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Light Flashcards

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1
Q

Define reflection.

A

Reflection is the rebounding of light from the surface of an object.

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2
Q

Define diffuse reflection

A

Incident beam of parallel light is reflected in all directions.

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3
Q

Define regular reflection.

A

Incident beam of parallel light is reflected as a beam of parallel light

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4
Q

State the two laws of reflection.

A

Law 1: the incident ray, the reflected ray and the normal all lie in the same plane.
Law 2: the angle of incidence = the angle of reflection

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5
Q

What is the pole of a mirror?

A

The pole of the mirror is the centre of the mirror itself.

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6
Q

What is the centre of curvature?

A

Is the centre of the sphere from which the mirror was cut.

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7
Q

What is the focal point and the focal length?

A

The focal point is half way between the pole and the centre of curvature.
The focal length is the distance between the pole and the focal point.

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8
Q

What is the principal axis?

A

The straight line joining the pole, centre of curvature and focal point.

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9
Q

What are the four rules for drawing diagrams for mirrors?

A

Ray travelling parallel reflects through the focal point.
Ray travelling through the focal point reflects parallel.
Ray striking the pole; angle of incidence = angle of reflection.
Ray travelling through centre of curvature reflects back along it’s path.

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10
Q

Where must an object be positioned for a concave mirror to produce a virtual image.

A

Inside the focal length.

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11
Q

Give two practical uses of a concave mirror.

A

-Shaving mirror or a make-up mirror to give enlarged image of person’s face.
-Dentist’s mirror to give enlarged image of a tooth.

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12
Q

Give two practical uses of convex mirrors.

A

-Security mirror
-Rear mirror for a car
Both give large fields of vision.

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13
Q

What are the rule for f and v and whether they are positive or negative? Differentiate between mirrors and lenses.

A

Real image - v is positive
Virtual image - v is negative
Concave mirror - f is positive
Convex mirror - f is negative
(Diverging lens) Concave lens - f is negative
(Converging lens) Convex lens - f is positive

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14
Q

Define refraction.

A

Refraction is the bending of light as it passes from one medium to another medium of a different refractive index.

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15
Q

State the laws of refraction.

A

Law 1: The incident ray, the refracted ray and the normal all lie in the same plane.
Law 2(Snell’s Law): The sine of the angle of incidence is proportional to the sine of the angle of refraction.

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16
Q

Give the Snell’s law formula for refractive index.

A

n = sin(i) / sin(r)

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17
Q

Refractive index of air to diamond is 2.4, what is the refractive index of diamond to air.

A

1 / 2.4

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18
Q

Formula for refractive index from air to water.

A

Refractive index from air to water = real depth / apparent depth

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19
Q

Formula for refractive index using speed of light.
Formula for refractive index using wavelength.

A

n = C air / C medium
n = lambda 1 / lambda 2

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20
Q

Formula for refractive index using critical angle.

A

n = 1 / Sin(C)
Where n is from air into glass.

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21
Q

Give two uses of optical fibres.

A

Telecommunications industry.
Endoscope used to examine stomach.

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22
Q

What is the optical centre of a lens?

A

The optical centre is the actual centre of the lens itself.

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23
Q

What is the formula for combined focal length of two converging lenses?
What is the formula for combined focal length of one converging lense and one diverging lense?

A

1/f = 1/f1 + 1/f2
1/f = 1/f1 - 1/f2

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24
Q

What is the formula for combined power for two converging lenses?
What is the formula for combined power of one converging lense and one diverging lense?

A

P = P1 + P2
P = P1 - P2

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25
Q

What is the relationship between power and focal length?

A

focal length = 1 / power

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26
Q

What are the three rules for drawing diagrams for lenses?

A

A ray of light travelling parallel to the principal axis refracts through the focal point on the other side of the lens.
A ray of light travelling through the focal point refracts parallel to the principal axis on the other side of the lens.
A ray striking the optical centre passes through the lens undeviated and out the other side of the lens.

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27
Q

Where must an object be placed using a convex lens to produce a virtual image?

A

Inside the focal length

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28
Q

What is the scientific name for long sightedness? Which lense is used to correct it? Where are near objects in focus for such a person?

A

Hypermetropia. Corrected by converging lens. Near objects focused behind the retina and appear blurry.

29
Q

What is the scientific name for short sightedness? Which lense is used to correct it? Where are far objects in focus for such a person?

A

Myopia. Corrected by diverging lens. Far objects focussed in front of the retina and appear blurry.

30
Q

Explain the following functions of the spectrometer.
1. The slit
2. The collimator
3. The table
4. The telescope.
5. The Vernier Scale.

A
  1. Light enters through the slit. The width of the slit may be adjusted using the width control.
  2. A parallel beam of light leaves collimator. Cannot be rotated.
  3. The circular table is graduated in degrees and can be rotated.
  4. The telescope is focused to pick up light from collimator. There are cross wires in the telescope to enable the exact position of the images to be determined. Can be rotated around table.
  5. The Vernier Scale enables the rotation of the telescope in degrees to be measured very accurately.
31
Q

What is diffraction?

A

Diffraction is the spreading out of a wave into the geometrical shadow when it passes through a gap or around an obstacle.

32
Q

Define diffraction grating.

A

A diffraction grating is a series of transparent gaps which are as wide or very close to the wavelength of light.

33
Q

How do you calculate the value of d, the grating constant?

A

The calculate the value of d, you get the reciprocal of the number of lines per metre for the grating.

34
Q

Give two differences between dispersion of white light in a prism and in a diffraction grating.

A

With the prism red light bends (refracts) least.
With the diffraction grating red light bends (diffracts) most
With the prism there is only the first order spectrum.
With the diffraction grating there can be multiple order spectrums. I.e. n=1, n=2, n=3

35
Q

What is the formula for calculating the distance between images on a screen using pieta?

