very important result which gave a momentum to the world of mechanics. Let us discuss it in detail in this topic.

Elastic limit : The value of stress , upto which the stress is directly proportional to strain is called as Elastic limit.

Hooke's Law : Within elastic limit, stress is directly proportional to strain.

Mathematically,

Stress vs Strain graph

The constant is called as modulus of elasticityy

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Modulus of elasticity : It is defines as ratio of stress to strain.

Modulus of elasticity cam be classified into three category based on the types of stress and strain.

1) Young's Modulus (Y) : Young’s modulus is the ratio of longitudinal stress to longitudinal strain.

Consider a wire of length 'L' having radius 'r' and a mass 'm' is suspended below it. Due to this mass, a small extension 'l' is obtained in the wire and and 'L+l' is the final length of the wire. Thus the young's modulus for this system is given as,

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2) Bulk Modulus (K) : Bulk modulus is the ratio of volume stress to volume strain.

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3) Bulk Modulus (η) : modulus of rigidity is the ratio of shearing stress to shearing strain.

_{│<<<Strain│   │Stress and strain curve>>>│} 

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Strain

 Strain

Introduction : Strain plays an important factor in determining the mechanical properties of solids. We are going to see strain  in more details

Photo by billow926 on Unsplash

Strain : It is defines as ratio of change in dimension to original dimension.

Mathematically,

                           

There are three type of strain

1) Longitudinal strain : The ratio of change in length to original length is called as longitudinal strain.

2) Volume Strain : The ratio of change in volume  to original volume is called as volume strain.

3) Shearing  strain : The ratio of change in shape of a body  to original shape is called as shearing strain.

_{│<<<Stress│   │Hookes Law>>>│} 

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Stress and Strain

Stress and Strain

Introduction : The mechanical properties of any solid depends upon important factor that is stress and strain. Let us discuss this stress and strain in details.

Credit : Photos on unsplash

Stress is defined as ratio of restoring force per unit cross section area.

There are three types of stress 

1) Longitudinal stress :  When the force applied produces change in length of the body, the stress associated is called as longitudinal stress.

Volume Stress : When the force applied produces change in volume of the body, the stress associated is called as volume stress.

Shearing stress : When the force applied produces change in shape of the body, the stress associated is called as shearing stress.

_{│<<<Mechanical Property│   │Strain>>>│} 

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Mechanical Properties of solid

Mechanical Properties of solid

Introduction : In our daily life , we have seen various types of bridges used for crossing a river. We have seen a crane lifting a heavy weight with the help of a thick wire. The beam is used in the construction of various types of houses. Pillars are used for construction of high skyscrapers in modern cities. This is possible only because of mechanical properties of solid.

Photo by Slava Abramovitch on Unsplash

Parameters related to Mechanical properties of solid

Deformation : Change in shape and size of a body is called as deformation.

Deforming Force : The force which bring change in the shape of a body is called as deforming force.

Elasticity: The property of a solid due to which it regains its original shape and size after removal of deforming force is called as elasticity. These material is called as elastic material.

Plasticity :  The property of a solid due to which it can not regains its original shape and size after removal of deforming force is called as plasticity. These material is called as plastic material.

In order to understand Mechanical properties of a body, We must understand the concept of stress and strain.

Stress: Stress is defined as restoring force per unit cross section area. Or Stress can be defined as  force applied per unit cross section area.

Mathematically,

 Stress = Force applied / Cross section area

SI unit of stress is  N/m² or Pascal (Pa)

Dimension : [L^-1 M^-1 T ^-2]

_{│<<<Stress>>>│} 

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Propagation of waves

Propagation of waves

Introduction : Different communication devices that we use in our daily life functions with the help of electromagnetic wave. This electromagnetic waves are transmitted to a large distance to communicate at larger distance. This is possible due to propagation of wave. We are going to see this topic in detail.

Before understanding propagation of waves let us study about Earth's atmosphere.

Propagation of wave : The process of communication involve the process of transmission of wave from one point to another. Transmission or propagation of wave is done mainly through three types.

1) Ground Wave propagation : The transmission of wave through the ground surface is called as ground wave propagation. In this method the wave can be transmitted through very short distance as the radio waves induces current in the ground and looses it's energy  and  thus it is not feasible to transmit it to long distance. This wave has a frequency of  2 MHz. This is used for TV signal and broadcasting.

