459693
Description
Flashcards by Anna Hollywood, updated more than 1 year ago
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Created by Anna Hollywood
almost 11 years ago
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| Question | Answer |
| When are the forces of gravity only noticeable? | On an astronomical scale |
| Why do planets stay in orbit around the sun? | Because of gravitational attraction |
| What is the force applied to the centre of an orbit? | The centripetal force |
| The larger the mass the greater/weaker the gravitational force? | Greater |
| The further away an object is the smaller/greater the gravitational force | Smaller |
| Force is indirectly proportional to... | 1 ------------- distance squared |
| Why is the orbit time for a planet closer to the sun less? | Shorter distance...faster (greater gravity) |
| How does a satellite orbit the earth? | At a tangent and gravity makes it accelerate towards the earth |
| Whereabouts do polar satellites orbit? | 20-100km above the north and south poles |
| How long do polar satellites take to orbit the earth? | About 90 minutes |
| How much of the earth's can polar satellites see? | All of it |
| What are polar satellites used for? | Imaging the earth-including short range weather forecasting |
| Whereabouts do geostationary satellites orbit? | Above the equator |
| How long do geostationary satellites Take to orbit? | 24 hours |
| What are geostationary satellites used for? | Communication |
| How do you calculate the distance travelled by a satellite? | 2 x (pi) x radius (from centre of earth) |
| All geostationary satellites must be in different/the same orbit | The same |
| Why can't geostationary satellites be too close together? | As their signals would overlap due to diffraction |
| What is a scalar quantity? | Only magnitude (e.g. speed) |
| What is a vector quantity? | Magnitude and direction (e.g. velocity) |
| What are vectors normally represented by? | Arrows |
| What is 3m/s to the right + 2m/s to the left? | 1m/s to the right |
| How is the resultant of two forces that are not in the same direction found? | By using Pythagoras (to find size) and trigonometry to find the angle |
| What does U stand for in equations of motion? | Initial velocity |
| What does V stand for in equations of motion? | Final velocity |
| What does A stand for in equations of motion? | Acceleration |
| What does S stand for in equations of motion? | Distance travelled |
| What does T stand for in equations of motion? | Time taken |
| What is the acceleration of an object thrown into the air? | -10m/s(squared) |
| What is the velocity of a ball at the top of its ascent? | 0 |
| A ball thrown horizontally from the top of a tower will fall at the same rate as a ball dropped from the top of a tower. True or false? | True |
| What is the trajectory of a ball thrown horizontally? | Parabolic/A parabola |
| What equation do we use to work out the horizontal motion of a ball? | distance = speed x time |
| What type of horizontal velocity does a ball have (been thrown from tower)? | Constant |
| What is the resultant velocity? | The vector sum of the constant horizontal velocity and the vertical velocity |
| What do forces always occur in? | Pairs |
| The action and reaction pairs of forces are... (3 things) | equal in size...opposite in direction...act on different objects |
| What law is it that states that forces come in pairs? | Newton's third law |
| Why do we have weight? | Because we are attracted to Earth due to gravity |
| What is the opposite force to us being attracted to Earth? | Earth being attracted to us |
| Why does a gun recoil after a bullet is shot out of it? | Because the bullet exerts the same amount of force onto the gun than the gun does to the bullet |
| What is the opposite of an explosion? What is still conserved? | A collision. Momentum |
| How does pressure build up in a gas container? | The particles of the gas collide with the walls of the container, creating a force (and hence a pressure) on the walls |
| How does a larger volume increase pressure? | Particles collide with walls of container more often, more energy, more pressure |
| How does increasing the temperature increase pressure? | Particles move faster...hit walls more often...with greater force...increasing pressure |
| Force = rate of change of (what?) | momentum |
| As a rocket moves up, the hot gases released move ......... . Momentum is ................ . This means that the high momentum of the large massed rocket moving up is ............... by the high velocity of the exhaust gases. | As a rocket moves up, the hot gases released move DOWN. Momentum is CONSERVED. This means that the high momentum of the large massed rocket moving up is BALANCED by the high velocity of the exhaust gases. |
| What are microwaves sent into space by? | A parabolic transmitter |
| What satellites are used to receive, amplify and re-transmit the microwaves back to earth? | Geostationary satellites |
| When microwaves return to earth, what are they received by? | Parabolic receiver |
| Why are digital signals used for satellite communication? | They do not attenuate as quickly and there is less noise |
| What frequencies of radio waves does the ionosphere reflect? | Below 30 MHz |
| What happens when radio waves with frequencies above 30 MHz meet the ionosphere? | They get absorbed and scattered, reducing signal strength |
| What range of frequencies are used for satellite communication? | Between 3GHz and 30GHZ |
| How high above the earth do geostationary satellites orbit? | 36,000km |
| Why is the size of a geostationary satellite's dish many times bigger than the microwaves wavelength? | So their is very little diffraction and this produces a narrow beam that doesn't spread out |
| Why do the receiving dish and transmitting dish need exact alignment? | To ensure the signal hits the geostationary satellite |
