M7 Topic 1 Part 2: Electromagnetic Spectrum - Spectra

Question 1

what are the types of spectra (2)

Answer 1

continuous

Non-continuous

Question 2

what types of non continuous spectra are there

Answer 2

emission

absorption

Question 3

what does a continuous spectra look like

Answer 3

a continuous band of colours (red-violet)

Question 4

when are continuous spectra observed

Answer 4

incandescent objects (ie galaxies)

Question 5

what does a emission spectra look like

Answer 5

a black background with coloured bands

Question 6

how are emission spectra created

Answer 6

When electrons from gases are excited and de-excite releasing energy in the form of electromagnetic waves

Question 7

What does a absorption spectra look like

Answer 7

coloured background with black bands

Question 8

how are absorption spectra created(2)

Answer 8

• when continuous spectra(white light) moves through cooler layers of gas, specific frequencies absorbed
• when a continuous spectra(white light) is reflected off objects specific frequencies are absorbed

Question 9

what are discharge tubes

Answer 9

tubes containing a low-pressure gas through which a current is passed through.

Question 10

how does a discharge tube work in steps (3)

Answer 10

1. the electrical energy excites electrons in the atoms of gas to a higher energy shell/level
2. the excited electrons fall back to a lower energy shell/level releasing energy in the form of EM waves in order to get to it’s ground state
3. Dependant on the amount of energy released by the electron as it moves to a ground state

Question 11

how does a flame test work in steps (4)

Answer 11

1. the salts introduced to the flame atomise
2. the heat energy is absorbed by the electrons going to a higher energy level
3. the energy level lowers releasing energy as it moves to lower energy shells in the form of EM waves which if in the visible spectrum will appear as colours
4. return to ground state

Question 12

what is spectroscopy

Answer 12

when a spectrometer is used to observe emission and absorption spectra

Question 13

how does the spectrometer work

Answer 13

light goes through the prism in the spectroscope revealing the components of the light, which will display a emission or absorption spectra

Question 14

Why can observing emission and absorption spectra identify the components of a star

Answer 14

Each element (gas) has unique emission and absorption lines, which can be compared to that of a star, to identify elements of the star.

Question 15

how is abundance of specific elements observed in a stars emission and absorption spectra

Answer 15

the specific elements line will be more defined if in high abundance

Question 16

how is surface temperature observed

Answer 16

through identifying a blackbody radiation curves peak wavelength

Question 17

how is peak wavelength calculated

Answer 17

wien’s law: 入ₘₐₓ = b/T

Question 18

what does each symbol mean in wien’s law and what unit are they measured in (3)

Answer 18

入ₘₐₓ= peak wavelength of the emitted radiation (metres (m))
b= Wien's constant (2.898 x10⁻³ m K)
T= the surface temperature of the object (Kelvin (K))

Question 19

what are the spectral types from hottest to coldest and what are there colours (7)

Answer 19

O = blue
B = blue-white
A = white
F = yellow-white
G = yellow
K = orange
M = red

Question 20

how can translational velocity to an observer be seen in emission and absorption spectra (2)

Answer 20

The doppler effect- will cause a element’s (gas) emission and absorption spectra to shift:

• To the red side of the spectra (red shift) when moving away from and observer
• To shift to blue side of the spectra (blue shift) when moving closer to an observer

Question 21

what is the equation for the doppler effect

Answer 21

Δ入/入₀=v/c

Question 22

what does each symbol mean in the doppler effect equation and what unit are they measured in (4)

Answer 22

Δ入= wavelength shift (metres (m))
入₀= wavelength of source not moving (metres (m))
v= velocity of shifted source (m/s)
c= speed of light (3x10⁸ m/s)

Question 23

how is rotational velocity of stars observed through emission and absorption spectra

Answer 23

the broadening of absorption and emission lines (defined), the bigger the faster the rotational velocity

Question 24

why do absorption and emission lines broaden when a star has rotational velocity

Answer 24

the side moving closer to the observer blue shifts, whilst the side moving away redshifts thus making the emission and absorption lines appear broader

Question 25

how is density observed through emission and absorption spectra

Answer 25

the broadening of absorption and emission lines (undefined), the bigger the more dense

Question 26

why do absorption and emission lines broaden when stars are more dense

Answer 26

due to the small distance between particles leading to a higher rate of atomic collisions