## Rules for Image Formation by Ray Diagram

### Rules for image formation from concave mirror

When the light ray incident parallel to the principal axis.

OR

When the light ray incident towards focus.

When the light ray incident on the pole of the mirror.

Read Also : Important Rule of Light Reflection

### Rules for image formation from convex mirror

When the light ray incident parallel to the principal axis.

OR

When the light ray incident parallel to the principal axis

When the light ray incident on the mirror directing towards centre of curvature.

### Sign convention

Description : It is a convention which fixes the signs of different distances measured. The sign convention to be followed is the New Cartesian sign convention. It gives the following rules :

1. All distances are measured from the pole of the mirror.
2. The distances measured in the same direction as the direction of incident light from pole are taken as positive.
3. The distances measured in the direction opposite to the direction on incident light from pole are taken as negative.
4. Distances measured upward and perpendicular to the principal axis, are taken as positive.
5. Distances measured downward and perpendicular to the principal axis, are taken as negative.

Read Also : Reflection from Spherical Mirror

## Reflection from spherical mirror

Introduction : There are two types of spherical mirrors:

(i)   Concave mirror :

(ii) Convex mirror :

### Some terms associated with spherical mirrors.

Aperture. The diameter of the circular rim of the mirror. In diagram AB is the aperture of the mirror.

Pole : The centre of the spherical surface of the mirror is called the pole of the mirror. It lies on the surface. In diagram, P is the pole of the mirror.

Centre of curvature : The Centre of the spherical shell, of which the mirror is a section, is called center of curvature of the mirror. It lies outside the surface. Every point on mirror surface lies at same distance from it. In diagram, C is the centre of curvature of the mirror.

Principal axis : The straight line passing through the pole and the center of curvature of the mirror, is called principal axis of the mirror.

Principal focus : It is a point on the principal axis of the mirror, such that the rays incident on the mirror parallel to the principal axis after reflection, actually meet at this point (in case of a concave mirror) or appear to come from it (in case of a convex mirror). In diagram, F is the principal focus of the mirror.

Radius of curvature : The distance between the pole and the Centre of curvature of the mirror, is called the radius of curvature of the mirror. It is equal to the radius of the spherical shell of which the mirror is a section. In diagram, PC is the radius of curvature of the mirror. It is represented by the symbol R.

Focal length : The distance between the pole and principal focus of the mirror, is called the focal length of the mirror. In diagram, PF is the focal length of the mirror. It is represented by the symbol f.

f=+R2

for convex

f=-R2

for concave

Principal section : A section of the spherical mirror cut by a plane passing through its centre of curvature and the pole of the mirror, is called a principal section of the mirror. It contains the principal axis. In diagram, APB is the principal section of the mirror cut by the plane of the book page.

Read Also : Important Point of Light Reflection

## BEST MOBILE UNDER 20000

### Best Phone Under 20000

In the era of technology, everyday so many things being transformed with new technologies. Mobile phones are one of them. Every month you get more than 100 of mobile phones launched worldwide. But nobody buy all these devices and people select one of them according to their requirement and usage. Customer also take care of budget as well as features. In single word customer wants a device or mobile in low budget and best features. So we are going to help the people to and advice 10 Best Mobile under 20000 Indian Rupee.

### 1. Redmi K20

Redmi K20 is first flagship phone of K series Redmi tried to compete mid range budget phone and with little high price Redmi K20 is perfect mobile for users who want good processor, pop up selfi camera and super amoled display. Redmi K20 is also protected by gorilla glass. It’s processor make it best mobile under 20000 price

#### Features of Redmi K20

RAM & Storage: 6GB + 64GB, 6GB + 128

Camera : 48MP + 13MP + 8MP | 20MP Front Camera

Battery : 4000 mAh Battery

Processor : Qualcomm Snapdragon 730 Processor

Display : 16.23 cm (6.39 inch) Full HD+ Amoled Display

### 2. Realme X

Realme is biggest competitor of Redmi and always try to give things better than xiaomi. Realme X is also a flagship phone of Realme. Realme X also have powerful Qualcomm Snapdragon 710 Octa Core 2.2 GHz AIE Processor but less than Redmi K20 and Realme 2 is 2nd Best mobile under 20000 in India.

Realme X have only one storage variant of 128 GB and two Ram variants available.