| What do microwaves do as they are fired into space? | Pass through the Earth's atmosphere and (as they have a very small wavelength) don't spread out much |
| What is the ionosphere? | A region between 100km and 500km above the Earth |
| What do radio waves undergo as they enter space? | A series of refractions and they speed up as they go, eventually undergoing total internal reflection |
| The smaller the size of a gap the greater/lesser the diffraction | Greater |
| Which of these diffracts more.... radio waves or TV signals? | Radio waves (TV signals transmitter and receiver MUST be in line of sight) |
| When does maximum diffraction occur? | When the wavelength is equal to the size of the gap |
| Why would radio waves diffract in a hilly area? | As they have long wavelengths compared to the distance between hills |
| What will happen if you place two speakers (connected to the same output) and place them about 1 metre apart? | You will hear alternate loud and quiet areas as you move along a line in front of them |
| What does it mean when two crests/troughs overlap? | The waves are in step and the sound will be loud |
| What does it mean when a trough and a crest overlap? | The waves are out of step and the sound will be quiet |
| What is constructive interference? | The waves meet in phase |
| What is destructive interference? | Waves meet out of phase |
| Show the diagram for constructive interference | |
| Show the diagram for destructive interference | |
| In terms of half wavelengths, when does constructive interference occur? | When there are an equal number of half wavelengths |
| In terms of half wavelengths, when does destructive interference occur? | When thee are an odd number of half wavelengths |
| Generally, when does interference between light waves occur? | When light diffracts as it passes through narrow slits |
| What kind of interference is light bands and what kind of interference is dark bands? | Light - constructive Dark - destructive |
| Why do the slits have to be closer together than the speakers? | Because light wavelengths are shorter than sound wavelengths |
| What kind of waves are electromagnetic waves? | Transverse waves |
| When is light polarised? | If the oscillations are only in one direction at right angles to the wave direction |
| How do polaroid sunglasses work? | They stop oscillations in all but one direction at right angles to the wave, reducing the amount of light that passes through |
| What did Newton think of light as and why was he wrong? | As a particle and if this was true then light would travel faster in a denser medium |
| What did Huygens think of light as? | A wave |
| Why does refraction occur? | Because when light enters a different medium, it changes speed |
| What does light do as it enters a more dense medium and why? | It slows down - it deviates towards the normal |
| What does light do as it enters a less dense medium and why? | It speeds up - it deviates away from the normal |
| What is the refractive index? | A number that is the ratio of the two speeds of the speed of light between air and a medium |
| What is the equation for working the refractive index? | RI (n) = speed of light in vacuum ---------------------------- speed of light in medium |
| Why does dispersion occur? | Because each colour slows down by a different amount when white light enters a medium and speeds up by different amount when leaving |
| What does Snell's law state? | RI (n) = sin incidence --------------- sin refraction |
| When light passes from a more dense medium into a less dense medium the angle of refraction is ................ than the angle of incidence | Larger |
| What is the critical angle? | The angle of incidence in the more dense medium that produces an angle of refraction of 90 degrees in the less dense medium |
| What happens if the critical angle is exceeded? | The light is totally internally reflected |
| What do optical fibres rely on? | Total internal reflection |
| What three things are optical fibres used for? | -Carrying telephone conversations -Carrying computer data -For endoscopes |
| The higher the refractive index of a material, the higher/lower its critical angle | Lower |
| n = 1 ---- ? | sin c |
| A parallel beam of light from a distant object can be .................... to a focus in the ........... plane | converged, focal |
| What happens if the beam is parallel to the principal axis? | The light is focused to the focal point on the principal axis |
| What will a diverging beam from a near object do? | It will focus at a point beyond the focal plane |
| How does a camera work? | Light passes through lens...focused on film...size of image is smaller than object |
| How is a projector different to a camera? | Same thing happens but the film is closer to lens and so image is bigger than object |
| What can we do to find the position and size of an image created by a convex lens? | Use a scale diagram |
| What happens to the top ray? | Refracted through focal point of convex lens |
| What happens to lower ray? | No deviation, goes straight through |
| What are the two properties of an image formed by a magnifying glass? | Right way up and cannot be projected onto a screen |
| What is the difference between simple and more advanced cameras? | More advanced have sharper images at any distance as they have an adjustable lens |
| What is the aperture? | An adjustable hole allowing different amounts of light onto the film |
| What do the condenser lenses do in a projector? | Make sure the film is uniformly illuminated |
| What does the curved mirror do in a projector? | Reflects light back into the condenser lenses |
| Magnification = | image size --------------- object size |
| Why can't the image produced by a magnifying glass be projected onto a screen? | It is virtual - no light passes through it |
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