P1 Flashcards
How does red-shift support the Big Band thoery?
Since we cannot assume that we have a special place in the Universe, this is evidence for a generally expanding universe. It suggests that everything is moving away from everything else.
What is all the evidence we have for the big bang theory?
The light from other galaxies is red-shifted soThe other galaxies are moving away from us.
The further away a galaxy is, the more its light is red-shifted. The most likely explanation is that the whole universe is expanding. This supports the theory that the start of the universe could have been from a single explosion.
The Cosmic Microwave Background Radiation, CMBR, exists. The relatively uniform background radiation is the remains of energy created just after the Big Bang.
What is the big bang theory?
The theory states that originally all the matter in the universe was concentrated into a single incredibly tiny point. This began to enlarge rapidly in a hot explosion (called the Big Bang), and it is still expanding today.
Why does the patterns of lines in the adsorption spectrum for helium move towards the red end of the spectrum when the object is further away?
The positions of the lines have changed because of the Doppler effect. Their wavelengths have increased (and their frequencies have decreased).
How does red-shift work and what does it show?
Astronomers have found that the further from us a star is, the more its light is red-shifted. This is because their wavelengths have increased and their frequencies have decreased. If it was moving closer it would be blue. This tells us that distant galaxies are moving away from us, and that the further away a galaxy is, the faster it’s moving away.
How do we know that the sun contains helium?
We know this because there are black lines in the spectrum of the light from the Sun where helium has absorbed light. These lines form the absorption spectrum for helium.
What is the Doppler effect and how does it work?
This effect, where there is a change in frequency and wavelength, is called the Doppler effect.
When a source moves towards an observer, the observed wavelength decreases and the frequency increases giving it a higher pitch.
When a source moves away from an observer, the observed wavelength increases and the frequency decreases giving it a lower pitch.
What has been found that supports the big bang theory?
Astronomers have even detected a cosmic microwave background radiation, CMBR, that is thought to be the heat left over from the original explosion.
What happens when waves meet a medium?
The wave speed slows and its wavelength decreases as it passes through the medium. As it reenters the air, the wave speed and wavelength increase back to their original values.
What are the uses of gamma radiation?
killing cancer cells
How do you calculate wave speed?
v = f × λ
v is the wave speed in metres per second, m/s
f is the frequency in hertz, Hz
λ (lambda) is the wavelength in metres, m.
What are waves?
Waves are vibrations that transfer energy from place to place without matter (solid, liquid or gas) being transferred.
What are transverse waves?
In transverse waves, the oscillations (vibrations) are at right angles to the direction of travel and energy transfer
How can radio waves reach receivers that aren’t in view of the transmitter?
Diffraction allows low-frequency radio waves to be received behind hills, although repeater stations are often used to improve the quality of the signals. The lowest frequency radio waves are also reflected from an electrically charged layer of the upper atmosphere, called the ionosphere. This means that they can still reach receivers that are not in the line of sight because of the curvature of the Earth’s surface.
How do you construct a ray diagram?
In a ray diagram, the mirror is drawn a straight line with thick hatchings to show which side has the reflective coating. The light rays are drawn as solid straight lines, each with an arrowhead to show the direction of travel. Light rays that appear to come from behind the mirror are shown as dashed straight lines. Make sure that the incident rays (the solid lines) obey the law of reflection: the angle of incidence equals the angle of reflection. Extend two lines behind the mirror. They cross where the image appears to come from.
How can microwaves be used to communicate with satellites?
Certain microwave radiation wavelengths pass through the Earth’s atmosphere and can be used to transmit information to and from satellites in orbit. Satellite television signals use microwaves.
What is the range of wavelengths in the electromagnetic spectrum?
about 10–15 m to more than 104 m.
What is the incident?
The incoming ray.
What waves need to travel through a medium?
Sound waves and seismic waves
What is the angle of reflection?
The angle of reflection is between the reflected ray and the normal.
What is the law of reflection?
the angle of incidence equals the angle of reflection
What do smooth surfaces do when light hits them?
Smooth surfaces produce strong echoes when sound waves hit them, and they can act as mirrors when light waves hit them. The waves are reflected uniformly and light can form images The waves can:
appear to come from a point behind the mirror, for example a looking glass
be focused to a point, for example sunlight reflected off a concave telescope mirror.
What does the extent of spreading in diffraction depend on?
The extent of the spreading depends on how the width of the gap compares to the wavelength of the waves. Significant diffraction only happens when the wavelength is of the same order of magnitude as the gap. For example:
a gap similar to the wavelength causes a lot of spreading with no sharp shadow, eg sound through a doorway
a gap much larger than the wavelength causes little spreading and a sharp shadow, eg light through a doorway.
What do rough surfaces do when light hits them?