#### Features of Realme X

RAM & Storage: 4GB + 128GB, 8GB + 128GB

Camera : 48MP + 5MP | 16MP Front Camera

Battery : 3765 mAh Battery

Processor : Qualcomm Snapdragon 710 Octa Core 2.2 GHz AIE Processor

Display : 16.59 cm (6.53 inch) Full HD+ Display

### 3. Realme XT

Realme XT is best mobile under 20000. If we are talking about Realme XT features its fully loaded with strong Qualcomm 712 Processor  and powerful camera setup. Realme XT have in display finger print with super amoled display which shows the color very bright and punchy.

Realme XT also have quad camera with 64 megapixel capacity which really capture fabulous images.

#### Features of Galaxy M30S

RAM & Storage: 4 GB RAM | 64 GB ROM | Expandable Upto 256 GB

Camera : 64MP + 8MP + 2MP + 2MP Quad Camera | 16MP Front Camera

Battery : 4000 mAh Battery

Processor : Qualcomm 712 Processor

Display : 16.26 cm (6.4 inch) Display

### 4. Vivo Z1 Pro

Vivo Z1 pro is packed phone with huge battery and powered by the Qualcomm Snapdragon 712 AIE processor. It is first phone with this processor in India under 15000 price. Some feature like amoled display is missing but viewing quality is good and in this budget its a perfect phone.

#### Features ofVivo Z1 Pro

RAM & Storage : 4GB + 64GB, 6GB + 64GB & 6GB + 128GB

Camera : 16MP + 8MP + 2MP | 32MP Front Camera

Battery : 5000 mAH Battery

Processor : Qualcomm Snapdragon 712 AIE Octa Core 2.3GHz Processor

Display : 6.53 inch FHD+ Display

### 5. Nokia 8.1

Nokia 8.1 is successor of Nokia 7.1 with improved processor and better camera setup. Nokia 8.1 have extra 500 mAh battery than Nokia 7.1 and display also improved and with Full HD+ Display. Nokia 8.1 have Qualcomm Snapdragon 710 Processor.

If you want pure android experience and also love Nokia phones than Nokia 8.1 is best phone under 15000 for you.

#### Features of Nokia 8.1

RAM & Storage : 4 GB + 64 GB

Camera : 12MP + 5MP | 8MP Front Camera

Battery : 3500 mAH

Processor : Qualcomm Snapdragon 710 Processor

Display : 15.7 cm (6.18 inch) Full HD+ Display

### 6. Realme 3 Pro

Realme 3 pro is one of the best low budget phone it competites phones under 15000. It has Android Pie v9.0 operating system with 2.2GHz Qualcomm Snapdragon 710 AIE octa core processor.

#### Features of Realme 3 Pro

RAM & Storage : 4 GB + 64 GB & 6 GB + 128 GB

Camera : 16MP+5MP dual rear camera | 25MP front camera

Battery : 4000 mAH

Processor : Snapdragon 710 AIE octa core processor

Display : 6.3 inch FHD+ IPS Display

### 7. Redmi Note 7 Pro

Xiomi Redmi is very popular mobile phone company in india and Note series has a credit of this popularity. Redmi Note 7 Pro is also one of them. Redmi Note 7 Pro has a great built quality with 48 Megapixel camera gorilla glass protection. Powerful processor of Snapdragon 675 make it fast.

#### Features of Redmi Note 7 Pro

RAM & Storage : 4 GB + 64 GB & 6 GB + 64 or 128 GB

Camera : 48MP + 5MP | 13MP Front Camera

Battery : 4000 mAH

Processor : Qualcomm Snapdragon 675 Processor

Display : FHD+ IPS Display

### 8. Mi A3

Mi A series is known for camera and pure Android experience and MI A3 is successor of MI A2 and Best Thing in MI A3 is its Operating System Which is pure Android Namely AndroidOne.

MI A3 is Built with Qualcomm Snapdragon 665 octa core Processor and 48 MP Rear(Triple Camera) + 32 MP front camera. Mi A3 is also one of the best mobile under 15000 budget.

