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# Notes of Ch 4 Electricity| Class 10th Science

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Topics in the Chapter

• Introduction
• Refraction
• Laws of Refraction
→ Snell's law
→ Refractive index
→ Absolute refractive index
→ Optically denser medium
→ Optically rarer medium
→ Spherical lens
• Rules for image formation by convex lens
• Ray diagram of image formed by Convex lens
→ When object is at infinity
→ When object is beyond 2F1
→ When object is at 2F1
→ When object is between F1 and 2F1
→ When object is at F1
→ When object is between F1 and optical centre
• Rules for image formation by concave lens
• Ray diagrams of images formed by a concave lens
→ When object is placed at infinity
→ When object is placed between infinity and optical centre
• Sign convention for spherical lens
→ Lens Formula
→ Magnification
• Power of a lens
Introduction

→ Refraction is bending of light when it enters obliquely from one transparent medium to another.

→ Speed of light is maximum in vaccum. It is 3 × 108 m/s.

→ Cause of refraction: Change in speed of light.

• Some examples of refraction

→ The bottom of swimming pool appears higher.
→ A pencil partially immersed in water appears to be bent at the interface of water and air.

→ Lemons placed in a glass tumbler appear bigger.
→ Letters of a book appear to be raised when seen through a glass slab.

Refraction

→ Bouncing back of light when it strikes on a polished surface like mirror.

→ The extent of bending of ray of light at the opposite parallel faces of rectangular glass slab is equal and opposite, so the ray emerges parallel to incident ray.

• Lateral displacement depends on :
→ Refractive index of glass slab
→ Thickness of the glass slab

Laws of Refraction

(i) The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.

(ii) Snell’s law: The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for a light of given colour and for a given pair of media.

sin i/sin r = constant

Refractive index (n): The ratio of speed of light in a given pair of media
n = Velocity of light in medium 1/Velocity of light in medium 2

→ n21 means refractive index of second medium with respect to first medium.
n21 = v1/v2

→ n12 means refractive index of second medium with respect to first medium.
n12 = v2/v1

Absolute Refractive Index: Refractive index of a medium with respect to vaccum or air.
n = (c/v) x c = 3 × 108 m/s.

→ Refractive index of one medium is reciprocal of other’s refractive index in a given pair.
n12 = 1/n21
→ If refractive index of medium 1 w.r.t. air is given as 1nair, and
If refractive index of medium 2 w.r.t. air is given as 2nair.
Then, refractive index of medium 1 w.r.t. medium 2 = (1nair)/(1nair)
→ Refractive index of diamond is the highest till date. It is 2.42. It means speed of light is 1/2.42 times less in diamond than in vaccum.
• Optically denser medium: Out of two given media, the medium with higher value of refractive index.
• Optically rarer medium: Out of two given media, the medium with lower value to refractive index.
→ When light enters obliquely from a rarer to a denser medium, it bends towards the normal.
→ When light enters obliquely from denser to a rarer medium, it bends away from the normal.
→ Refractive index of a medium does not depend on physical density.
• Spherical lens: A transparent medium bound by two surfaces, of which one or both surfaces are curved.
 Convex Lens Concave Lens Thin from corners Thick from corners Thick at center Thin at centre Converging Diverbging
Rules for image formation by convex lens
(i)  A ray of light parallel to principal axis of a convex lens always pass through the focus on the other side of the lens.
(ii) A ray of light passing through the principal focus will emerge parallel to principal axis after refraction.
(iii) A ray of light passing through the optical center will emerge without any deviation.

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### STD 10 SCIENCE CHAPTER 2 Light – Reflection Class 10th Science MCQ TEST PLAY ONLINE

#### Study Material and Notes of Ch 10 Light – Reflection Class 10th Science

Topics in the Chapter

• Introduction
• Properties of Light
• Reflection
→ Laws of Reflection
→ Virtual and Real image
• Image formed by Plane mirror
→ Characteristics of image formed by Plane mirror
→ Lateral inversion and its application
• Spherical Mirrors
→ Properties of Concave mirror
→ Properties of Convex mirror
→ Common terms for Spherical mirrors
• Rules for making ray diagrams by spherical mirrors
• Ray diagrams for images formed by concave mirror
→ When object is at infinity
→ When object is beyond C
→ When object is at C
→ When object is placed between F and C
→ When object is placed at F
→ When object is between P and F
• Uses of Concave mirror
• Ray diagrams of images formed by convex mirror
→ When object is placed at infinity
→ When object is placed between pole and infinity
• Uses of convex mirror
• Sign convention for reflection by spherical mirror
• Mirror Formula
→ Magnification of Spherical mirrors

Introduction
→ Light is the form of energy that provides sensation of vision.

→ Some common phenomena associated with lights are image formation by mirrors, the twinkling of stars, the beautiful colours of a rainbow, bending of light by a medium and so on.

Properties of Light

→  Electromagnetic wave, so does not require any medium to travel.

→  Light tends to travel in straight line.

→  Light has dual nature i.e. wave as well as particle.

→ Speed of light is maximum in vaccum. Its value is 3 × 108 ms-1.

→ When light falls on a surface, following may happen:
(i) Reflection
(ii) Refraction
(iii) Absorption

Reflection

→ Bouncing back of light when it strikes on a polished surface like mirror.

Laws of Reflection

(i) Angle of incidence is equal to the angle of reflection.

(ii) The incident ray, the reflected ray and the normal at the point of incidence, all lie in the same plane.

