PHYSICS_LEARNING MATERIAL_2022 Sem 2 final

Haryana State Board of Technical Education - Physics Diploma 2nd Semester (Feb, 2023)

Preface

• Technical education in polytechnics is vital for human resource development, creating skilled manpower, enhancing industrial productivity, and improving quality of life.
• Polytechnic education aims to create a skill-based workforce, bridging technicians and engineers.
• Diploma holders are preferred by small and medium-scale industries for their skills in reading drawings, estimating, costing, billing, supervision, measurement, testing, repair, and maintenance.
• Challenges include the quality of education and students from rural backgrounds facing difficulty understanding technical content in English.
• The Haryana State Board of Technical Education focuses on ensuring quality technical education, designing need-based diploma programs, and developing tailored learning material.
• Learning Text Booklet provides standard material for teachers and students.

Team Involved in Development

• Dr. Bhajan Lal, Senior Lecturer Physics, Govt. Polytechnic Dhangar, Fatehabad
• Dr. Sarita Maan, Lecturer Physics, Govt. Polytechnic, Ambala City
• Sh. Anil Nain, Senior Lecturer Physics, Govt. Polytechnic, Hisar
• Smt. Bindu Verma, Lecturer Physics, SJPP Damla

Index

• Chapter 1: Wave Motion and Its Applications (1-11)
• Chapter 2: Optics (12-21)
• Chapter 3: Electrostatics and Electricity (22-36)
• Chapter 4: Classification of Materials and Their Properties (37-46)
• Chapter 5: Modern Physics (47-55)
• Sample Papers (56-61)

Distribution of Syllabus and Marks (200023) Applied Physics Semester-II

• Rationale: Applied physics includes diverse topics related to the world around us, focusing on observation and prediction of object behavior.
• Concrete use of physical principles and analysis in engineering and technology is emphasized.
• Teachers should provide engineering/technology applications of concepts and principles.
• SI units should be followed.
• Learning Outcomes:
  • Differentiate between transverse and longitudinal waves, periodic and simple harmonic motion.
  • Explain frequency, amplitude, wavelength, wave velocity, and their relationships.
  • Explain laws of reflection and refraction of light.
  • Explain total internal reflection as applied to optical fibers.
  • Define capacitance and its unit.
  • Explain the role of free electrons in insulators, conductors, and semiconductors.
  • Explain electric current as flow of charge, the concept of resistance; calculate equivalent resistance of resistor combinations.
  • Understand the concept of magnetism and type of magnetic materials
  • Describe the Laser and its applications
  • Learn about optical fibre and wave propagation in it
  • Define nanotechnology and properties of nonmaterial

1. Wave motion and its applications

• 1.1 Waves: definition, types (mechanical and electromagnetic wave)
• 1.2 Wave motion- transverse and longitudinal with examples, terms used in wave motion like displacement, amplitude, time period, frequency, wavelength, wave velocity; relationship among wave velocity, frequency and wave length
• 1.3 Simple harmonic motion (SHM): definition, examples
• 1.4 Cantilever: definition, formula of time period (without derivation)
• 1.5 Free, forced and resonant vibrations with examples
• 1.6 Sound waves: types (infrasonic, audible, ultrasonic) on the basis of frequency, noise, coefficient of absorption of sound, echo

2. Optics

• 2.1 Reflection and refraction of light with laws, refractive index
• 2.2 Lens: introduction, lens formulae (no derivation), power of lens and simple numerical problems
• 2.3 Total internal reflection and its applications, critical angle and conditions for total internal reflection
• 2.4 Superposition of waves (concept only), definition of Interference, Diffraction and Polarization of waves
• 2.5 Introduction to Microscope, Telescope and their applications

3. Electrostatics and Electricity

• 3.1 Electric charge, unit of charge, conservation of charge
• 3.2 Coulomb’s law of electrostatics
• 3.3 Electric field, electric lines of force (definition and properties), electric field intensity due to a point charge
• 3.4 Definition of electric flux, Gauss law (statement and formula)
• 3.5 Capacitor and capacitance (with formula and unit)
• 3.6 Electric current and its SI Unit, direct and alternating current
• 3.7 Resistance, conductance (definition and unit)
• 3.8 Series and parallel combination of resistances
• 3.9 Ohm’s law (statement and formula)

