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23:[["$","$L32",null,{"feature":"flashcards"}],"$L33",["$","$L34",null,{"href":"/gcse/physics/ocr/beyond-earth/flashcards","label":"Beyond Earth","subjectCode":"gcse_physics__ocr","surface":"flashcards"}],["$","$L35",null,{"runner":["$","div",null,{"className":"min-h-0 flex-1 overflow-hidden bg-background","children":["$","$L36",null,{"decks":[{"id":"a866351e-cf27-47c7-969a-dbd5a6ef0696","title":"Beyond Earth Flashcards","topicId":"e6a05d67-2c0b-5412-a7d1-78b35957f51c","topicSlug":"beyond-earth","cards":[{"id":"9ee36476-4b5e-4fef-afce-f664ca8e0703","cardType":"basic","points":1,"front":"What force holds objects in orbit around the Sun?","back":"Gravity.","mcqOptions":[{"text":"Gravity.","correct":true,"explanation":"Gravity attracts orbiting objects towards the Sun, providing the inward centripetal force needed to keep them moving along curved orbital paths."},{"text":"Electromagnetic force.","correct":false,"explanation":"Electromagnetic forces act between charged particles, but they do not maintain planetary orbits. Gravity provides the attractive force holding objects in orbit around the Sun."},{"text":"Nuclear force.","correct":false,"explanation":"The nuclear force binds particles within atomic nuclei and acts only over extremely short distances. Gravity holds planets and other objects in solar orbit."},{"text":"Friction.","correct":false,"explanation":"Friction opposes motion between contacting surfaces and is negligible in space. The Sun’s gravitational attraction supplies the centripetal force required for an orbit."}]},{"id":"3d41aa25-9a1c-4090-b6af-4c1ed54c8605","cardType":"cloze","points":null,"front":"The Sun emits electromagnetic radiation because of [ ] in its [ ].","back":"The Sun emits electromagnetic radiation because of nuclear fusion in its core.","mcqOptions":[{"text":"The Sun emits electromagnetic radiation because of nuclear fusion in its core.","correct":true,"explanation":"Nuclear fusion in the Sun’s core combines hydrogen nuclei and releases energy. This energy eventually leaves the Sun as electromagnetic radiation."},{"text":"The Sun emits electromagnetic radiation because of nuclear fission in its core.","correct":false,"explanation":"Nuclear fission splits heavy nuclei and is not the Sun’s energy source. The Sun releases energy through nuclear fusion occurring in its core."},{"text":"The Sun emits electromagnetic radiation because of nuclear fusion in its photosphere.","correct":false,"explanation":"The photosphere is the visible surface from which much radiation escapes, but fusion does not occur there. Nuclear fusion takes place in the Sun’s core."},{"text":"The Sun emits electromagnetic radiation because of chemical combustion in its core.","correct":false,"explanation":"Chemical combustion cannot produce the Sun’s enormous energy output or sustain it for billions of years. Nuclear fusion in the core is the source."}]},{"id":"b7e17089-b7c2-46a1-98b4-387eaaaf43b9","cardType":"cloze","points":null,"front":"A natural satellite forms [ ]; an artificial satellite is [ ].","back":"A natural satellite forms naturally; an artificial satellite is human-made.","mcqOptions":[{"text":"A natural satellite forms naturally; an artificial satellite is human-made.","correct":true,"explanation":"Natural satellites arise through natural astronomical processes, whereas artificial satellites are constructed and launched by humans for purposes such as communication or observation."},{"text":"A natural satellite forms artificially; an artificial satellite is human-made.","correct":false,"explanation":"Calling a natural satellite artificial reverses its defining feature. Natural satellites form naturally, while artificial satellites are made and launched by humans."},{"text":"A natural satellite forms naturally; an artificial satellite is naturally occurring.","correct":false,"explanation":"Artificial satellites do not form through natural astronomical processes. A natural satellite forms naturally, while an artificial satellite is deliberately human-made."},{"text":"A natural satellite forms human-made; an artificial satellite is naturally occurring.","correct":false,"explanation":"This reverses the two definitions. Natural satellites form naturally, whereas artificial satellites are human-made objects placed into orbit."