#### Features of Mi A3

RAM & Storage : 4 GB + 64 GB & 6 GB + 128 GB

Camera : 48MP + 8MP + 2MP | 32MP Front Camera

Battery : 4000 mAH

Processor : Qualcomm Snapdragon 665 Processor

Display : 6.03 HD Display

### 9. Realme 5

Realme 5 is successor of Realme 3. This phone is packed with latest processor of snapdragon 665 Chipset. This phone comes with 48 MP AI Quad camera. Realme 5 has super massive batterry of 5000 mAh.

#### Features of Realme 5

RAM & Storage : 4 GB RAM | 128 GB ROM |

Camera : 12MP + 8MP + 2MP + 2MP | 13MP Front Camera

Battery : 5000 mAH

Processor : Qualcomm Snapdragon 665 Octa Core 2.0 GHz Processor

Display : 6.5 inch HD+ Display

### 10. Redmi Note 7S

Redmi Note 7S is successor of Redmi Note 7S which was launched after any issue in Redmi Note 7.The features of the phone is same as Redmi Note 7 Pro except Processor. In this phone processor used is Qualcomm Snapdragon 660 AIE Processor

#### Features of Redmi Note 7S

RAM & Storage : 4 GB + 64 GB

Camera : 48MP + 5MP | 13MP Front Camera

Battery : 4000 mAH

Processor : Qualcomm Snapdragon 660 AIE Processor

Display : 6.3 inch FHD+ Display

# Best Phone Under 10000

Finding a best mobile under your budget is big challenge. Your budget is whatever but you want all the things in your phone. So after lot of inspection, concluded that which mobile is best under 10000 you should buy. Here we are listing 10 Mobile and their features and reason why you should buy.

## 1. Redmi Note 8

Redmi Note 8 is product of Xiaomi which is very popular Mobile company in India. If you want buy a mobile under 10000 then Redmi Note 8 is best phone under 10000.

If we talk about its features Redmi Note 8 have Full HD+ 6.3 inch display, 4000 mAH battery and 48 megapixel camera which makes phone a perfect device.

### Features of Redmi Note 8

Ram & Storage : 4 GB + 64 GB & 6 GB + 128 GB

Camera : 48 MP + 5 MP | 13 MP Front Camera

Battery : 4000 mAH

Processor : Qualcomm Snapdragon 660 AIE Processor

Display : 16.0 cm (6.3 inch) FHD+ Display

## 2. Realme 5S

Realme 5s smartphone whose AI quad-camera system (48 MP primary lens, 8 MP ultra-wide-angle lens, 2 MP Super Macro lens, and 2 MP portrait lens) allows you to click beautiful pictures of people, landscapes, and anything that captures your eyes. It also comes with the 16.51 cm (6.5) HD+ Mini-drop display that lets you enjoy immersive visuals. Not to forget, this smartphone’s crystal design will make it stand out from the crowd, wherever you place it.

Realme 5s packed with 5000 mAh batterry. Realme 5s is one of the best mobile phone under 10000.

### Features of Redmi Note 7S

Ram & Storage : 4 GB + 64 GB & 4 GB + 128 GB

Camera : 48MP + 8MP + 2MP | 13MP Front Camera

Battery : 5000 mAH

Processor : Qualcomm Snapdragon 665 Processor

Display : 16.51 cm (6.5 inch) HD+ Display

## 3. Redmi Note 7S

Redmi Note 7s is product of Xiaomi which is very popular Mobile company in India. If you want buy a mobile under 10000 then Redmi Note 7S is best phone under 10000.

If we talk about its features Redmi Note 7S have Full HD+ 6.3 inch display, 4000 mAH battery and 48 megapixel camera which makes phone a perfect device.

### Features of Redmi Note 7S

Ram & Storage : 3 GB + 32 GB & 4 GB + 64 GB

Camera : 48 MP + 5 MP | 13 MP Front Camera

Battery : 4000 mAH

Processor : Qualcomm Snapdragon 660 AIE Processor

Display : 16.0 cm (6.3 inch) FHD+ Display

## 4. Realme 5

Realme is covering mid-range market of  phone and Realme 5 is another best mobile under 10000 with best camera, processor, and ram management

Realme comes with Snapdragon 665 Chip Set and Quad Camera Setup with 12 Mega Pixels Primary Camera and 13 Mega pixel. Photos of Realme 5 is Very Good mobile option under 10000 budget

### Features of Realme 5

RAM & Storage:3 GB + 32 GB & 4 GB + 64 GB & 128 GB

Camera : 12MP + 8MP + 2MP + 2MP | 13MP Front Camera

Battery : 5000 mAh Battery

Processor : Qualcomm Snapdragon 665 2 GHz

Display : 16.51 cm (6.5 inch) HD+ Display

## 5. Motorola One Macro

Motorola Launched Moto Macro One in India in Budget price with Ai quad camera, 4 GB Ram with 64 GB Storage which is best for those who want more storage capacity in budget.

