Light

Question 1

What are the laws for the reflection of light?

Answer 1

Angle of incidence equals angle of reflection.

Incident ray, reflected ray and normal all lie in same plane.(can all be drawn on flat sheet of paper).

Question 2

Where is the angle of incidence found?

Answer 2

Angle between incident ray and normal.

Question 3

Where is the angle of reflection found?

Answer 3

Between reflected ray and normal.

Question 4

What are the properties of the image formed by a plane mirror?

Answer 4

1. Image is same size.
2. Image is upright.
3. Image is virtual.
4. Image is laterally inverted.
5. Image is same distance behind mirror as object is in front.

Question 5

What is a real image?

Answer 5

Image that can be projected onto a screen.

Question 6

What is a virtual image?

Answer 6

Image that cannot be projected onto a screen.

Question 7

What happens when light passes from one medium to another?

Answer 7

The light refracts (it bends).

Question 8

What is refraction?

Answer 8

Change in direction a light ray undergoes when it enters a medium with a different refraction index.

Question 9

What happens to the speed of light as it travels in materials of different refraction indexes?

Answer 9

It changes speed.

Question 10

What speed does light travel in a vacuum?

Answer 10

299,792,458ms.

Question 11

What are the requirements for refraction to take place?

Answer 11

1. Ray passes from one medium into another with different refraction index.
2. At an angle of incidence >0 degrees.

Question 12

What are everyday examples of refraction?

Answer 12

Glasses, fibre optic cables, telescopes, magnifying glasses, binoculars and endoscopes.

Question 13

What is another thing that happens to light as it passes from one medium to another, such as air to glass?

Answer 13

Part of the light is reflected back into first medium (4%) and rest passes into second medium with direction changed (96%).

Question 14

What changes in the light when it enters glass from air?

Answer 14

Speed decreases
Lambda decreases
Frequency remains constant

Question 15

What changes in the light when it exits glass into air?

Answer 15

Speed increases
Lambda increases
Frequency remains constant

Question 16

What direction does light deviate when passing from air to glass?

Answer 16

Towards the normal.

Question 17

What direction does light deviate by when passing from glass to air?

Answer 17

Away from the normal.

Question 18

What is a situation when light passes from air to glass but does not deviate?

Answer 18

Angle of incidence is 0.

Question 19

What does the amount of refraction depend on?

Answer 19

Change of speed of light.

Question 20

What does white light consist of?

Answer 20

Continuous range of different colours.

Question 21

How do we know that white light contains a continuous range of different colours?

Answer 21

Rainbow.

Question 22

What happens when white light passes through droplets of water?

Answer 22

Different colours of light are refracted by different amounts.

Question 23

Why do the colours separate when light passes through droplets of water or a glass prism?

Answer 23

Each colour travels at different speeds.

Question 24

What happens to red light as it is refracted from white light?

Answer 24

Slows down least and so is refracted least.

Question 25

What happens to violet light as it refracts from white light?

Answer 25

Slows down most and so is refracted most.

Question 26

What are the colours of light contained in white light?

Answer 26

Red, orange, yellow, green, blue, indigo, violet

Question 27

What similarity do all colours of light share?

Answer 27

All travel at same speed in air.

Question 28

What happens to all colours of light when leaving a prism?

Answer 28

All refract away from normal as they speed up.

Question 29

What happens when the angle of incidence is smaller than the critical angle in internal reflection?

Answer 29

Refraction takes place. Small amount of light, 4%, is internally reflected.

Question 30

What happens when the angle of incidence is equal to the critical angle in internal reflection?

Answer 30

Angle of refraction is 90 degrees. Partially reflected ray.

Question 31

What happens when the angel of incidence is greater than the critical angle in internal reflection?

Answer 31

Total internal reflection takes place.

Question 32

What is the definition of the critical angle?

Answer 32

Critical angle is the (limiting) angle of incidence which gives an angle of refraction of 90 degrees.

Question 33

What are the 2 conditions necessary for total internal reflection to take place?

Answer 33

1. Angle of incidence > critical angle. 2. Ray must be incident from a higher refractive index medium to a lower refractive index medium.

Question 34

What two requirements does an optical fibre satisfy?

Answer 34

1. Core has very high refractive index while cladding has lower refractive index. 2. As long as i > C, TIR takes place.

Question 35

What does an optical fibre allow you to do?

Answer 35

Transfer of large quantities of data along cable at very large speeds over long distances.

Question 36

What is an endoscope?

Answer 36

Instrument that allows images from inside a persons body to be seen by a physician.

Question 37

What do endoscopes use fibre optic cables for?

Answer 37

1. To deliver non-coherent light into body. 2. To take coherent light from body back to eyepiece to form a clear image.

Question 38

What is the terminology required for CCEA exams when describing how optic fibres going from the body/ object to eye or computer need to be coherent?

Answer 38

Same Spatial Relationship.

Question 39

What are some non medical applications of optic fibre?

Answer 39

1. Bomb disposal. 2. FBI - surveillance. 3. Boroscope - engineers use to inspect aircraft engines, gas turbines, steam turbines, Diesel engines etc.

Question 40

What is a lens?

Answer 40

A carefully ground or moulded piece of transparent material which refracts light rays in such a way to form an image.