Rough surfaces scatter sound and light in all directions. However, each tiny bit of the surface still follows the rule that the angle of incidence equals the angle of reflection.
What happens if the waves cross the boundary of 90 degrees?
Refraction doesn’t happen if the waves cross the boundary at an angle of 90° (called the normal) - in that case they carry straight on.
What is the image in a plane mirror?
virtual (it cannot be touched or projected onto a screen)
upright (if you stand in front of a mirror, you look the right way up)
laterally inverted (if you stand in front of a mirror, your left side seems to be on the right in the reflection).
What is the order of the electromagnetic spectrum from high frequency and short wavelengths, to low frequency and long wavelengths?
Granny's Xbox Uses Volts In My Room Gamma radiation X-Rays Ultraviolet Visible light Infrared Microwaves Radio Waves
What is the wavelength?
The wavelength of a wave is the distance between a point on one wave and the same point on the next wave.
What are the uses of infrared?
optical fibre communication, High intensity infrared is used in heaters, toasters and grills, security lights
burglar alarms. Infrared radiation is also used to transmit information from place to place, including:
Remote controls for television sets and DVD players
data links between computers.
What are the uses of radio-waves?
Radio waves are used to transmit television and radio programmes. Television uses higher frequencies than radio.
What are the disadvantages of microwaves?
Some people think that mobile phones, which transmit and receive microwaves, may be a health risk. This is not accepted by everyone, as the intensity of the microwaves is too low to damage tissues by heating, and microwaves are not ionising.
What is the normal?
The normal is a line drawn at right angles to the reflector (medium)
What are longitude waves?
In longitudinal waves, the oscillations are along the same direction as the direction of travel and energy transfer. Longitudinal waves show area of compression and rarefaction.
What does visible light require?
The use of visible light needs the transmitter and receiver to be in the line of sight. But it is more secure against eavesdroppers than radio waves.
What is the amplitude?
As waves travel, they set up patterns of disturbance. The amplitude of a wave is its maximum disturbance from its undisturbed position. Take care: the amplitude is not the distance between the top and bottom of a wave.
What is diffraction?
When waves meet a gap in a barrier, they carry on through the gap. However, the waves spread out to some extent into the area beyond the gap. This is called diffraction.
What are sound waves?
Sound waves are longitudinal waves. Their vibrations occur in the same direction as the direction of travel. Sound waves can only travel through a solid, liquid or gas.
What are Sounds with frequencies above about 20 kHz called?
Ultrasounds
What affects sound and pitch?
the greater the amplitude, the louder the sound
the greater the frequency, the higher the pitch.
What are the uses of microwaves?
cooking, mobile phones
What is the medium?
Some waves must travel through a substance. The substance is known as the medium and it can be solid, liquid or gas.
What is the frequency and what is its unit?
The frequency of a wave is the number of waves produced by a source each second. It is also the number of waves that pass a certain point each second. The unit of frequency is the hertz (Hz). It is common for kilohertz (kHz), megahertz (MHz) and gigahertz (GHz) to be used when waves have very high frequencies.
What is the electromagnetic spectrum?
The electromagnetic spectrum is a continuous range of wavelengths.
How can white light be split?
White light can be split up using a prism to form a spectrum. The light waves are refracted as they enter and leave the prism. The shorter the wavelength of the light, the more it is refracted. As a result, red light is refracted the least and violet light is refracted the most, causing the coloured light to spread out to form a spectrum.
What are X-rays used for?
To produce medical images of bones
What happens if a light ray hits a medium at an angle?
It’s speed and direction changes. As the ray enters the medium it is bent towards the normal. The angel of refraction is less than the angle of incidence. When it leaves the medium the ray is bent back into its original direction.
What is refraction?
Sound waves and light waves change speed when they pass across the boundary between two substances with different densities, such as air and glass. This causes them to change direction and this effect is called refraction.
What are the uses of ultraviolet?
detecting forged bank notes
What is the angle of incidence?
The angle of incidence is between the incident (incoming) ray and the normal
How can we detect infrared radiation?
We cannot see infrared radiation, but we can feel it as heat energy.
What waves don’t need to travel through a medium?
Other waves do not need to travel through a substance. They may be able to travel through a medium, but they do not have to. Visible light, infrared rays, microwaves and other types of electromagnetic radiation are like this.
How is energy produced in stations the use fossil fuels?
A fuel (such as coal) is used to heat up water into steam, which then turns the turbine which powers the generator which produces electricity.
How does wave energy work?
The water in the sea rises and falls because of waves on the surface. Wave machines use the kinetic energy in this movement to drive electricity generators.
What are the two main nuclear fuels?
The main nuclear fuels are uranium and plutonium. These are radioactive metals.
