Light notes refraction, Study notes of Physics

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CLASS 10 NOTESCLASS 10 NOTES

PRASHANT KIRAD

SCIENCE

Light

REFLECTION

The phenomenon where light rays return to the same medium upon

striking a surface is known as "reflection."

Laws of Reflection:

The First Law of Reflection: The incident ray, the reflected ray, and the normal to the surface at the point of incidence, all lie in the same plane.

The Second Law of Reflection: The angle of incidence is equal to the angle of reflection. In other words, the angle between the incident ray and the normal is equal to the angle between the reflected ray and the normal.

These laws of reflection are applicable to the reflection of light from any smooth surface, not just mirrors.

Properties of Image Formed by a Plane Mirror:

1. An image formed by a plane mirror is virtual and erect.
2. The Image is laterally inverted
3. The image formed is as far behind the mirror as the object is in front of it
4. The Size of the image is Equal to that of the Object (m=1)

● Principal axis: The principal axis of a spherical mirror is a straight line that extends through the mirror's pole and its center of curvature. This axis is perpendicular to the mirror's surface at its pole

● Principal Focus: Parallel rays meet at the principal focus (F) for a concave mirror and seem to diverge from the principal focus (F) for a convex mirror. The distance between the mirror's center and the principal focus is the focal length.

● Aperture: The reflecting surface's diameter in a spherical mirror is called the aperture. When the aperture is much smaller than the radius of curvature, we can use R = 2f as an approximation. Ray Diagrams Rules: (1)A parallel ray will either pass through or appear to converge at the principal focus for a concave mirror and appear to diverge from the principal focus for a convex mirror.

2. A ray directed at the principal focus of a concave mirror or passing through the principal focus of a convex mirror will come out parallel to the principal axis.

3. A ray passing through the center of curvature of a concave mirror or directed toward the center of curvature of a convex mirror will be reflected back along its original path
4. Ray incident obliquely to the principal axis towards the pole of the concave mirror on a convex mirror is Reflected Obliquely.

IMAGE FORMATION BY CONVEX MIRROR:

Con: f=(+ve)

Convex mirrors are used in vehicles’s rear-view mirrors to provide smaller but upright images and a wider field of view, enhancing driver visibility.

Sign-convention:

1. Object on the left, light comes from the left.
2. Start measuring from the mirror's pole.
3. Left is negative, right is positive.
4. Above the principal axis is positive.
5. Below the principal axis is negative.

Important:

● The object distance u, is always negative. ● The image distance v, is positive if the image is formed behind a concave mirror and negative if the image is formed in front of the mirror. ● The image distance v, is always positive for a convex mirror. ● The focal length of a concave mirror is always negative and that of a convex mirror is always positive. ● The height of an object is always positive. ● If the image is erect the height is taken as positive and if the image is inverted, the height is taken as negative.

MIRROR FORMULA:

● The distance of the Object from its pole is called the Object distance (u) ● The distance of the Image from its pole is called the image distance (v) ● The distance of the principal focus from the pole is called the focal length (f)

Magnification (m): Magnification Produced by a spherical mirror gives the relative Extent to which the image of an Object is magnified with respect to the Object's size.

1. 0<m<1: Diminished ( Between 0 and 1)

2. m=1: Same Size

3. m>1: Enlarged

# An object is placed at a distance of 8cm from a convex mirror of a

focal length of 12cm. Find the position of the image.

Refraction through a Rectangular Glass slab:

i = Incident Ray

r = Reflected Ray

e = Emergent Ray

● Angle of incidence = Angle of emergence ( ∠ i)=( ∠ e) ● When a ray of light is incident perpendicularly on a plane glass slab, it passes through undeviated. In this case, the angle of incidence (∠i) is 0°, and therefore, the angle of refraction (∠r) is also 0°.

Refractive Index:

The refractive index measures how light changes direction when it moves from air to another material. It shows how fast or slow light travels and bends in different substances, helping us understand its behavior.

Absolute refractive index:

The absolute refractive index is the refractive index of a substance compared to a vacuum (where the first medium is free space or a vacuum). The refractive index of water is 1.33, which means that light travels about 1.33 times slower in water compared to its speed in air.

Spe Quso:

#

Solo:

#

Solo:

● Principal Axis: An imaginary straight line passing through the two centers of curvature of a lens is called its principal Axis.

