P7 - Further Physics Flashcards
How is the position of stars relative to a fixed point on the equator measured?
Using the angles of declination and right ascension
What directions are right ascension and declination?
Right ascension -> east - west
Declination -> north - south
What are the units of right ascension?
Degrees and minutes (1 hour = 15 degrees)
How long is the moon’s orbit of earth?
28 days
Why can we see the moon at night?
It reflects the sun’s light
In terms of eclipses, what happens during the waxing phases?
The lit area of the moon gets bigger
In terms of eclipses, what happens during the waning phases?
The lit area of the moon gets smaller
Name the 8 phases of the moon in order
HINT start with the new moon
- New moon
- Waxing crescent
- First quarter
- Waxing gibbous
- Full moon
- Waning gibbous
- Last quarter
- Waning crescent
How does a solar eclipse occur?
A solar eclipse occurs when the moon passes between the earth and the sun and casts a shadow on the earth.
How does a lunar eclipse occur?
A lunar eclipse occurs when the earth is between the sun and moon and casts a shadow on the moon.
Why don’t eclipses occur monthly? (2)
- The moon’s orbit is inclined at a 5 degree angle above Earth so its shadow is usually above or below earth also the full moon isn’t always in earth’s shadow
- Eclipses can only occur when the moon passes through the ecliptic
How long is a solar day?
24 hours
What happens to waves when they are refracted?
The frequency remains the same but the wavelength changes and so does the wave speed
What is the formula for wave speed/ velocity?
Velocity = Frequency x Wavelength
What happens to waves when they are diffracted?
They spread out at the edges
When is diffraction most obvious? (2)
- when the size of the gap is similar to or smaller than the wavelength
- when the waves that pass an object have a wavelength larger than the object
Give the other name for convex lenses
Converging lenses
What do convex lenses do?
They refract rays of parallel light towards a focal point
The image made at the focus of a convex lens is… (3)
- Inverted (upside down)
- Smaller than the original image
- A Real image
The … the curvature of a lens the … its power
The greater the curvature the greater its power
The formula to work out the power of a lens is? Include units
Power (Dioptres) = 1 / the focal length (metres)
What are the two lenses used in a refractor telescope and how powerful are they in relation to each other? (3)
Two converging lenses of different power are used, one is the objective lens and the other is the eyepiece lens. The eyepiece lens has the greater of the two.
How do refractor telescopes work? (2)
- the objective lens captures parallel light and brings it to a focal point
- this point is also the focal point of the eyepiece lens so the image acts as the object of that lens and is magnified
How is angular magnification calculated?
Angular magnification = Focal length of objective lens / focal length of eyepiece lens
Name the 6 issues surrounding refractor telescopes:
- The glass objective lens is heavy when scaled up
- The glass can “run” if it becomes too heavy to support its own weight
- Glass lenses are expensive
- The weight of the lens can cause the tube itself to bend
- The image can be of poor quality
- Chromatic aberration
Describe chromatic aberration:
The image becomes blurred because as the colours of light are dispersed by the lens, the focuses of the various colours of light are spread around the focal point
What are the main parts of an astronomical (reflector) telescope? (4)
- aperture
- plane mirror
- concave mirror
- eyepiece lens
Why must the aperture of a reflector telescope be large? (2)
- to reduce the effects of diffraction and be bigger than the wavelength of radiation
- to allow as much light as possible
What are the advantages of using reflector telescopes? (4)
- the use of mirrors means they are cheaper to make
- more lightweight since mirrors are lighter than glass
- mirrors don’t have he same issues as glass and do not “run”
- mirrors are easier than glass to sculpt perfectly
How long is a sidereal day?
23 hours 56 minutes (4 mins less than a solar one)
What is the conversion of astronomical units to kilometres?
1au = 150 million km
How much is a second of arc?
1/3600 of a degree
What is the formula to calculate how far away a star is? include units
Distance to a star (parsecs) = 1 / parallax angle (seconds of arc)
What is the conversion of parsecs to light years?
1 parsec = 3.2 light years
How many parsecs is 1 mega parsec?
1 million parsecs
What is a parsec?
The distance to a star with a parallax angle of one second of arc
What two factors do a star’s luminosity depend on?
Its size and temperature
What two factors does a star’s observed luminosity depend on?
Its luminosity and distance from Earth
What is the equation to work out the period of a Cepheid?
Period = 1 / frequency of pulses
The ____ the period, the _____ the star
The longer the period the brighter the star
Why are Cepheids known as standard candles?
Because we know/ can work out their luminosity
When was the Curtis-Shapley debate?
