LIGHT
Reflection of light
- Bouncing back of light after striking a surface is called reflection of light.
Law of reflection
- The incident ray, the normal ray and the reflected ray all lie on same plane of incidence.
- The angle of incidence is always equal to the angle of reflection.
These are of two types
1. Concave Mirror: Image formed by concave mirror is generally real and inverted.
2. Convex Mirror. Image formed by convex mirror is generally virtual, erect and diminished.
Vertex A: The point where principal axis meets the mirror surface point.
Focal Point F: Mid way between vertex and center of curvature.
Radius of curvature R: distance between vertex and center of curvature.
Focal length f: distance from vertex and focal point.
i.e. focal length is half of radius of curvature.
Case 1: When object is at infinity.
Property of image: Image Position at F, Point size, Highly diminished, Real and inverted.
Case 2: When object is placed beyond C, center of curvature.
Property of Image: Position - between F and C, Image size - small, Nature - real and inverted.
Case 3: When object is placed at C.
Property of Image: Position - at C, Image size - same as object, Nature - real and inverted.
Case 4: When object placed between C and F.
Property of Image: Position - behind C, Image size: enlarged, Nature - real and inverted.
Case 5: Object at F, focal length
- Light is a transverse wave, and an electromagnetic radiation with in certain portion of electromagnetic spectrum.
- Speed of light is (3 lac km per second) 3.00×108 m/s or 3.00×106 km/s.
- Sun takes 8 min 19 sec (499 or ~500 sec).
- Reflected light from Moon takes 1.28 ~ 1.3 sec to reach the Earth.
Reflection of light
- Bouncing back of light after striking a surface is called reflection of light.
Law of reflection
- The incident ray, the normal ray and the reflected ray all lie on same plane of incidence.
- The angle of incidence is always equal to the angle of reflection.
Plane Mirror
- Image formed by plane mirror are Virtual (आभासी), Erect (सीधी), Laterally inverted (opposite to original i.e. L to R change to R to L), at the same distance from mirror as the object is and is of same size.
- To see the full image of the observer the minimum height of the mirror should be half the height of the observer.
- If the plane mirror is rotated by an angle θ the reflected ray gets rotated by an angle 2θ.
- Focal length of plane mirror is infinite and power is Zero.
These are of two types
1. Concave Mirror: Image formed by concave mirror is generally real and inverted.
2. Convex Mirror. Image formed by convex mirror is generally virtual, erect and diminished.
Concave Mirror
Principal Axis: Line passing through centre of sphere and attaching to mirror at centre of mirror.
Center of curvature C: The point in center of sphere from which the mirror was sliced.Vertex A: The point where principal axis meets the mirror surface point.
Focal Point F: Mid way between vertex and center of curvature.
Radius of curvature R: distance between vertex and center of curvature.
Focal length f: distance from vertex and focal point.
i.e. focal length is half of radius of curvature.
Case 1: When object is at infinity.
Case 2: When object is placed beyond C, center of curvature.
Property of Image: Position - between F and C, Image size - small, Nature - real and inverted.
Case 3: When object is placed at C.
Property of Image: Position - at C, Image size - same as object, Nature - real and inverted.
Case 4: When object placed between C and F.
Property of Image: Position - behind C, Image size: enlarged, Nature - real and inverted.
Case 5: Object at F, focal length
Property of Image: Position - at infinity, Image size: Highly enlarged, Nature - real and inverted.
Case 6: Object is placed between F and P.
Property of Image: Position - Behind mirror, Image size: enlarged, Nature - virtual and erect.
Convex Mirror
Case 1: When object is at infinity.
Property of Image: Position - Behind mirror at F, Image size: Highly diminished, Nature - Virtual and erect.
Case 2: Object is between Pole and infinity.
Property of Image: Position - Behind the mirror between P & F, Image size: Diminished, Nature - Virtual and erect.
Use of Concave mirror:
- Converging mirror.
- In reflecting telescope.
- Shaving mirror.
- In torch light.
- Headlights.
- Solar oven, solar furnaces.
- By dentists.
- In electron microscope.
Use of Convex mirror.
- Diverging mirror.
- Side view mirror.
- Used in turning of the road or parking.
- Magnifying glass.
- Making lens of sunglasses.
- Street light reflector.
- In supermarket as Anti theft mirror.