● Principal focus: The point where parallel rays meet (convex lens) or appear to diverge from (concave lens). Lenses have two such points.

● Aperture: The aperture of a spherical lens is its effective diameter, representing the size of the circular outline.

● Optical center (O): The optical center of a lens is where light

passes through without bending.

● Focal length: Focal length is the distance between the principal focus and the optical center.

RAY DIAGRAMS: Rul: ● Rays parallel to the principal axis converge at the principal focus after refraction in a convex lens, while they appear to diverge from the principal focus in a concave lens.

● A ray passing through or directed to the focus will emerge parallel to the principal axis.

● A ray directed towards the optical center will emerge without deviation.

Image formation by Convex Lens:

Note: We apply sign conventions similar to those used for spherical

mirrors, with the exception that all measurements are taken from the optical center of the lens.

Magnification - Ratio of the height of the Image and the height of the Object Represented by (m)

hi - height of the image

ho- height of the object

(-Ve) Sign shows that the image is virtual & erect.

(+Ve) Sign shows that the image is real & inverted.

Power of Lens:

The power of a lens is a measure of its ability to converge or diverge light and is defined as the reciprocal of its focal length (F) in meters. It is typically measured in diopters (D) and is calculated using the formula:

f - focal length in meter. SI unit => (D) Dioptre

# TOP 7 QUESTIONS

Q.1) As the velocity of light increases, the refractive index of the medium decreases.

Light enters from air to water having a refractive index of 4/3. Find the speed of light in water. The speed of light in a vacuum is 310^{8} m/s. [CBSE 2012] (2 - Marks)*

Solo:

Q.2) An object is placed at the focus of a convex lens. Draw a ray diagram to locate the

position of the image formed, if any. State its position and nature. [CBSE 2013] (2-Marks)

Solo:

Q.3) What is meant by the power of a lens? Give its SI unit. When two or more lenses are

placed in contact, what will their combined power? [CBSE 2012] (2-Marks)

Solo:

Q.4) Differentiate between reflection and refraction of light.

Solo:

Q.7) (a) A concave mirror produces a three-times enlarged image of an object placed 10

cm in front of it Calculate the focal length of the mirror. (b) Show the formation of the image with the help of a ray diagram when the object is placed 6 cm away from the pole of a convex mirror.

Solo:

# Competency-based Question-Answer:

Q. 1 ) A rear-view mirror is a device that allows the driver to see the traffic on the road

behind him. It usually finds its place at the top of the windscreen inside the cabin. This device is one of the most basic but essential safety devices in the vehicle. It provides assistance to the driver during overtaking, parking in reverse gear, etc. Generally, vehicles also have a pair of mirrors attached to the body from the outside. They are known as 'side mirrors or Outer Rear View Mirrors (ORVM) which serve the same purpose. Almost all modern cars mount their side mirrors on the doors-normally at A-pillar rather than the wings (the portion of the body above the wheel well).

(a) What type of Mirror is required to make ORVM in the vehicles? (b) What type of image is formed by such a mirror? (C) Draw a ray diagram to show the formation of an image by this type of mirror. (d) Why are these types of mirrors used as rear-view mirrors in vehicles?

Solo:

(a) Convex Mirror (b) Convex mirror always forms an erect, virtual, and diminished image for all positions of the object placed in front of it.

(c)

(d) Convex mirrors are used as rear-view mirrors in vehicles to see the traffic at the rear side (or back side) because- (i) a convex mirror always produces an erect image of the object; (ii) the image formed in a convex mirror is highly diminished due to which a convex mirror gives a wide field of view.

Q. 2 ) The above images are those of a specialized slide projector. Slides are small

transparencies mounted in sturdy frames ideally suited to magnification and projection since they have a very high resolution and a high image quality. There is a tray where the slides are to be put into a particular orientation so that the viewers can see the enlarged erect images of the transparent slides. This means that the slides will have to be inserted upside down in the projector tray. To show her students the images of insects that she investigated in the lab, Mrs. Iyer brought a slide projector. Her slide projector produced a 500-times enlarged and inverted image of a slide on a screen 10 m away. (CBSE 22-23 SQPs)

(a) Based on the text and data given in the above paragraph, what kind of lens must the slide projector have?