4. Classification of Materials and their Properties

• 4.1 Definition of energy level, energy bands
• 4.2 Types of materials (conductor, semiconductor, insulator and dielectric) with examples, intrinsic and extrinsic semiconductors (introduction only)
• 4.3 Introduction to magnetism, type of magnetic materials: diamagnetic, paramagnetic and ferromagnetic materials with examples
• 4.4 Magnetic field, magnetic lines of force, magnetic flux
• 4.5 Electromagnetic induction (definition)

5. Modern Physics

• 5.1 Laser: introduction, principle, absorption, spontaneous emission, stimulated emission, population inversion
• 5.2 Engineering and medical applications of laser
• 5.3 Fibre optics: introduction to optical fibers (definition, principle and parts), light propagation, fiber types (mono-mode, multi-mode), applications in medical, telecommunication and sensors
• 5.4 Nanotechnology: introduction, definition of nanomaterials with examples, properties at nanoscale, applications of nanotechnology (brief)

LIST OF PRACTICALS (08 experiments are compulsory)

1. Familiarization with apparatus (resistor, rheostat, key, ammeter, voltmeter, telescope, microscope etc)
2. To find the time period of a simple pendulum.
3. To study variation of time period of a simple pendulum with change in length of pendulum.
4. To determine and verify the time period of Cantilever.
5. To verify Ohm’s laws by plotting a graph between voltage and current.
6. To study colour coding scheme of resistance.
7. To verify laws of resistances in series combination.
8. To verify laws of resistance in parallel combination.
9. To find resistance of galvanometer by half deflection method.
10. To verify laws of reflection of light using mirror.
11. To verify laws of refraction using glass slab.
12. To find the focal length of a concave lens, using a convex lens.

INSTRUCTIONAL STATREGY

• Teacher may use various teaching aids like models, charts, graphs and experimental kits etc. for imparting effective instructions in the subject.
• Students need to be exposed to use of different sets of units and conversion from one-unit type to another. Software may be used to solve problems involving conversion of units.
• The teacher should explain about field applications before teaching the basics of mechanics, work, power and energy, rotational motion, properties of matter etc. to develop proper understanding of the physical phenomenon. Use of demonstration can make the subject interesting and develop scientific temper in the students.

MEANS OF ASSESSMENT

• Assignments and quiz/class tests, and end-term written tests, model/prototype
• Actual laboratory and practical work, exercises and viva-voce

RECOMMENDED BOOKS

1. Text Book of Physics for Class XII (Part-I, Part-II); N.C.E.R.T., Delhi
2. Applied Physics, Vol. I & II by Dr. HH Lal; TTTI Publications, Tata McGraw Hill, Delhi
3. Applied Physics -II by AS Vasudeva; Modern Publishers, Jalandhar.
4. Applied Physics - II by R A Banwait; Eagle Prakashan, Jalandhar.
5. A text book of OPTICS by N Subrahmanyam, Brij Lal and Avadhanulu; S Chand Publishing, New Delhi.
6. e-books/e-tools/relevant software to be used as recommended by AICTE/ HSBTE/ NITTTR.
7. Nanotechnology: Importance and Applications by M H Fulekar; IK International Publishing House (P) Ltd., New Delhi.
8. Practical Physics, by C. L. Arora, S Chand Publication

• Websites for Reference: http://swayam.gov.in

Chapter 1 - Wave Motion and Its Applications

Learning Objectives:

• Understand waves and wave motion, define parameters, and their relationships; define simple harmonic motion (SHM).
• Understand vibrations and vibration types.
• Describe acoustics, parameters, and methods to control building acoustics.
• Identify ultrasonic waves and list engineering applications.

