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Physics Revision Questions – You must learn the answers to each of these questions Question Answer 1 What is the difference between the geocentric and the heliocentric models of the universe? The geocentric model has the earth at the centre of the solar system and everything else orbiting around it. Whereas the heliocentric has the sun at the centre and the planets orbiting around it. 2 Why did Scientists change their opinion on the model of the solar system from the geocentric to the heliocentric? Originally Scientists thought the earth was at the centre of everything but by using telescopes to observe and plot the movements of other planets this was found to be incorrect. 3 Describe how Galileo’s observations of Jupiter provided evidence of the heliocentric model of the solar system. Using a telescope Galileo plotted the movements of Jupiter’s 4 moons around Jupiter thus proving not everything orbits the earth. 4 How do Scientists observe the solar system and the milky way today? Relatively closer luminous objects in the solar system give out visible light that can be observed using telescopes on the earth or in space. Objects further away in the milky way may give out only small amounts of visible light so are better observed using other types of telescopes that pick up radio waves or microwaves. 5 What is a converging lens? 6 How do you measure the focal length of a converging lens using a distant object? A lens that makes light rays from a distant object bend together and focuses them at a point a small distance from the lens. Clamp a lens and focus the image from a distant object onto a fixed screen by moving the lens until a clear image is formed. Measure the distance from the lens to the screen, then repeat the experiment and average the results. 7 What factors affect the magnification of a converging lens? How curved the surface of a lens is and how close together lenses are placed. 8 What is the difference between a real and a virtual image? A real image is when the rays of light are bought together by a lens and the image is observed on a screen, whereas a virtual image is when the image is observed on a surface like a mirror. 9 How does the eyepiece on a simple telescope work? The eyepiece lens is a small converging lens that is used to magnify the image produced by the larger converging lens at the other end of the telescope. 10 How does a reflecting telescope work? A reflecting telescope uses a large curved mirror to focus the rays from a distant object. Once focussed the image is magnified using a converging eyepiece lens. 11 What happens to light as it passes from one material to another? Some of it will be reflected (bounced off) and some will be refracted (bent). 12 What is refraction and what causes it? Refraction is the bending (change of direction) of a wave as it passes between different materials. It is caused by the slowing down or speeding up of the wave. 13 What do waves transfer? Energy and information but not matter 14 Give examples of longitudinal waves (where the direction of the vibration is the same as the direction of energy travel). Sound waves (including ultrasound and infrasound) and seismic P (primary) waves. 15 Give examples of transverse waves (where the direction of the vibration is perpendicular to the direction of energy travel). All of the electromagnetic waves including light etc and seismic S (secondary) waves. 16 What are the standard units for speed? Metres per second (m/s). 17 What are the standard units for distance? Metres (m). 18 What are the standard units for time? Seconds (s). 19 What is the frequency of a wave and what is it measured in? The number of waves in 1 second and the unit is Hertz (Hz) 20 What is the wavelength and what is it measured in? The length of 1 complete wave cycle. It is measured in meters (m). 21 What is the amplitude and what is it measured in? The distance from the centre of a wave to the top of the wave. It is measured in meters (m). 22 As the wavelength of a wave increases, how is its frequency changed? (Assuming that it is travelling at a constant speed). The frequency would decrease. 23 How did Herschel and Ritter discover waves outside the limit of the visible spectrum? Herschel noticed that if you split visible light up and measured the temperatures of the different colours the red light was hottest. He then moved the thermometer just outside the red colour where he could see no light and the thermometer recorded an even higher temperature. He called this wave energy Infrared. Ritter also split visible light up but looked for wave energy at the other end of the spectrum (the other side of the violet light). He tried to detect the presence of wave energy using silver chloride that he knew reacted with violet light faster than red light. He found that an unseen energy at this point in the spectrum made the silver chloride react even quicker. He called this energy Ultraviolet. 24 What are the colours of light in the visible spectrum? (Start with the longest wavelength) Red, Orange, Yellow, Green, Blue, Indigo, Violet. 25 What is the order of waves in the electromagnetic spectrum? (Start with the longest wavelength) Radio waves, Microwaves, Infrared waves, Visible light, Ultraviolet rays, X-rays, Gamma rays. 26 Are the electromagnetic waves transverse or longitudinal Transverse 27 Which travels faster in a vacuum light or radio waves? Neither, all electromagnetic waves travel at the same speed in a vacuum. 28 Which end of the electromagnetic spectrum has waves of the longest wavelength? Radio waves 29 Which end of the electromagnetic spectrum has waves of the highest frequency? Gamma rays 30 What are the harmful effects of excessive exposure to: 1. Microwaves 2. Infrared 3. Ultraviolet 4. X-rays and gamma rays? 31 As the frequency of a wave increases, what happens to the potential danger? 