Moto Macro One comes with Mediatek P70 Powered by a 2.0 GHz AI-capable Octa-core Processor and 4 GB of RAM, this phone can handle any task that you throw at it. So, we are listing this mobile in Best mobile under 10000

### Features of Motorola One Macro

RAM & Storage:4 GB + 64 GB & 128 GB

Camera : 13MP + 2MP + 2MP | 8MP Front Camera

Battery : 4000 mAh Battery

Processor : MediaTek Helio P70 Processor

Display : 15.75 cm (6.2 inch) HD+ Display

## 6. Samsung Galaxy M30

Vivo Z1 pro is packed phone with huge battery and powered by the Qualcomm Snapdragon 712 AIE processor. It is first phone with this processor in India under 15000 price. Some feature like amoled display is missing but viewing quality is good and in this budget its a perfect phone.

### Features ofSamsung Galaxy M30

RAM & Storage :3 GB + 32 GB & 4 GB + 64 GB & 6 GB + 128 GB

Camera : 13MP + 5MP + 5MP Triple Rear Camera | 16MP front facing camera

Battery : 5000 mAH

Processor : 1.8 GHz Exynos 7904 octa core processor

Display : 16.21 centimeters (6.4-inch) FHD+

## 7. Nokia 8.1

Nokia 8.1 is successor of Nokia 7.1 with improved processor and better camera setup. Nokia 8.1 have extra 500 mAh battery than Nokia 7.1 and display also improved and with Full HD+ Display. Nokia 8.1 have Qualcomm Snapdragon 710 Processor.

If you want pure android experience and also love Nokia phones than Nokia 8.1 is best phone under 15000 for you.

### Features of Nokia 8.1

RAM & Storage : 4 GB + 64 GB

Camera : 12MP + 5MP | 8MP Front Camera

Battery : 3500 mAH

Processor : Qualcomm Snapdragon 710 Processor

Display : 15.7 cm (6.18 inch) Full HD+ Display

## 8. Realme 3 Pro

Realme 3 pro is one of the best low budget phone it competites phones under 15000. It has Android Pie v9.0 operating system with 2.2GHz Qualcomm Snapdragon 710 AIE octa core processor.

### Features of Realme 3 Pro

RAM & Storage : 4 GB + 64 GB & 6 GB + 128 GB

Camera : 16MP+5MP dual rear camera | 25MP front camera

Battery : 4000 mAH

Processor : Snapdragon 710 AIE octa core processor

Display : 6.3 inch FHD+ IPS Display

## 9. Redmi Note 7 Pro

Xiomi Redmi is very popular mobile phone company in india and Note series has a credit of this popularity. Redmi Note 7 Pro is also one of them. Redmi Note 7 Pro has a great built quality with 48 Megapixel camera gorilla glass protection. Powerful processor of Snapdragon 675 make it fast.

### Features of Redmi Note 7 Pro

RAM & Storage : 4 GB + 64 GB & 6 GB + 64 or 128 GB

Camera : 48MP + 5MP | 13MP Front Camera

Battery : 4000 mAH

Processor : Qualcomm Snapdragon 675 Processor

Display : FHD+ IPS Display

## 10. Mi A3

Mi A series is known for camera and pure Android experience and MI A3 is successor of MI A2 and Best Thing in MI A3 is its Operating System Which is pure Android Namely AndroidOne.

MI A3 is Built with Qualcomm Snapdragon 665 octa core Processor and 48 MP Rear(Triple Camera) + 32 MP front camera. Mi A3 is also one of the best mobile under 15000 budget.

### Features of Mi A3

RAM & Storage : 4 GB + 64 GB & 6 GB + 128 GB

Camera : 48MP + 8MP + 2MP | 32MP Front Camera

Battery : 4000 mAH

Processor : Qualcomm Snapdragon 665 Processor

Display : 6.03 HD Display

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