1.1 WAVE MOTION

• Motion is the change in an object's position with time, transporting energy.
• Energy transportation:
  • Actual transport of matter (e.g., bullet).
  • Wave process.
• A wave is a disturbance transferring energy through repeated periodic motion of medium particles.
• Waves carry energy but do not transport matter.
• Two types of waves:
  • Mechanical or Elastic waves
  • Electromagnetic waves

Mechanical Waves

• Produced by repeated periodic motion of medium particles.
• Require a material medium for generation and propagation.
• Examples: sound waves, water waves.

Electromagnetic Waves

• Travel as varying electric and magnetic fields, mutually perpendicular to each other and the direction of propagation.
• Do not need a material medium.
• Examples: light waves, heat radiations, radio waves, X-rays.

Characteristics of Wave Motion:

1. Wave travels forward; particles vibrate about their mean position.
2. Wave velocity is the rate at which the disturbance travels through the medium.
3. Wave velocity depends on the wave type and medium type.
4. Wave velocity differs from particle velocity.
5. Regular phase difference between particles.

1.2 Types of Wave Motion

Two types of wave motion:

• Transverse wave motion
• Longitudinal wave motion

a) Transverse Wave Motion

• Particles vibrate perpendicular to the direction of wave propagation.
• Consists of one crest and one trough per cycle.
• Wavelength: Distance between two consecutive crests or troughs.
• Examples: waves on a stretched string, light waves, water surface waves

b) Longitudinal Waves

• Particles vibrate parallel to the direction of wave propagation.
• Travels in compressions and rarefactions.
• Compression: Particles closer than normal.
• Rarefaction: Particles farther than normal.
• One cycle includes one compression and one rarefaction.
• Wavelength: Distance between two consecutive compressions or rarefactions.
• Most familiar example: sound waves, which travel in solids, liquids, and gases.

Difference between Transverse and Longitudinal Waves

Terms Characterizing Wave Motion

• Displacement: Distance of a particle from its mean position at any instant.
• Amplitude: Maximum displacement from the mean position.
• Wavelength ($\lambda$): Distance traveled by the wave in one vibration or cycle; distance between two consecutive crests or troughs, measured in meters (m).
• Time period (T): Time for a wave to complete one vibration or cycle, in seconds (s).
• Frequency ($\nu$): Number of vibrations per second, reciprocal of time period (\nu = \rac{1}{T}), in hertz (Hz).
• Wave Velocity (v): Distance traveled by the wave per unit time, in meters per second (m/s).
• Phase ($\theta$): Position of a particle at an instant, measured by fraction of angle or time since crossing mean position in the positive direction, in radians.
• Phase difference ($\phi$): Difference in angle or time between two particles at any instant.
  • Calculated by the formula: $\text{Phase difference } (\phi) = \frac{2 \pi}{\lambda} \times \text{path difference}$

Relation between Wave velocity, Wavelength and Frequency

• Wave velocity is the distance traveled by a wave in one time period.
• Frequency is the reciprocal of time period ($\nu = \frac{1}{T}$).
• $v = \nu \lambda$
• This relation holds for both transverse and longitudinal waves.

Numerical 1:

• A radio station broadcasts at a frequency of 15 MHz. The velocity of transmitted waves is $3 \times 10^8$ m/s. What is the wavelength of transmitted waves?
• Solution:
  • Given: $\nu = 15 \times 10^6 \text{ Hz}$, $v = 3 \times 10^8 \text{ m/s}$
  • Using $v = \nu \lambda$, $\lambda = \frac{v}{\nu} = \frac{3 \times 10^8}{15 \times 10^6} = 20 \text{ m}$

Numerical 2:

• A tuning fork of frequency 512 Hz makes 24 vibrations in air. If velocity of sound in air is 340 m/s, how far does sound travel in air?
• Solution:
  • Given: $\nu = 512 \text{ Hz}$, $v = 340 \text{ m/s}$
  • Using $v = \nu \lambda$, $\lambda = \frac{v}{\nu} = \frac{340}{512} = 0.664 \text{ m}$
  • Distance in 24 vibrations $= 24 \times \lambda = 24 \times 0.664 = 15.94 \text{ m}$

1.3 SIMPLE HARMONIC MOTION (SHM)

• Restoring force is directly proportional to displacement from the mean position.
• Applying Newton’s second law (F = ma), $F = -Ky$ or $a = -\frac{K}{m} y$, where K is force constant.
• Displacement varies harmonically: $y(t) = A \sin(\omega t)$ or $A \cos(\omega t)$, where A is amplitude, $\omega$ is angular frequency.
• Examples: simple pendulum, cantilever, mass-spring system, swing.