32 Name some of the uses of: 1. Radio waves 2. Microwaves 3. Infrared 4. Visible light 5. Ultraviolet 6. X-rays 7. X-rays 33 Name 3 types of ionising radiation that transfer energy? Alpha particles, beta particles and gamma rays 34 Where does ionising radiation come from? Radioactive sources continuously emit ionising radiation. 35 What is the solar system and what is it part of? It is made up of the sun and the 8 planets that orbit it and it is part of the milky way galaxy. 36 What is a galaxy? A collection of stars. 37 Put the following in order of size starting with the smallest. Sun, universe, moon, planet, galaxy, earth. Moon, Planets (Earth), Sun, Galaxy, Universe. 1. Internal heating of body cells 2. Skin burns 3. Damage to surface cells and eyes, leading to skin cancer and eye conditions 4. Mutation or damage to cells in the body It increases too because of the increased energy. 1. Broadcasting, communications and satellite transmissions. 2. Cooking, communications and satellite transmissions 3. Cooking, thermal imaging, short range communications, optical fibres, TV remote controls and security systems. 4. Vision, photography and illumination. 5. Security marking, fluorescent lamps, detecting forged bank notes, disinfecting water. 6. Observing the internal structure of objects, airport security scanners and medical X-rays. 7. Sterilising food and medical equipment and the detection of cancer and its treatment. Most objects that astronomers observe give out energy in all parts of the electromagnetic spectrum and modern telescopes can detect almost all of it. Xray, ultra violet, radio waves are commonly detected as well as light. 38 What other regions of the electromagnetic spectrum are used by modern telescopes? 39 What methods are used to search for life beyond earth? Space probes orbit other planets like mars photographing the surface so Scientists can decide where water might have been. The scientists can then land Landers to do soil experiments and look for life in the most promising spots. 40 What is SETI? The Search for Extraterrestrial Intelligence, it analyses radio waves from space and look for signals by intelligent beings. So far nothing has been detected. 41 What is a spectrometer? A device that can split up the different wavelengths of light. (It splits light into its different colours). 42 Name a common object that could be used as a spectrometer. A CD or DVD or a prism (a triangular shaped piece of glass). 43 What is the advantage of the Hubble space telescope? As it is situated above the atmosphere so that light from distant objects enters it without being refracted or reflected from out atmosphere which creates clearer images. 44 Describe the life cycle of stars like our Sun Stage 1: Nebula - a cloud of dust and gases (mainly hydrogen) pulled together by gravity. Stage 2: Star (main sequence) - As the nebula grows the gravitational pull gets stronger and the pressure and the heat builds resulting in the formation of a star. Stage 3: Red giant - When most of the hydrogen has fused into helium the core collapses and the outer layers expand. Stage 4: White dwarf - The red dwarf throws off a shell of gas and what remains will be pulled together by gravity and collapses. No further reactions happen inside a white dwarf. 45 How is the evolution of larger stars different? Large stars become red super giants after the main sequence. After the red super giant phase the star will rapidly collapse and then explode (a supernova). If what is left is 4 or more times the mass of our sun gravity pulls the remains together to form a black hole. If the remains are not that big gravity still pulls the remains together to form a neutron star. 46 What is the Big Bang theory? The whole universe started out as a tiny point of concentrated energy about 13.5 billion years ago. Since the big bang the universe has been expanding ever since. 47 What is the Steady State theory? The universe has always existed and has been continuously expanding with new matter being created as it expands. 48 Both theories believe the universe is expanding, why is this? When light from far away stars is split using a spectrometer the light appears to have a longer wavelength than we would expect (it is moved towards the red end of the spectrum). This is called red shift and can be explained if the source that is emitting the light is moving away from us. 49 Why do we hear the Doppler effect when an aircraft flies over us? The aircraft is moving relative to us and so will have higher frequency sound waves in front of it (because the waves are compressed) and lower frequency waves behind (because the waves are stretched). As the aircraft passes us the pitch of the sound will decrease. 50 How do we know that galaxies further way from us are moving faster than galaxies closer to us? 51 Why do most Scientists believe the Big Bang theory is correct? 52 What is Ultrasound? 53 Give uses of ultrasound. 54 What is Infrasound? 55 Give uses of infrasound. 56 57 What causes seismic waves? Why is it difficult to predict earthquakes? The faster a galaxy moves, the more red shift is seen. Observations show us that there is more red shift from more distant galaxies and so they must be moving faster. Microwave radiation can be observed all over the sky, this is called Cosmic Microwave Background (CMB) radiation. Its presence can be explained by the big bang but not the steady state theory. Sound with frequencies greater than 20 000 Hertz (Hz). This is a range of frequencies greater than humans can hear. Sonar, communication between animals, foetal scanning. Sound with frequencies lower than 20 Hertz (Hz). This is a range of frequencies less than humans can hear. Communication between animals, detection of animal movement in remote places, detection of volcanic eruptions and meteors. Earthquakes or explosions. The earth’s tectonic plates are constantly moving and there are never two occasions when the amount of 58 Name 2 types of seismic wave. 59 What causes these seismic waves to reflect and refract? 