2) Space Wave propagation : When the radio waves from the transmitting antenna reach the receiving antenna either directly along a straight line (line of sight) or after reflection from the ground or satellite or after reflection from troposphere, the wave propagation is called space wave propagation. TV signals which have high frequency, transmission over long distance is not possible by means of space wave propagation. The maximum distance over which a signal can reach is called its range. 

Mathematically,

Range of Transmission Antenna

 Let the height of the transmitting antenna (AA') situated at A be h. B represents the point on the surface of the Earth at which the space wave hits the Earth. The triangle OA'B is a right angled triangle. From ∆ OA' B we can write

 OA'² = AB'²  + OB2

 (R+h)²  = d²  + R²  or 

R² +  h²   + 2Rh = d²  + R²  

As h << R, we can ignore h²  and write d ≅ √2Rh 

3) Sky Wave propagation : In this type of propagation the wave is transmitted through till receiving antenna after reflection from ionosphere. This method is used to transmit signal to long distance. Mostly waves ranging from 3Mhz to 30MHz is transmitted through sky wave propagation.

 _{│<<<Electromagnetic spectrum│   │Communication System>>>│} 

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Electromagnetic Spectrum

Electromagnetic Spectrum

Introduction : We are surrounded by lots of electromagnetic waves. This waves differ from each other in terms of wavelength and frequency. Thus we have divided this wave into different category according to their wavelength and frequency. We are going to see this in detail.

EM Spectrum
Source: Wikipedia

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The orderly distribution (sequential arrangement) of EM waves according to their wavelengths (or frequencies) in the form of distinct groups having different properties is called the EM spectrum

The variation in wavelength and frequency are shown in table below.

 _{│<<<Electromagnetic waves│   │Wave Propagation>>>│} 

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Electromagnetic waves and communication System

 Electromagnetic waves and communication System

Communication System
Photo by Dušan veverkolog on Unsplash

Introduction :In today's era we have made it possible to communicate with the people at long distance within moment. This is all possible only due to advancement in the field of telecommunication. This communication is possible only with the help of electromagnetic waves. In this chapter we are going to learn more about electromagnetic wave and how this communication is possible with the help of EM Waves.

Electromagnetic Wave
Credit : Vascak.cz

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Electromagnetic waves: The waves which do not require a magnetic medium is called as electromagnetic waves.

Properties of Electromagnetic Waves : 

1) The Electric field E and B are perpendicular to each other and the direction of propagation of wave are also perpendicular to each other.

2) The electromagnetic waves are formed by accelerated charges particles.

3) The  vector product of E and B gives the direction of propagation of wave .

4) The velocity of waves is equal to velocity of visible light which is equal to 3 x 10⁸ m/s.

5) The velocity of waves is given by  c = 1 / √μ₀ε₀ where μ₀= (4π×10^-7 Tm/A) is permeability and ε₀ = (8.85×10^-12C² /Nm²) is permittivity of free space. 

6) The ratio of amplitude of the electric and magnetic field is always constant at a point and  is equal to velocity of the wave.

7) The energy of EM waves is distributed equally between the electric and  magnetic fields. I_E = I_B

 _{│Electromagnetic Spectrum>>>│} 

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Conical Pendulum

Conical Pendulum

Introduction : Conical pendulum is similar to simple pendulum, except the motion it perform. Conical pendulum is given a circular motion. Conical pendulum is a pendulum in which, the metal bob is given circular motion and the string describes a cone.

Conical Pendulum

From the diagram, 

T = tension

h= height

l = slant length 

Ө = elevation angle

mv²/r = Centripetal Force

TsinӨ = Horizontal component of Tension

TcosӨ =Vertical component of Tension

From the above fig,

_{│<<<Uniform Circular  Motion│}    

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Uniform Circular motion

Uniform Circular motion

Introduction: Motion of a particle along the circumference of a circle with constant speed is called as uniform Circular Motion. For performing uniform circular motion, the velocity should have different direction. If acceleration is in line with velocity ,then the magnitude will change and the motion will no loner be a uniform circular motion. For changing direction of velocity there should be an acceleration which should be acting perpendicularly to tangential velocity. As this acceleration is acting towards center, it is called as centripetal acceleration. We will learn more about it in this section.

Uniform Circular Motion

Expression for Centripetal Acceleration : From the diagram shown below

Centripetal acceleration

Consider a circular path with position vector r = OB. The position vector ωt can be resolved into two component, viz 

rcosθ (Horizontal component) and rsinθ (Vertical Component)

r = rcosθ + rsinθ

_{│<<<Projectile Motion│   │Conical Pendulum>>>│} 

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