Characteristics of SHM:

• Periodic motion.
• Force directed toward the equilibrium point.
• Acceleration is directly proportional to displacement from equilibrium.

1.4 CANTILEVER

• A metallic beam fixed at one end and free to vibrate at the other.
• Time period: $T = 2\pi \sqrt{\frac{p}{g}}$, where p is the depression of the beam and g is acceleration due to gravity.

1.5 FREE, FORCED AND RESONANT VIBRATIONS

• Vibration: To and fro motion about mean position (oscillatory motion).
• Periodic Motion: object repeats its path after a fixed or regular interval of time.

Types of Vibrations:

• Free, forced, and resonant.

1) Free Vibrations

• Object vibrates freely under its own elastic forces.
• Frequency of free vibration is called natural frequency.
• Examples: vibrations of simple pendulum, cantilever, loaded beam.

a) Damped Vibrations:

• Amplitude decreases with time.
• Due to loss or dissipation of energy over time.
• Examples: vibrations of cantilever, spring mass system.

b) Undamped Vibrations:

• Amplitude remains constant; vibrations continue indefinitely.
• Example: vibrations of a simple pendulum in a vacuum.

2) Forced Vibrations

• When periodic force maintains the vibrations of an object.
• Example: swing of a child.

3) Resonant Vibrations

• Frequency of applied force matches object's natural frequency.
• Amplitude increases largely.
• Examples:
  • Tuning of a radio set.
  • Collapse of certain buildings during earthquake (due to matching natural frequency).

1.6 SOUND WAVES

• Mechanical waves that need a medium for propagation.
• Categories by frequency:
  • Audible (20 Hz - 20 kHz).
  • Infrasonic (below 20 Hz): produced and used by animals like elephants.
  • Ultrasonic (above 20 kHz): used by bats.

Properties of Sound Waves:

1. Longitudinal mechanical waves.
2. Need material medium.
3. Cannot travel through vacuum.
4. Velocity in air at NTP is 332 m/s (increases with temperature).
5. Travel faster in solids than in liquids and gases.
6. Exhibit reflection, transmission, diffraction.

Types of Audible Sound:

Musical Sound

• Pleasant effect on ears.
• Single or multiple sounds having same frequency and wavelength, meeting in same phase. E.g. music

Noise

• Unpleasant effect on ears.
• Irregular patterns of amplitude and frequency. E.g. horn, thunder.

Coefficient of Absorption of Sound:

• Ratio of sound energy absorbed by a surface to the total sound incident on the surface.
• Denoted by ‘a,’ SI unit is OWU (open window unit).
• $a = \frac{\text{absorbed sound energy by a surface}}{\text{Total sound energy incident on the surface}}$
• Maximum value (=1) for an open window.

Echo:

Repetition of original sound by reflection.

• Produced if reflected sound reaches ears after 1/10 of a second.
• Different from reverberation due to time gap.
• $d = \frac{v \cdot t}{2}$, where 'v' is velocity, 't' is time taken.
• Minimum distance of obstacle to produce echo is 16.6 m.

