Physical Optics - Physics- Lecture No-2
Subject: Physics
Topic: Physical Optics
Subject Code: PHY4201
Lecture No: 2
Teacher Name: Md. Rezaul Karim
Topic: Physical Optics
Subject Code: PHY4201
Lecture No: 2
Teacher Name: Md. Rezaul Karim
PHYSICAL OPTICS
Contents
•Basic Properties of Light Wave
•Photon Energy
•Lenses
•Types of Lens
•Terminology of Lens
•Image Location
•Sign Convention
Basic Properties of Light Wave
•Amplitude (a): The vertical distance between the tip of a crest and the wave’s central axis is known as itsamplitude.
•Wavelength (λ): The horizontal distance between two consecutive troughs or crests is known as thewavelengthof the wave.
•Frequency(f)refers to the number of full wavelengths that pass by a given point in space every second; the SI unit for frequency is Hertz(Hz)
•Period (T):
It is the length of time takes for one wave length to pass by a given point in space.
Problem: Calculating wavelength of Light wave
Relationship between wave length and frequency:C=fλ
Relation between Period and frequency: T=1/f
Example 1: A particular wave of electromagnetic radiation has a frequency of 2Х1014 Hz. What is the wavelength of this wave?
Answer: Try yourself
Photon Energy
A photonis the elementary particle, or quantum, of light.
Planck’s Equation, E=hν
where E is the energy of the photon (given in Joules, J),νis frequency of the photon (given in Hertz, Hz), and his Planck’s constant, 6.626×10−34 J⋅s
Example 2: Calculating the energy of a photon
Problem: A photon has a frequency of 2.0×1024 Hz. What is the energy of this photon?
Answer: Try yourself
Lenses
A lens is an image-forming device. It forms an image by refraction of light at its two bounding surface. In general, lens is made of glass.
Types of lenses
1.Convex Lens: A convex lens is a converging lens
since a parallel beam of light, after refraction,
converges to a point, F
2.Concave Lens: A concave lens is a called a diverging
lens since ray coming parallel to the principal axis,
after refraction, diverge out and
seem to come from a point, F.
Convex and Concave Lenses
•A convex lens is thicker at the center than at the edge while a concave lens is thinner at the center than at the edges
Terminology of Lenses
•A lens has two curved surfaces, each surface having a curvature
•The length of radius of curvature of surface is called the radius of curvature, R
•The line joining the centers of curvature of the two curved surfaces is called the principal axis or simply axis of lens.
•The point F to which set of rays parallel to the principal axis is caused to converge (in case of convex lens) or appear to diverge (in case of concave lens) is the principal focus.
•For every lens, there is a point on the principal axis for which the rays passing through it are not deviated by the lens. Any ray passing through it emerges in a direction parallel to the incident ray. Such a point is called optical centre.
•The distance between the focal point F and the optical
center of the lens is called the focal length of the lens.
•The power of a lens is the reciprocal of its focal length (P=1/f)
Image Location (Convex Lens)
Convex Lens
(Table with Images)
Lens Equation
1. 1/𝑣−1/𝑢=(μ−1)(1/𝑅1−1/𝑅2)
If u=α, 1/u=0 and v=f then equation 1 becomes:
2.1/𝑓=(μ−1)(1/𝑅1−1/𝑅2)
Equation 2 is knowns as the lens makers formula, since it enables one to calculate f from the known properties of the lens
3.1/𝑣−1/𝑢=1/𝑓(Comparing equation 1 and 2)
Equation 3 is known as the Gauss formula for lens
Example
•Example 3: A convex lens of focal length 24 cm (μ=1.5) is totally immersed in water (μ=1.33). Find its focal length in water.
•Example 4: Find the focal length of a Plano-convex lens, the radius of the curved surface being 10 cm
In this Lecture Some image and Table. So You have to download for Full Lecture.
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