light (chapter 13)

Question 1

what are light rays?

Answer 1

straight lines with arrows indicate the direction of light travels.

Question 2

what are bundles of light?

Answer 2

bundle of many light ray forms a light beam.

Question 3

what is the first law of reflection?

Answer 3

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

Question 4

what is the second law of reflection?

Answer 4

the angle of incidence is equal to angle of reflection.

Question 5

what are the types of reflection?

Answer 5

regular reflection and diffuse reflection
(smooth surface). (rough surfaces)
rays are parallel rays are not parallel

Question 6

what are the characteristics of mirror images formed by plane mirrors?

Answer 6

1. mirror images and objects are equally far from the mirror
2. mirror image is virtual
3. mirror image and object are of same size
4. mirror image is laterally inverted
5. mirror image is upright

Question 7

what are the applications of reflections? (teleprompter)

Answer 7

teleprompter’s two-way mirror is both transmitting and reflecting. it allows light from a presenter to reach the recording device. it also reflects words from news script at the same time. the presenter is able to read the news on two-way mirror and maintain eye contact with video camera.

Question 8

what are the applications of reflections (car side mirror)

Answer 8

1. A car’s side mirrors help driver to check for approaching cars from behind before switching. it is also useful when reversing car.

Question 9

what is refraction?

Answer 9

the bending of light as it passes from one optical medium to another

Question 10

when does light bend towards the normal?

Answer 10

i>r
light travels slower in glass
air -> glass

Question 11

when does light bend away from normal?

Answer 11

i<r> air</r>

Question 12

what is the first law of refraction?

Answer 12

first law of refraction states that incident rays, refracted rays and normal at the point of incidence all lie in the same plane.

Question 13

what is the second law of refraction?

Answer 13

second law of refraction states that for two given media, the ratio of the sine at the angle of incidence to the sine of angle of refraction is a constant, that is sin i / sin r = constant

Question 14

what is the refractive index?

Answer 14

the refractive index, n , of a medium is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium.

Question 15

what is the principle of reversibility of rays?

Answer 15

the principle of reversibility of rays states that regardless of how many times a light ray has been reflected or refracted, it will follow the same path when its direction is reversed.

Question 16

what is an emergent ray?

Answer 16

ray that emerges from glass block is known as emergent ray.

Question 17

the effect of refraction (bend objects)

Answer 17

the light rays travelling from water to air refract away from normal. however, our brain tends to tell us that light travels in a straight line. Hence, the light emerging from the water surface appear to diverge from point above the (object). Thus, observer sees the image of (object) at shallower depth.

Question 18

what are converging lens?

Answer 18

a device is made of glass or other transparent materials that is able to concentrate light rays is called converging lens.

Question 19

terms used to describe thin converging lens

Answer 19

principle axis: the line that is passed through the centre of the lens and perpendicular to the plane of the lens.

optical centre C: The point on the principal axis that is midway between the surface of the lens.

principal focal points F: the point on the perpendicular where all rays parallel to the principal axis meet after assign through the lens.

focal plane: the plane perpendicular to the principal axis on which all parallel rays meet after passing through the lens.

focal length f: distance between optical centre C and the principal focal point F.

Question 20

what is the type of image, image distance, uses when the object distance= infinity?

Answer 20

characteristic of image: inverted, real, diminished
image distance: v=f
-image will be on the opposite side of lens
uses: object lens of a telescope

Question 21

what is the type of image, image distance and the uses when the object distance is u>2f

Answer 21

type of image: inverted, real, diminished
image distance: f<v<2f
- image is opposite side of lens
uses: camera, eyes

Question 22

what is the type of image, image distance and the uses when the object distance is u=2f?

Answer 22

type of image: inverted, real, same size
image distance: v=2f
-image will be on opposite side of lens
uses: photocopier making same sized copy

Question 23

what is the type of image, image distance and the uses when the object distance is f<u<2f?

Answer 23

type of image: inverted, real, magnified
image distance: v>2f
-image opposite side of the lens
uses: projector, photograph enlargement

Question 24

what is the type of image, image distance and the uses when the object distance is u=f?

Answer 24

type of image: upright, virtual, magnified
image distance: NIL
-same side of lens
uses: produce a parallel beam of light

Question 25

what is the type of image, image distance and the uses when the object distance is u<f?

Answer 25

type of image: upright, virtual, magnified
image distance: -
-image same side of lens
uses: magnifying glass

Question 26

what are some applications of converging lenses? (visual correction for long-sightedness)

Answer 26

visual correction for long sightedness.
People who are long-sighted, their eyes focus the light rays from each object point to a point beyond the retina.
As light rays are not focused on the retina, the rays from a single object point forms an extended patch instead of a sharply focused point on the retina.
Wearing a pair of spectacles with suitable converging lens, the image focal points can be brought onto retina to form a sharp image.

Question 27

what are the applications of converging lens? (forming image in a camera)

Answer 27

A converging lens is used to form an inverted, real and dismissed image on the sensor of a film camera.
Focusing ring adjusts the lens to sensor distance. At the minimum lens to sensor distance, faraway objects form sharp images on sensor.
As the lens is move further out, nearer objects become more focused.

Question 28

what is a real image?

Answer 28

it is an image formed by converging of light rays at each image point.

Question 29

what is the difference between real image and virtual image?

Answer 29

a real image can be formed on screen but a virtual image cannot be formed on a screen placed at its image plane.