Numerical 3:

• An ultrasonic scanner travelling with a speed of 1.5 km/s in a tissue operating under a frequency of 4.1 MHz. What is the wavelength of sound in the tissue?
• Solution:
  • Given: $v = 1.5 \text{ km/s} = 1500 \text{ m/s}$, $\nu = 4.1 \text{ MHz}= 4.1 \times 10^6 \text{ Hz}$
  • $v = \nu \lambda \implies \lambda = \frac{v}{\nu} = \frac{1500}{4.1 \times 10^6} = 3.65 \times 10^{-4} \text{ m} = 36.5 \mu m$

Numerical 4:

• A man hears his sound again after reflection from a cliff after 1 second. If the velocity of sound is 330 m/s, find the distance of cliff from the man.
• Solution:
  • Given: $v = 330 \text{ m/s}$, $t = 1.0 \text{ s}$
  • $2d = v \times t = 330 \times 1 = 330 \text{ m}$, $d = 165 \text{ m}$

Chapter 2 OPTICS

Learning Objectives:

• Understand light properties, reflection and refraction of light, lens parameters, lens formula, and power of a lens.
• Explain total internal reflection (TIR), conditions for TIR, and its applications.
• Describe microscopes, telescopes, and their uses.

Introduction

• Optics is the branch of physics that studies the behavior and properties of light.
• Light is an electromagnetic wave having transverse nature.
• Light has dual nature; particle as well as wave
• Classical approach considers only wave nature.
• Wave nature is simplified in geometric optics, where light is treated as a ray which travels in straight line.
• Ray optics model includes wave effects like diffraction, interference
• Quantum optics deals with application of light considered as particles (called photons) to the optical systems.
• Phenomena like photoelectric effect, X-rays, and lasers are explained in quantum optics (particle nature of light).

Ray Optics (Geometric optics)

• Geometric optics describes the propagation of light in terms of rays.
• Assumptions of geometrical optics:
  • Light travels in straight-line paths.
  • It bends, or split into part, at the interface between two different media.
  • It follows curved paths in a medium where refractive index changes.
  • It may be reflected, absorbed or transmitted.

2.1 REFLECTION AND REFRACTION OF LIGHT

REFLECTION OF LIGHT

• Phenomena of bouncing back of light after striking at a polished surface.
• Glassy surfaces such as mirrors exhibit reflection.

Laws of reflection:

1. The incident ray, reflected ray and the normal, all lie in same plane.
2. The angle of incidence is always equal to angle of refraction i.e. $$\thetai = \thetar

REFRACTION OF LIGHT

• When a light ray passes from one transparent medium to another, it gets deviated from its original path.
• Bending of light rays from their original path while passing from one medium to another is called refraction.
• When light travels from a rarer medium to denser medium, it bends towards the normal.
• When light travels from a denser medium to rarer medium, it bends away from the normal.
• Refraction occurs due to change in speed of light as it enters a different media.

Laws of refraction:

1. The incident ray, the refracted ray and the normal all lie in the same plane.
2. The ratio of sine of incidence angle (\theta1$) to the sine of refracted angle ($\theta2) is a constant for that pair of media and is equal to the refractive index of that media. This is also known as Snell’s law
   • \frac{\sin \theta1}{\sin \theta2} = \mu{21} $, where$\mu{21} is the refractive index of medium 2 w.r.t. medium 1.
   • If medium 1 is vacuum then, \mu = \frac{c}{v}, where c is the velocity of light in air (vacuum) and v is the velocity of light in the medium.
   • Refractive index of water is 1.333, meaning that light travels 1.333 times slower in the water than in vacuum.
   • Refractive index is a dimensionless number.

Snell’s law is used to find the deflection of light rays when they pass through different media. It is used to produce dispersion spectra through a prism since light ray having different frequencies have slightly different refractive index in most materials.

2.2 LENS AND LENS FORMULA

• Lens is an optical device based on phenomenon of refraction.
• A lens is a transparent medium bounded by two refracting surfaces.
• It can produce two types of rays- converging and diverging rays.
• Convex lens is converging while concave lens is diverging.

