Waves Section

Question 1

How can you increase the spacing between the maxima?

Answer 1

• Increase the separation of the sources
• Increase the wavelength of the waves
• Increase the distance between the sources and screen/detector

Question 2

What is the amplitude of a wave?

Answer 2

The distace from the centre of a wave to the crest or trough.

Question 3

What is meant by irradiance?

Answer 3

The power per unit area

Question 4

What are the 4 differences in spectra produced by refraction (in a prism) and by a grating?

Answer 4

Prism Grating

One spectrum Many spectra

Produced by Refraction Produced by interference

Red light deviated least Red light deviated most

Spectrum is dim Spectrum is bright

Question 5

Are all photons produced by energy level transitions visible?

Answer 5

No, some frequencies of photons may be in in the ultraviolet or X-ray frequency

Question 6

What is destructive interference?

Answer 6

Destructive interference occurs when two waves meet at a point exactly 180^O out of phase.

Question 7

What is meant by diffraction?

Answer 7

Diffraction is the bending of waves round an object.

Question 8

What is the ground state?

Answer 8

This is the energy level with the least energy. It is the most negative energy level.

Question 9

What is the test for a wave?

Answer 9

If it can cause interference.

Question 10

What do absorption lines in the Sun’s spectrum show?

Answer 10

Evidence for the composition of the upper atmosphere of the Sun.

Question 11

What is a coherent source?

Answer 11

Waves that have a constant phase difference (and the same frequency, wavelength and velocity)

Question 12

When will total internal reflection occur?

Answer 12

• Incident light must arrive at the boundary at an angle greater than the critical angle
• Occurs when light tries to pass from an optically dense material to a less dense material (e.g. from glass to air)

Question 13

What is the critical angle?

Answer 13

The angle of incidence (within a material) that gives an angle of refraction of ninety degrees.

Question 14

If white light is shone through a grating what does the interference pattern look like?

Answer 14

• The central order maximum will be white
• At every other maxima a spectrum will be produced

Question 15

If a spectral line is bright - what des this tell you?

Answer 15

More electrons are making that energy level transition producing more photons of light with the same frequency.

Question 16

What are the main features of the Bohr model of the atom?

Answer 16

1. Positively charged central nucleus.
2. Electrons (negatively charged) are in discrete energy levels and do not radiate energy
3. When an electron makes a transition from one energy level to another a specific amount of energy is lost or gained
4. Each line in a spectrum is produced when an electron moves from one energy level to another.

Question 17

What is a minima?

Answer 17

A point where destructive interference occurs.

Question 18

How are absorption lines in the Sun produced?

Answer 18

Photons of certain frequencies are absorbed by the gases in the outer atmosphere of the Sun.

Question 19

What are the advantages of using a grating to produce an interference pattern instead of a double slit?

Answer 19

• Fringes are brighter
• Fringes are sharper

Question 20

What is a point source?

Answer 20

This is a source where the light spreads evely in all directions

Question 21

What is the Law of Reflection?

Answer 21

Angle of incidence = Angle of reflection

Question 22

What is the wavelength of a wave?

Answer 22

Wavelength is the distance from a point on one wave to the same point on the next wave.

Question 23

What will increase the amount of diffraction?

Answer 23

• Longer wavelengths diffract more
• Narrower gaps cause more diffraction

Question 24

What is meant by absolute refractive index?

Answer 24

It is the ratio of speed of light in a vacuum to the speed of light in the material.

Question 25

What is the frequency of a wave?

Answer 25

The number of waves per second.

Question 26

Using a grating how can you increase the spacing between the maxima?

Answer 26

• Use a grating with a smaller slit separation.
• Use a source with a greater wavelength of light
• Move the screen further away

Question 27

When is the energy of the ionisation level?

Answer 27

0 Joules

Question 28

What is constructive intereference?

Answer 28

This occurs when two waves meet at a point in phase.

Question 29

What is irradiance?

Answer 29

The power per unit area

Question 30

What is a maxima?

Answer 30

A point where constructive interference occurs.

Question 31

What type of spectrum is this?

Answer 31

Line absorption spectrum

Question 32

What is the ionisation level?

Answer 32

This is the energy needed by an electron to leave the atom altogether.

Question 33

What type of spectrum is this?

Answer 33

Continuous spectrum

Question 34

A triangular prism can be used to split white light into a spectrum. Why does this occur?

Answer 34

Different frequencies/colours have different refractive indices.

Question 35

What is the period of a wave?

Answer 35

The time it takes one wave to pass a point.

Question 36

What is refraction?

Answer 36

The change in speed of light (and wavelength) as it enters a different material, this can result in a change in direction.

Question 37

What type of spectrum is this?

Answer 37

Line emission spectrum