P5.3 - Wave Interaction

Question 1

What is reflection?

Answer 1

Reflection is when a wave reverses direction upon meeting the boundary between two media.

Question 2

What do all wave phenomena occur at?

Answer 2

All wave phenomena only occur at the boundary between two different media.

Question 3

What is a medium?

Answer 3

A medium is a substance/material of the same particles.

Question 4

What boundary does reflection occur at?

Answer 4

Reflection occurs at the air-glass boundary.

Question 5

What is a ray diagram?

Answer 5

A ray diagram explains how and where mirrors (and lenses using refraction) form images of objects.

Question 6

What is the normal line in ray diagrams?

Answer 6

The normal line intersects the mirror/lens boundary at exactly 90 degrees.

The normal line meets perpendicular to the boundary.

Question 7

What is the incident ray?

Answer 7

The incident ray is a ray of light that comes towards the mirror/lens, the boundary.

Question 8

What is the reflected ray?

Answer 8

The reflected ray is a ray of light that moves away from the mirror/lens having interacted with the boundary.

Question 9

What is the angle of incidence?

Answer 9

The angle of incidence is the angle the incident ray makes with a normal.

Question 10

What is the angle of reflection?

Answer 10

The angle of reflection is the angle the reflected ray makes with the normal.

Question 11

What is a plane mirror?

Answer 11

A mirror which is perfectly flat and reflects back all the light incident upon it.

Question 12

What is the law of reflection?

Answer 12

• The angle of incidence, i = The angle of reflection, r.

- Only true for plane mirrors.

Question 13

What is refraction?

Answer 13

• Refraction is the change in direction of a wave when
  its speed changes as a result of going from one
  medium to another.

Question 14

What happens as a wave crosses a boundary between two media?

Answer 14

• Refraction.
• As a wave crosses the boundary between two
  different media, part of its wavefront changes speed
  first. This results in the wave changing speed. Hence,
  the direction of the wave changes and it is observed
  to bend.

Question 15

What do convex lenses do?

Answer 15

• Converge light rays.
• Make parallel rays passing converge
  (focus) to a point.
• Used in magnifying lenses, cameras forming an image
  of an object, correcting long sight.

Question 16

What do concave lenses do?

Answer 16

• Diverge light rays.
• Make parallel rays passing through it diverge
  (spread out).
• Used for correcting short sightedness.

Question 17

What is the principal focus for lenses.

Answer 17

• The point where lights parallel rays meet or appear to
  meet.
• On both sides of the lens.

Question 18

What is the focal length?

Answer 18

• The distance from the lens to the principal focus.
• Same focal length on each sides of the lens.
• The shorter the focal length the more powerful the
  lens because it has refracted light rays more.

Question 19

What happens in normal vision?

Answer 19

In normal vision, the eyes’ lenses focus rays of light onto the retina of the eye.

Question 20

How do rays from nearby and distant objects travel?

Answer 20

• Rays from nearby objects appear to travel diverging to
  each other.
• Rays from distant objects appear to travel parallel to
  each other.

Question 21

Describe how short sightedness occurs and what type of lens fixes it?

Answer 21

• Eye lens is too powerful (refracts light rays a lot).
• Eyes can only focus light rays from objects nearby as
  the light rays enter the eyes diverging.
• Eyes cannot focus light rays from objects far away
  onto the retina, instead focussing rays in front of retina
  as light rays enter eyes travelling parallel.
• A concave lens is used to diverge parallel light rays
  before they enter the eyes.

Question 22

Describe how long sightedness occurs and what type of lens fixes it.

Answer 22

• Eye lens is weak (refracts light rays a little).
• Eyes can only focus light rays from objects far away as
  the light rays enter the eyes parallel.
• Eyes cannot focus light rays from objects nearby
  onto the retina, instead focussing rays ‘behind’ the
  retina as light rays enter eyes travelling diverging.
• A convex lens is used to converge diverging light rays
  before they enter the eyes.

Question 23

What is a real image?