Terms related in study of lenses:

1. Centre of curvature: The center of curvature of a lens is the centre of sphere which forms a part of the spherical surface of the lens.
2. Radius of curvature: The radius of the sphere of the spherical surface of lens is called radius of curvature.
3. Principal axis: The principal axis of a lens is an imaginary line that is perpendicular to the vertical axis of the lens.
4. Optical centre: Optical centre is the centre of the lens lying on the principal axis. If a light ray passes through optical centre, it goes undeviated.
5. Principal focus: When the parallel rays are incident on a lens, they either meet or appear to meet at a point on the principal axis, that point is called principal focus.
6. Focal length (f): The distance of principal focus from the optical centre is called focal length. In other words, focal length is equal to the image distance when the object is at infinity.
7. Image: If two or more rays passing from a point gets refracted through a lens and converges or appears to diverge to a point then that point is called the image of first point. The image can be real or virtual. In real image, rays actually meet at the second point, while in virtual image; the rays appear to diverge from the second point.

LENS FORMULA

• The formula which gives relation between focal length (f), object distance (u) and image distance (v):
  • \frac{1}{f} = \frac{1}{v} - \frac{1}{u} (Lens formula)

Linear magnification:

• The ratio of size of image to the size of object
  • m = \frac{I}{O} = \frac{v}{u}

POWER OF LENS

• The ability of a lens to converge or diverge the light rays.
• Power of a lens is defined as the reciprocal of the focal length. (f is taken in metre)
  • P = \frac{1}{f}
• The unit of power of lens is m-1 which is called dioptre and indicated by symbol ‘D’.
• In other words, one dioptre is the power of a lens of one metre focal length.
• The power of a convex lens is positive and that of concave lens is negative.
• If two lenses are combined (placed in contact), the focal length of the combination is given by \frac{1}{F} = \frac{1}{f1} + \frac{1}{f2} $. Thus the power of combination becomes sum of power of individual lenses. i.e.$ P = P1 + P2 $. In general,$ P= P1 + P2+ P_3 + ……….

2.3 TOTAL INTERNAL REFLECTION (TIR)

• When light goes from denser medium to rare medium and the angle of incidence is greater than critical angle, the light get completely reflected in the same medium.

• Two essential conditions for TIR:

  1. The light should travel from denser medium to rarer medium.
  2. The angle of incidence in the denser medium should be greater than the critical angle.

• The angle of incidence for which the angle of refraction becomes 90° is called as critical angle (\theta_c). At the critical angle of incidence, the refracted ray travels along the boundary between the two media i.e. the angle of refraction becomes 900. For angle of incidence greater than critical angle light is totally reflected

• The critical angle for a material depends upon the refractive index. Higher the refractive index, the lower the critical angle.

  • \sin \thetac = \frac{1}{\mu} $, where$\thetac is the critical angle and μ is the refractive index.

Applications of TIR

1. TIR is the basic principle of optical fibers which are used as transmission media in sending telecommunication signals and images in endoscopes.
2. Automotive rain sensors work on the principle of TIR, which control automatic windscreen wipers.
3. Prisms in binoculars also form erect images based on total internal reflection.
4. Some multi-touch screens also use TIR to pick up multiple targets.
5. Optical fingerprinting devices used to record fingerprints without the use of ink are also based on TIR.
6. The bright shining of diamonds is also a result of total internal reflection.
7. Formation of mirage.

2.4 SUPERPOSITION OF WAVES- INTERFERENCE, DIFFRACTION AND POLARIZATION OF WAVES

• According to the superposition principle, when a number of waves are interacting, the resultant displacement at a particular point is the vector sum of the individual displacements produced by each of the waves at that point. The resultant wave has properties of both the waves.
• Formation of beats, standing waves are examples of superposition of waves.
• An interference is caused due to superposition of waves.

INTERFERENCE:

• The formation of maximum intensity at some points and minimum intensity at some other point when two (or) more waves of equal frequency having constant phase difference meet at a point simultaneously, superimpose with each other.
• Interference is of two types.

Types of interference:

• If two waves which superimpose with each other are in the same phase, the amplitude of the resultant is equal to the sum of the amplitudes of individual waves resulting in the maximum intensity of light, this is known as constructive interference.
• If the crests of one wave coincide with the crests of the other, the amplitudes are additive.

• If two waves superimpose with each other in opposite phase, the amplitude of the resultant is equal to the difference in amplitude of individual waves, resulting in the minimum intensity of light, this is known as destructive interference.

