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GCSE Physics > Lenses and light > Flashcards

Lenses and light Flashcards

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1
Q

What happens when light strikes a reflective surface?

A

It reflects.

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2
Q

Where is the normal line constructed?

A

Perpendicular to the reflecting surface at the point of incidence.

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3
Q

For reflected light, if given the angle of incidence, what will be the angle of reflection?

A

angle of incidence = angle of reflection.

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4
Q

What happens when light crosses an interface?

A

It refracts.

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5
Q

How does a light ray refract when it enters the interface at 90^o along the normal?

A

No refraction occurs.

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6
Q

What is the refractive index?

A

A feature of specific materials related to how the light rays would refract when they enter a medium. It is the ability of a material to bend the ray of light.

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7
Q

What is the equation that can be used to determine the refractive index?

A

(refractive index) = (sin i) / (sin r)

sin i and sin r are the sine values of the angles of incidence and refraction.

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8
Q

What is the refractive index of air?

A

1.0

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9
Q

What is the refractive index of water?

A

1.33

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10
Q

What is the refractive index of glass?

A

1.5

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11
Q

In what direction does light refract?

A

less dense -> more dense; light bends towards the normal

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12
Q

What is a lens?

A

A specially shaped piece of transparent material that refracts light.

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13
Q

What are the two main types of lenses?

A
  1. Converging or convex lens.

2. Diverging or concave lens.

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14
Q

What is a converging or convex lens?

A

A lens that is thickest at the centre and represented by in ray diagrams.

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15
Q

What is a diverging or concave lens?

A

A lens that is thinnest at the centre and represented by >—< in ray diagrams.

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16
Q

What determines the curvature of a lens?

A

The shape of the lens.

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17
Q

What is the curvature of a lens?

A

How much light ray is refracted through a lens.

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18
Q

What happens to a light ray that enters a lens at its centre?

A

It is undeviated. It is called the principal axis of the lens.

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19
Q

What happens to light from an object in a convex lens?

A

It is refracted inwards at the two curved surfaces of the lens so that they meet at the focus.

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20
Q

Where is the image formed in a convex lens?

A

On the opposite side of the lens and is real.

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21
Q

Where is the image formed in a concave lens?

A

On the same side of the lens and is virtual.

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22
Q

What is the focal length?

A

The distance between the centre of the lens and the focus.

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23
Q

What does the size of an image produced by a lens depend on?

A

The distance of the object from the lens.

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24
Q

What kind of image is produced by a convex lens?

A
  1. Real.
  2. Inverted.
  3. Smaller for distant objects and magnified when the object is between F and 2F.

When the object is between the F and the centre of the lens, the image is:

  1. Virtual
  2. Upright
  3. Magnified
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25
Q

What kind of image is produced by a concave lens?

A
  1. Virtual.
  2. Upright.
  3. Smaller.
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26
Q

What equation can be used to calculate the magnification of a lens?

A

(magnification) = (image height) / (object height)

27
Q

What units are used for the magnification of a lens?

A

There are no unts.

28
Q

What kind of lens can be used as a magnifying glass?

A

A converging lens.

29
Q

What is the focal length of a lens determined by?

A
  1. The refractive index of the material from which the lens is made.
  2. The curvature of the two surfaces of the lens.
30
Q

For a given focal length, the greater the refractive index, the what the lens?

A

The thinner the lens.

31
Q

What is the name given to the phenomenon when light enters a converging or diverging lens to form an image?

A

Refraction.

32
Q

If the image height is 4.2 cm and the object height only 0.7 cm, calculate the magnification of the lens.

A

6.

33
Q

How is an image interpreted by the eye?

A
  1. The eye receives light.
  2. It sends this information to the brain via the optic nerve
  3. The brain then interprets the image.
34
Q

What are the 8 main components of the eye?

A
  1. Iris.
  2. Lens.
  3. Pupil.
  4. Cornea.
  5. Ciliary muscles.
  6. Suspensory ligaments.
  7. Optic nerve.
  8. Retina.
35
Q

What is the function of the cornea?

A

To refract most of the light.

36
Q

What is the function of the pupil?

A

To adjust the light intensity.

37
Q

What is the function of the lens?

A

To provide further refraction before the image is formed.

38
Q

Where is the image received by the eye formed?

A

On the retina.

39
Q

What is the function of the optic nerve?

A

To carry information to the brain.

40
Q

What is the function of the ciliary muscles?

A

To control the shape of the eye lens, allowing light from objects at different distances to be brought into focus.

41
Q

Between what distances can the eye focus on objects?

A

Between the near point (approximately 25 cm) and the far point (infinity).

42
Q

What are the two type of defective vision?

A

Long sight and short sight.

43
Q

What is long sight?

A

It is caused by the eyeball being too short and unable to focus on near objects.

44
Q

What is short sight?

A

It is caused by the eyeball being too long and unable to focus on distant objects.

45
Q

How can long sight and short sight be corrected?

A

Using glasses, which adjust the light before entering the eye to allow it to focus correctly. Glasses are made from concave lenses, convex lenses or a combination of both.

46
Q

What kind of lens is used in a camera and magnifying glass?

A

A fixed converging lens with definite focal lengths.

47
Q

What does a magnifying glass do to an object?

A

It enlarges an object size if the distance from the object to the lens is less than the focal length.

48
Q

What kind of image is produced by a magnifying glass?

A
  1. Virtual.
  2. Upright.
  3. Enlarged.
49
Q

Where is the image produced in a camera?

A

On film or via a CCD.

50
Q

What equation can be used to determine the power of a lens?

A

P = 1 / f
P is the power in dioptres, D
f is the focal length in metres, m

51
Q

Is the power of a converging lens positive or negative?

A

Positive.

52
Q

Is the power of a diverging lens positive or negative?

A

Negative.

53
Q

What happens when the angle of refraction is equal to 90^o?

A

The light ray travels on the boundary between glass and air. The angle of incidence is then called the critical angle, c.

54
Q

What equation can be used to determine the refractive index using the critical angle?

A

(refractive index) = (1) / (sin c)

sin c is the sine of the critical angle.

55
Q

What happens when the angle of incidence is greater than the critical angle?

A

Total internal reflection takes place. No refraction occurs so no light escapes from the glass.

56
Q

How do medical endoscopes work?

A
  1. They use the principle of total internal reflection to see inside the body.
  2. Visible light is sent down thin, flexible glass rods called optical fibres, which are inserted into the body.
  3. The image is returned along the same fibres to an eye-piece or camera.
57
Q

What is a laser?

A

A device that amplifies light to produce a very intense and very narrow beam. They can be made from solids, liquids or gases. Modern devices are very small and compact.

58
Q

How are lasers used in eye surgery?

A
  1. To repair damaged retinas.

2. To remove diseased or damaged cells by cutting, cauterising or burning the tissue.

59
Q

What are used to guide laser beams in the body?

A

Optical fibres.

60
Q

What action do the ciliary muscles have within the eye?

A

They control the shape of the lens.

61
Q

What is the normal range of vision of the human eye?

A

25 cm to infinity.

62
Q

What is meant by ‘critical angle’?

A

The angle of refraction is directed along the boundary or at 90^o to the normal.

63
Q

Total internal reflection is used in optical fibres. What is total internal reflection?

A

When a ray of light remains within a material by repeated reflection.

64
Q

Give an example of where total internal reflection has been applied.

A

In medical endoscopes.

GCSE Physics (4 decks)

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