Virtual and Real image
Image is a point where atleast two light rays actually meet or appear to meet.
 Real Image Virtual Image Formed when light rays actually meet. Formed when light rays appear to meet. Can be obtained on screen. Can’t be obtained on screen. Inverted Erect Example: image formed on cinema screen and formed by concave mirror. Example: image formed by plane mirror or convex mirror.
Image Formed by Plane Mirror

Characteristics of Image formed by Plane Mirror
(i)  Virtual and erect.
(ii) Size of image is equal to the size of object.
(iii) Image is formed as far behind the mirror as the object is in front of it.
(iv) Laterally inverted.
Lateral Inversion: The right side of the object appears left side of the image and vice-versa.
Application of lateral inversion
→ The word AMBULANCE is written in reverse direction so that it can be read correctly in rear view mirror of vehicles going in front of it.

## Introduction to Nanotechnology: Looking At Nanoparticles

Scientists have been studying and working with nanoparticles for centuries, but the effectiveness of their work has been hampered by their inability to see the structure of nanoparticles. In recent decades the development of microscopes capable of displaying particles as small as atoms has allowed scientists to see what they are working with.
The following illustration titled “The Scale of Things”, created by the U. S. Department of Energy, provides a comparison of various objects to help you begin to envision exactly how small a nanometer is. The chart starts with objects that can be seen by the unaided eye, such as an ant, at the top of the chart, and progresses to objects about a nanometer or less in size, such as the ATP molecule used in humans to store energy from food.
Now that you have an idea of how small a scale nanotechnologists work with, consider the challenge they face. Think about how difficult it is for many of us to insert thread through the eye of a needle. Such an image helps you imagine the problem scientists have working with nanoparticles that can be as much as one millionth the size of the thread. Only through the use of powerful microscopes can they hope to ‘see’ and manipulate these nano-sized particles.

## Introduction to Nanotechnology Applications

The ability to see nano-sized materials has opened up a world of possibilities in a variety of industries and scientific endeavors. Because nanotechnology is essentially a set of techniques that allow manipulation of properties at a very small scale, it can have many applications, such as the ones listed below.
Drug delivery. Today, most harmful side effects of treatments such as chemotherapy are a result of drug delivery methods that don't pinpoint their intended target cells accurately. Researchers at Harvard and MIT have been able to attach special RNA strands, measuring about 10 nm in diameter, to nanoparticles and fill the nanoparticles with a chemotherapy drug. These RNA strands are attracted to cancer cells. When the nanoparticle encounters a cancer cell it adheres to it and releases the drug into the cancer cell. This directed method of drug delivery has great potential for treating cancer patients while producing less side harmful affects than those produced by conventional chemotherapy.
Reactivity of Materials. The properties of many conventional materials change when formed as nano-sized particles (nanoparticles). This is generally because nanoparticles have a greater surface area per weight than larger particles; they are therefore more reactive to some other molecules. For example studies have show that nanoparticles of iron can be effective in the cleanup of chemicals in groundwater because they react more efficiently to those chemicals than larger iron particles.
Strength of Materials. Nano-sized particles of carbon, (for example nanotubes and bucky balls) are extremely strong. Nanotubes and bucky balls are composed of only carbon and their strength comes from special characteristics of the bonds between carbon atoms.  One proposed application that illustrates the strength of nanosized particles of carbon is the manufacture of t-shirt weight bullet proof vests made out of carbon nanotubes.
Micro/Nano ElectroMechanical Systems. The ability to create gears, mirrors, sensor elements, as well as electronic circuitry in silicon surfaces allows the manufacture of miniature sensors such as those used to activate the airbags in your car. This technique is called MEMS (Micro-ElectroMechanical Systems). The MEMS technique results in close integration of the mechanical mechanism with the necessary electronic circuit on a single silicon chip, similar to the method used to produce computer chips. Using MEMS to produce a device reduces both the cost and size of the product, compared to similar devices made with conventional methods. MEMS is a stepping stone to NEMS or Nano-ElectroMechanical Systems. NEMS products are being made by a few companies, and will take over as the standard once manufacturers make the investment in the equipment needed to produce nano-sized features.
Molecular Manufacturing. If you're a Star Trek fan, you remember the replicator, a device that could produce anything from a space age guitar to a cup of Earl Grey tea. Your favorite character just programmed the replicator, and whatever he or she wanted appeared. Researchers are working on developing a method called molecular manufacturing that may someday make the Star Trek replicator a reality. The gadget these folks envision is called a molecular fabricator; this device would use tiny manipulators to position atoms and molecules to build an object as complex as a desktop computer. Researchers believe that raw materials can be used to reproduce almost any inanimate object using this method.
UNIT TEST OF NENO TECHNOLOGY

## 17 August 2018

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Community Helpers are people in professions that directly impact the lives of others. They deliver a service that makes our lives easier. It is important for all of us to know the ways in which Community Helpers work. We can also help them do their jobs better if we understand the role they play. In many ways community helpers remind us of how inter-connected our lives are.
Many community helpers have easily identifiable work attire or clothes. This makes it easy to know their role in the community and is helpful if you need to approach them for help. A policeman or fire fighter’s uniform and a doctor’s coat thus become important clues of what they can do. Some community helpers also have identifiable means of transport e.g. the police car, the fire truck the mail van, the ambulance etc.
Children of Class 1 had an activity in which they dressed up as Community Helpers belonging to different professions. They enacted their roles with realistic props alongwith appropriate words.
This activity will help to instill in them respect for all professions and learn to value them better.