60 How can the epicentre of an earth quake be found? 61 Why do the earths tectonic plates move? 62 What can P-waves travel through? 63 What can S-waves travel through? 64 What causes an earthquake? 65 What is the difference between current and voltage? 66 What is a renewable and non-renewable energy source. 67 What are the advantages of non-renewable sources of energy? What are the disadvantages of renewable sources of energy? How can a current of electricity be Induced? How can a larger current be induced? 68 69 70 71 What is the difference between direct current (DC) and alternating current (AC)? 72 What does a transformer do and how does it work. energy needed to move the surface is the same. Longitudinal (P) waves and Transverse (S) waves. (Where P = primary and s = secondary). Both waves move through the centre of the earth which is made of different materials. When these waves reach a boundary they can be reflected or refracted. We know that P waves travel faster than S waves. Both are produced at the same time so by measuring the time difference between their arrival at the seismometer, we can work out how far away the epicentre is from the monitoring station. If there are at least 3 monitoring stations the epicentre can then be triangulated. There are convection currents in the earth’s Mantle (Hot liquid rock underneath the earth’s crust) that force liquid rock up between plate boundaries forcing the plates to move apart. P-waves can travel through solid and liquid at speeds of about 10km/s. So these waves can travel from one side of earth through to the opposite point. S-waves can travel through solids but NOT liquids at speeds of about 6km/s. So these waves cannot travel through the liquid outer core of the earth and cannot be detected at the opposite point on the earth. At plate boundaries, tectonic plates slide past one another. Current is the ‘rate of flow of charge’ and voltage is the ‘electrical pressure giving a measure of the energy transferred’. Non-renewable: Once it has been used it has been effectively lost. (examples include coal, oil and gas (fossil fuels) and uranium.) Renewable: It can be used again and again. (examples include: wind, wave, solar, geothermal, hydroelectric, bio fuels etc.) Possible to generate large amounts of electricity reliably and relatively cheaply. Not always reliable, often expensive, don’t generate a lot of electricity in comparison to non-renewables. By moving a magnet by a coil of wire. By moving the magnet or coil faster, by using a bigger coil or a stronger magnet (an electromagnet is cheapest), putting an iron core inside the coil of wire. DC is always in one direction. For example the current from a battery or solar cell. AC changes polarity because it is constantly changing direction. For example in a generator. A transformer changes the voltage of an AC supply. 73 Why is electrical energy transmitted at high voltages? 74 Where would step up and step down transformers be used in the national grid? 75 What unit is electrical energy from the mains measured in? What is power and what units is it measured in? What are the standard units for current? 76 77 78 79 80 81 82 83 What are the standard units for voltage? When calculating the cost of electricity in £ what are the units for a) Power b) Time c) Cost of 1kWh? What are the standard units for energy transferred? What are the hazards of transmitting electricity? Low energy light bulbs cost more to buy than filament lamps. Why are they considered better? 84 85 How do you calculate the payback time for an installation (in £)? Can energy be created? Name 9 different types of energy. 86 What is efficiency? 87 What unit do we usually use with efficiency? To increase the voltage you need less coils of wire on the left of the iron core and more on the right. This is a step up transformer. To reduce the voltage the opposite is true. This is a step down transformer. An alternating current flows into the primary coil. This makes a magnetic field in the core. The magnetic field changes direction 100 times a second. The changing magnetic field induces a current in the secondary coil. The induced current is alternating too. It improves efficiency by reducing heat loss in the transmission lines by allowing a lower current to be used. Step up transformers are used in power stations whereas step down transformers are used before electricity enters factories and again before it enters homes, offices and shops. Kilowatt-hours It is the rate of transferring energy. It is measured in Watts (W). amps (A). Volts (V). a) kilowatts (kW) b) Hours (h) c) Pounds (£) Joules (J) High voltages could cause electrocution. The have a lower power rating and so they use less energy per second. This makes them cheaper to run. These bulbs last much longer and so as well as reducing energy use they also reduce waste which is better for the environment. = Cost of installing (£)/Saving per year (£) No, it can only be transferred. Energy is conserved. Light, thermal (heat), sound, electrical, Kinetic (movement), chemical, gravitational potential, elastic potential, nuclear. A measure of how much of the energy is transferred into a useful energy type. % 88 89 How does a system remain at a constant temperature? What type of surface best absorbs and emits heat energy. It needs to radiate the same average power (measured in Watts (W)) as it absorbs. A matt black surface.