Answer 23

A real image is an image that is formed where light rays meet.

Question 24

What is a virtual image?

Answer 24

A virtual image is an image that is formed where light rays appear to come from.

Question 25

What is an upright image?

Answer 25

An image which is the same way as the object.

Question 26

What is an inverted image?

Answer 26

An image which is upside down compared to an object.

Question 27

How do you calculate magnification on a ray diagram?

Answer 27

Magnification = Image height / Object height

Question 28

What magnification indication image magnification and image diminishing.

Answer 28

- Magnification > 1 IMAGE MAGNIFIED | - Magnification < 1 IMAGE DIMINISHED

Question 29

What image is produced when an object is placed outside the focal point/principal focus of a convex lens?

Answer 29

- Same type of image formed which happens in eye. - Real. - Inverted. - Diminished.

Question 30

What image is produced when an object is placed inside the focal point/principal focus of a convex lens?

Answer 30

- Same type of image formed in a magnifying glass. - Virtual. - Upright. - Magnified.

Question 31

What image is produced when an object is placed out the focal point/principal focus of a concave lens?

Answer 31

- Virtual. - Diminished. - Upright.

Question 32

What do thicker lenses (given the same material have)? | Explain.

Answer 32

- Thicker lenses have shorter focal lengths. - Light spends more time travelling through a thicker lens, so will end up being bent more. - Shorter focal length means light converges more for convex lenses and diverges more for concave lenses.

Question 33

What is dispersion?

Answer 33

Dispersion is the splitting of white light into its constituent wavelengths (spectrum).

Question 34

Why does dispersion happen?

Answer 34

- Different wavelengths of EM radiation travel at different speeds within glass, so refract by different amounts. - The smaller the wavelength/the higher the frequency, the more the refraction.

Question 35

What does it mean if an object appears only a certain colour in white light?

Answer 35

- If an object appears a certain colour under white light, for example blue. - It is reflecting only that frequency (blue) and absorbing all the other frequencies.

Question 36

What does reflection from surfaces depend on?

Answer 36

- Reflection from surfaces depends on the type of material. - Specular reflection produces sharp images, for example a mirror. - Diffuse scattering produces no images, for example a sheet of paper.

Question 37

Why does milk appear white when ink appears black?

Answer 37

- Light can be scattered from particles. - Milk appears white because its particles scatter all wavelengths. - Ink appears black because its particles absorb all wavelengths.

Question 38

Why does the sky appear blue?

Answer 38

The molecules in the atmosphere are very small and scatter light with short wavelengths such as blue, which is why the sky appears blue.

Question 39

What do filters do?

Answer 39

- Filters absorb certain frequencies of light but | transmit others.

Question 40

Give an example of how a red filter works?

Answer 40

A red filter absorbs all the different frequencies of white light except the small band of frequencies that we call red.

Question 41

Why does no light look get through a red and green filter put a few cm apart from each other?

Answer 41

- The red filter only transmits red light which the green filter absorbs. - The green filter cannot transmit red light and hence no light gets transmitted. - The no light 'looks' black

Question 42

Explain why some clouds appear white, but some appear dark?

Answer 42

- White clouds scatter all/most wavelengths of light. | - Dark clouds absorb most wavelengths of light.

Question 43

Why is a yellow fish black when a blue light is shone onto it?

Answer 43

The fish can absorb all the frequencies of light except the yellow which is reflects. However, the blue light does not contain the frequency for the yellow light to be reflected and hence the fish appears black.

Question 44

Explain how a blue balloon can be both blue and black?

Answer 44

- Blue balloons reflect blue wavelengths of light, under white light. - Red light contains only red light wavelengths. - This, when illuminated by red light, the blue balloon will absorb the red light and reflect nothing, appearing black. appearing black.

Question 45

Suggest why you do not see a spectrum when white light goes through a rectangular glass block.

Answer 45

- A rectangular block has two lines of symmetry. - Thus, the final refracted beam travels parallel to the original incident beam. - Therefore, the different wavelengths of light within the white light, aren't separated out.