Question 41

What are the 2 forms of lens?

Answer 41

Converging - thickest at centre Diverging - thinnest at centre

Question 42

What are the characteristics of converging lenses?

Answer 42

Thicker across middle. Thinner at its ends. Serves to converge light.

Question 43

What are the characteristics of diverging lenses?

Answer 43

Thinner across middle. Thicker at its ends. Serves as to diverge light.

Question 44

What can lenses be thought of as?

Answer 44

Series of tiny refracting lenses.

Question 45

How do a series of tiny refracting lenses form an image?

Answer 45

Each refracts light to produce own image. When prisms act together, they produce bright enough image focused at a point.

Question 46

What other names can a converging lens be referred to as?

Answer 46

Biconvex Convex

Question 47

What other names can a diverging lens be referred to as?

Answer 47

Biconcave Concave

Question 48

What happens to the rays on a converging lens?

Answer 48

All rays travel parallel to principle axis, converge, and pass through focal point of lens.

Question 49

What happens to the rays on a diverging lens?

Answer 49

All rays travelling parallel to principle axis, appear to diverge from focal point in diverging lens.

Question 50

What is the focal length of a converging lens?

Answer 50

Distance from optical centre of lens to focal point.

Question 51

What is the distant object method?

Answer 51

Method used to get estimate of focal length of converging lens.

Question 52

What is the method of the distant object method?

Answer 52

When light travels sufficiently far away from object, rays of light assumed to be parallel. Distance can be taken approx 10m or more. When parallel rays of light pass through converging lens they all pass through focal point. If screen is placed at focal point a sharp image will be detected on screen. Distance from screen to centre of lens (optical centre) is approx focal length of lens.

Question 53

When can the focal length be found?

Answer 53

When image is sharpest.

Question 54

What are the properties of the image formed for a diverging lens?

Answer 54

Diminished (smaller) Upright/erect Virtual

Question 55

What are the properties of the image formed for a converging lens when the object is beyond 2F?

Answer 55

Inverted Diminished (smaller) Real

Question 56

When is an example of a converging lens where the object is beyond 2F?

Answer 56

Eyes or camera

Question 57

What are the properties of the image formed for a converging lens when the object is at 2F?

Answer 57

Inverted Same size Real

Question 58

What are the properties of the image formed for a converging lens when the object is between 2F and F?

Answer 58

Enlarged/magnified Inverted (upside down) Real

Question 59

What is an example for a converging lens where the object is between 2F and F?

Answer 59

A projector

Question 60

What happens in a converging lens when the object is at F?

Answer 60

Image is formed at infinity (never formed).

Question 61

What are the properties of the image formed for a converging lens when the object is between F and the optical centre?

Answer 61

Upright/erect Virtual Magnified/enlarged

Question 62

What is an example of a converging lens where the object is between F and the optical centre?

Answer 62

Magnifying glass.

Question 63

What is the far point?

Answer 63

Farthest point away that human eye can see unaided.

Question 64

What is the distance of the far point for the normal human eye?

Answer 64

Infinity

Question 65

What is the near point?

Answer 65

Nearest point ways that unaided human eye can see.

Question 66

What js the distance of the near point for the normal human eye?

Answer 66

0.25m

Question 67

What is short sight?

Answer 67

When people can see things that are close, but far away things are blurred.

Question 68

What is the distance of the far point for a person who is short sighted?

Answer 68

Much closer than infinity.

Question 69

What is the distance of the near point for a person who is short sighted?

Answer 69

Closer than 0.25m.

Question 70

What is short sight also known as?

Answer 70

Myopia

Question 71

What is the problem caused by short sight?

Answer 71

Images formed of objects beyond person’s far point formed in front of retina. Why they look blurry and lack clarity.

Question 72

What are 2 things that cause short sight to happen?

Answer 72

1. Lens is too powerful. 2. Eye is too long.

Question 73

How is short sight corrected?

Answer 73

Use diverging lens in glasses.

Question 74

What is long sight?

Answer 74

When person can see things clearly that are far away, but close things are blurred.

Question 75

What is the distance of the far point for a person who is long sighted?

Answer 75

Infinity

Question 76

What is the distance of the near point for a person who is long sighted?

Answer 76

Farther away than 0.25m.

Question 77

What is the problem caused by long sight?

Answer 77

Images formed of objects inside person’s near point focused behind retina. Hence look blurry and lack clarity.

Question 78

What are 2 things that cause long sight to happen?

Answer 78

1. Lens too weak. 2. Eye is too short.

Question 79

What can long sight be corrected?

Answer 79

Using converging lens in glasses.

Question 80

What is the function of the eye?

Answer 80

Receives, refracts light to produce image which is interpreted and signals are to brain.

Question 81

How does light form an image in the eye?

Answer 81

Light rays must be focused on small area of retina in back of eye.

Question 82

What parts of the eye focuses light rays entering the eye?

Answer 82

Cornea and lens.

Question 83

What is accommodation in the eye?

Answer 83

Cornea partly reflects light rays which go through lens which Finley adjusts focusing. Lens does this by changing its thickness.

Question 84

Wha this the difference between the bending of light (refraction) for focusing on nearby objects compared to far away objects?

Answer 84

Ore bending refraction needed for focusing on nearby objects.