DIFFRACTION:

• The spreading of waves as they pass through an aperture or obstacle.
• It occurs when the size of aperture or obstacle is of same order of magnitude as the wavelength of incident wave.
• The amount of bending depends on the relative size of the opening compared to the wavelength of light.

POLARIZATION OF LIGHT:

• A light wave that is vibrating in more than one plane is referred to as unpolarised light.
• Light waves are created by electric charges that vibrate in a variety of directions, thus creating an electromagnetic wave that vibrates in a variety of directions.
• Polarized light waves are light waves in which the vibrations occur in a single plane.
• The process of transforming unpolarised light into polarized light is known as polarization. Polarizer or Polaroid is used to make an unpolarised light into polarized

2.5 OPTICAL INSTRUMENTS

• An optical instrument is a device which is used to view the objects. The eye is natural optical system. In addition to it, other instruments are devised to increase the range a human’s viewing ability.
• The optical instruments are an aid to the eye. They consist of an arrangement of lenses, prisms or mirrors which enables to see better than what we can see with the naked eye.

a) Microscope:

• A microscope is an optical instrument which enables us to see magnified image of very small objects.
• A microscopic object is invisible to the eye unless aided by a microscope.
• Types of microscope:
  1. Simple microscope. It is also known as magnifying glass.
  2. Compound microscope. To produce large magnification, a compound microscope is used in which magnification is obtained in two stages by the use of two convex lenses.

Telescope:

• A telescope is an optical instrument which is used to see distant objects clearly.
  1. Astronomical: It is used to see astronomical heavenly objects like stars and planets. The image formed in an astronomical telescope is inverted.
  2. Terrestrial: Forms an erect image and makes use of three convex lenses.
  3. Galilean (modification of terrestrial telescope): It is a modified version of terrestrial telescope which also forms erect image but with the use of only two lenses.

USES OF MICROSCOPE

1. Biological scientists use microscope to see microorganisms and their behavior.
2. Doctors use microscope to see and examine blood cells and bacteria.
3. Forensic science experts use microscope to analyze the evidences of crimes.
4. Jewelers and watch makers use it to see the details of parts they are working with.
5. Environmentalist uses it to test the soil and water samples for presence of pollutants.
6. Geologist uses it to test the composition of different types of rocks.
7. These are used in various laboratories.

USES OF TELESCOPE

1. Astronomical objects are seen by using telescope by astronomers.
2. They found use in terrestrial applications also. They are used in laboratories to perform different experiments and finding values of different quantities.
3. Spectrometry uses telescopes to find wavelength of light and spectral lines etc.
4. It is used in spy glasses and long focus camera lenses.

Solved Numerical

Numerical 1.

• A lens is having power of +4 D. What is its focal length?
• Solution:
  • Given, Power (P) = +4 D
  • We know that P = \frac {1}{f} $, Therefore,$ \4 = \frac {1}{f} $or$ f = \frac {1}{4} = 0.25 m = 25 cm
  • Thus, focal length of lens is 25 cm.

Numerical 2.

• An object is kept at distance of 30 cm from a convex lens of focal length 0.2 m. Find the position of the image formed.
• Solution:
  • Given, distance of object, u = - 30 cm = - 0.3 m, and f = 0.2 m
  • The lens formula is \frac {1}{f }= \frac {1}{v} - \frac {1}{u}
  • \frac {1}{v } = \frac {1}{f} + \frac {1}{u} = \frac {1}{0.2} - \frac {1}{0.3} = 5-3.33 = 1.67
  • v = \frac {1}{1.67} = 0.598 = 0.6 m = 60 cm

Numerical 3.

• A light wave has wavelength of 600 nm in vacuum. What is the wavelength of the light as it travels through water (index of refraction = 1.33)?
• Solution:
  • Given, wavelength (λ) = 600 nm = 600 ×10-9 m ( 1 nm = 10-9 m).
  • The wavelength of light that travels through a medium of refractive index n changes by expression
  • λ_n = \frac{λ}{n}= \frac{600 \times 1