1920
What did scientists in the 20s call nebulae?
Fuzzy objects in the sky :)
What were Curtis and Shapley’s two main beliefs? (4)
Curtis thought the sun was the centre of the galaxy and that the universe contained many galaxies, he thought the nebulae were galaxies
Shapley thought the sun wasn’t the centre of the Galaxy and that the nebulae were clouds of gas in our Galaxy; he thought that our one Galaxy made up the universe
What did Edwin Hubble do? (3)
- He observed Cepheids and found one nebula that was very far away
- He provided evidence that the nebula was a separate Galaxy by collecting data on Cepheids in other galaxies
- He showed that most nebulae were distant galaxies
How did Hubble’s work help astronomers?
he allowed astronomers to measure distances to other galaxies and therefore determine the scale of the universe
What is the equation for the Hubble constant?
Hubble constant = Speed of recession / Distance
How many parsecs in a mega parsec?
One million
Extrasolar planet
A planet that orbits a star other than the Sun
The amount of pressure a gas has depends on: (2)
- number of collisions per second
* the momentum of the particles
What is the gas law associated with pressure and volume?
Pressure X volume = constant
Increasing the temperature of a gas can increase the: (2)
Volume or the Pressure (with a fixed volume)
What is the gas law related to Pressure and temperature?
Pressure / temperature = constant
What is the gas law related to volume and temperature?
Volume / temperature = constant
What temperature in Degrees Celsius is absolute zero?
-273 degrees Celsius
Why is absolute zero called that?
Because it is the point at which the particles in a chemical have no vibrational energy and stop moving
What is the unit of Absolute temperature and how does it convert to Degrees Celsius
Kelvin or K
0K = -273 degrees Celsius
273K = 0 degrees Celsius
To convert Kelvin to Celsius, -273 and to covert Celsius to Kelvin, add 273
What are the 6 layers of a star: outer to inner
Corona, Photosphere, Chronosphere, Convective zone, radiative zone, core
What happens in the photosphere of a star?
Photons are radiated into space
What happens in the convective zone of a star?
Energy is emitted as photons and transferred to the surface by convective currents
What happens in the radiative zone of a star?
Photons of radiative energy are transferred to the surface
What happens in the core of a star?
Hottest and densest part of the star and the site of nuclear fusion where high energy protons are released
Explain which emission spectra have lines/ gaps: (3)
- Electrons can jump between shells in an atom.
- They gain energy to move to a new she’ll and release photons of one wavelength when they return back
- There are several ways to move in an atom so different wavelengths are made
Describe the steps of star birth: (6)
- Stars begin in nebulae and when a nearby supernova explodes, the star birth commences
- Compression and gravity make the gas on the nebula collapse
- The force of gravity pulls the gas inwards, causing the pressure and temperature to increase
- As more gas is drawn in, the force of gravity increases
- Gravity compresses the star further and it becomes hotter and denser, forming a protostar
- Temperature and pressure gets so high that fusion starts and energy is released so a main sequence star is born
What are the 3 steps/ equations for nuclear fusion in main sequence stars?
- H(1,1) + H(1,1) -> H(2,1) + positron + neutrino
- H(1,1) + H(2,1) -> He(3,2)
- He(3,2) + He(3,2) -> He(4,2) + 2 Neutrons
What is Deuterium?
An isotope of hydrogen formed but nuclear fusion with a mass of 2
What is Einstein’s equation? And what are the units of each
E=mc(squared)
E = energy in joules
M = mass in kg
C = the speed of light in a vacuum in m/s
What are the two paths of the life cycle of a star?
Nebula -> Average star -> Red Giant -> White Dwarf
Nebula -> Massive star -> Red supergiant -> supernova -> black hole OR neutron star
What requirements are needed for an earth based telescope?
- high altitude
- isolated location
- equatorial location
- frequent cloudless skies
What other factors affect the placement of an earth based telescope? (3)
- cost
- environmental and social impact
- employee working conditions
What are the advantages and disadvantages of space based telescopes? (2.2)
ADV: Avoid absorption and refraction of atmosphere; Can use radiation that the atmosphere absorbs
DISADV: Expensive; Space programmes have some uncertainties
What are the advantages of Computer controlled telescopes? (4)
- Can track objects easily. Data can be collected over a long period of time
- Can be controlled easily in hard to reach areas
- Co-ordinates can be accurately entered
- The computer can record and process data
What are the advantages of sharing telescopes: (3)
- Cost of building is shared
- Expertise shared
- Astronomers can book time on telescopes
What are the three ways telescopes can be accessed?
- By remotes controlled computer
- On the Internet
- Directly in person