A

DxTan(pieta) = x

D = distance to screen
x = distance between images

36
Q

Give the formula for calculating wavelength using distance to the screen, distance between slits, distance between the centre of two consecutive bright lines on screen.

A

lambda = dx / D

where d is the distance between the lines

37
Q

Define polarisation.

A

Polarisation of light is the process of confining the vibrations of the light wave to one plane only.

38
Q

Explain how electromagnetic radiation causes the temperature of the Earth to increase according to the greenhouse effect.

A

Some of the radiation from the sun that penetrates through the atmosphere is absorbed by the earth and re-emitted. The wavelength of the re-emitted radiation is longer and cannot pass out through the atmosphere. The radiation keeps the planet Earth warm. The gas CO2 is partially responsible for trapping this radiation. The radiation is reflected by the CO2 causing it to continuously re-heat the earth. Since the levels of CO2 are rising due to the burning of fossil fuels, the temperature of the earth is increasing. I.e. the greenhouse effect.

39
Q

What is the maximum value for pieta in n x lambda = d x sin(pieta)

A

90 degrees

40
Q

What happens when white light is diffracted at the zero order?

A

Constructive interference for all colours used, white light reformed.

41
Q

From what line is the angle of incidence and the angle of reflection always measured?

A

The normal

42
Q

How does the eye bring different objects into focus?

A

Changes the shape of the lense. I.e. the focal length of the lense.

43
Q

How is an approximate value for focal length found?

A

Allow light from a distant source to fall onto the mirror/lens. This light comes from “infinity”. Focus this light to form a sharp image on a screen. The distance from the mirror to the screen is the approximate focal length.

44
Q

What happens when you decrease the number of lines per metre on a diffraction grating from 500 per metre to 300 per metre?

A

The value of d increases so
The images are closer together (pieta decreases)

45
Q

What happens when you increase the number of lines per metre on a diffraction grating from 300 per metre to 500 per metre?

A

The value of d decreases so
The images are further apart (pieta increases)

46
Q

In an experiment to measure the wavelength of monochromatic light how was a narrow beam of light produced?

A

Adjusting the width of the slit in the collimator will give a narrow beam of light.

47
Q

Give two reasons why the telecommunications industry uses optic fibres instead of copper conductors to transmit signals.

A

Cheaper raw material
Fibres do not corrode

48
Q

An optical fibre has an outer less dense layer of glass. What is it’s role?

A

Protects the optical fibre from damage.
As it is less dense provides a lower refractive index needed for total internal reflection.

49
Q

Define dispersion.

A

Dispersion is the breaking up of white light into its different constituent colours.

50
Q

How are infra red and ultra violet light detected?

A

Infra red is detected through it’s heating effect.
Ultra violet is detected by fluorescence.

51
Q

Give one application of stress polarisation.

A

To check a piece of material for defects.
Stress analysis tests on transparent plastics.

52
Q

Name three pairs of complimentary colours of light. I.e. together will form white light.

A

Red with turquoise
Green with magenta
Blue with yellow

53
Q

Define critical angle.

A

The critical angle is the angle of incidence in the more dense medium when the angle of refraction in the less dense medium is 90 degrees.

54
Q

Define Total Internal Reflection.

A

When the angle of incidence in the more dense medium is greater than the critical angle, all the light is trapped in the more dense medium. The light reflects off the boundary surface back into the more dense medium. This is called total internal reflection.

55
Q

Why is an image of the moon formed at the focal length?

A

Image is at infinity with incoming rays parallel.

56
Q

What are conjugate foci?

A

The pair of focal points on the principal axis of any lens where an object is placed at the point, image is formed at a perfectly interchangeable point.

57
Q

What is the unit for power of a lens? Unit for focal length?

A

m-1 ; cm

58
Q

When a diver is underwater… Why does the cornea not act as a lens?
Why do objects appear blurred?
Explain how wearing goggles allows objects to be seen clearly.

A

Light not refracted at the cornea as cornea and water have the same n value.
Internal lens not powerful enough to focus light on retina.
Light refracted on passing from air to cornea which now acts as a lens.

59
Q

Why can a diverging lens not be used in a magnifying glass?

A

diminished image always formed.

60
Q

Why would light escape an optical fibre? How can these two things be prevented?

A

Corrosion from seawater causing damage to cladding and fibre.

If the outer medium is not optically less dense than the fibre than total internal reflection cannot occur.

Add more cladding
Use a cladding with a lower refractive index

61
Q

What happens when sodium source is replaced by (a) red light (b) white light

A

(a) greater angular separation
(b) spectrum on either side of white zero order image

62
Q

Why are radiowaves not observed to diffract in a diffraction grating of 600 lines per metre?

A

Wavelength too big; not approximately equal to size of gaps.

63
Q

List two primary colours of light. What colour of light is produced when these two colours mix?

A

Green and red.
Yellow.

64
Q

Why is light dispersed when passing through a substance?

A

Different colours of light travel at different speeds in glass.

65
Q

What colour does a red book appear when (a) white light (b) green light and (c) red light is shined on it.

A

(a) Red (blue and green absorbed)
(b) Black (green absorbed)
(c) Red

66
Q

Give a real life example of light undergoing dispersion.

A

A rainbow

67
Q

If a light source is placed at the bottom of the lake why is only a small circular area lit up?

A

Total Internal Reflection prevents any other light from escaping.

68
Q

When white light is used on a diffraction grating why is a spectrum formed? And why not at the zero order image?

A

Different colours have different wavelengths and bright images formed at different values of pieta.

Constructive interference occurs for all colours.

Physics (16 decks)

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