}]},{"id":"d72fa016-6ab0-4b53-a1b6-0e20b07e295a","cardType":"basic","points":1,"front":"Which satellite orbit stays above the same point on Earth and is useful for communications?","back":"Geostationary orbit.","mcqOptions":[{"text":"Geostationary orbit.","correct":true,"explanation":"A geostationary satellite orbits above the equator once every 24 hours in Earth’s rotational direction, so it remains above the same location."},{"text":"Polar orbit.","correct":false,"explanation":"A polar satellite passes over or near both poles and moves above different locations as Earth rotates. A geostationary orbit remains above one point."},{"text":"Low Earth orbit.","correct":false,"explanation":"Low Earth orbit describes an altitude range rather than an orbit fixed above one location. Communications satellites that remain stationary use geostationary orbit."},{"text":"Elliptical orbit.","correct":false,"explanation":"In an elliptical orbit, a satellite’s distance and speed vary, so it does not remain above the same point. Geostationary orbit provides fixed coverage."}]},{"id":"2c5a70c9-f430-49bd-b71d-caa8a0a0b733","cardType":"basic","points":1,"front":"Which satellite orbit passes over both poles and helps monitor the whole planet?","back":"Polar orbit.","mcqOptions":[{"text":"Polar orbit.","correct":true,"explanation":"A polar satellite travels over or near both poles. As Earth rotates underneath its orbit, the satellite can observe the entire planet over time."},{"text":"Geostationary orbit.","correct":false,"explanation":"A geostationary satellite remains above one point on the equator, so it cannot pass over the poles or provide direct coverage of the whole planet."},{"text":"Equatorial orbit.","correct":false,"explanation":"An equatorial orbit stays close to the equator and therefore does not pass over both poles. A polar orbit enables global monitoring."},{"text":"Elliptical orbit.","correct":false,"explanation":"An elliptical orbit is defined by its non-circular shape, not by crossing both poles. Whole-planet monitoring typically uses a polar orbit."}]},{"id":"53d0604d-d3fd-4d3c-99df-810abb4080f8","cardType":"basic","points":1,"front":"In a circular orbit, what about velocity changes even when speed stays constant?","back":"Its direction changes continuously.","mcqOptions":[{"text":"Its direction changes continuously.","correct":true,"explanation":"Velocity includes both speed and direction. In uniform circular motion the speed remains constant, but the direction changes continuously as the object follows the orbit."},{"text":"Its speed changes continuously.","correct":false,"explanation":"Constant speed is specified for this circular orbit, so speed does not change. Velocity changes because the satellite’s direction of motion changes continuously."},{"text":"Its magnitude changes continuously.","correct":false,"explanation":"The magnitude of velocity is speed, which remains constant in uniform circular motion. It is the velocity’s direction that changes continuously."},{"text":"Its kinetic energy changes continuously.","correct":false,"explanation":"With constant mass and speed, kinetic energy remains constant. The satellite’s velocity still changes continuously because its direction changes around the orbit."}]},{"id":"8646b50c-cc85-4ca3-8733-4ee889ed85c6","cardType":"cloze","points":null,"front":"In a circular orbit, gravity provides a [ ] towards the [ ].","back":"In a circular orbit, gravity provides a centripetal force towards the centre.","mcqOptions":[{"text":"In a circular orbit, gravity provides a centripetal force towards the centre.","correct":true,"explanation":"Gravity acts towards the centre of the circular orbit. This inward gravitational force is the centripetal force that continually changes the satellite’s direction."},{"text":"In a circular orbit, gravity provides a centrifugal force towards the centre.","correct":false,"explanation":"Centrifugal force is an apparent outward effect in a rotating reference frame, not the real inward force maintaining an orbit. Gravity supplies centripetal force towards the centre."},{"text":"In a circular orbit, gravity provides a centripetal force towards the tangent.","correct":false,"explanation":"Centripetal force acts towards the centre, not along the tangent. The satellite’s instantaneous velocity is tangential, while gravity accelerates it inwards."},{"text":"In a circular orbit, gravity provides a frictional force towards the centre.","correct":false,"explanation":"Friction is not responsible for maintaining an orbit in space. Gravity acts as the centripetal force directed towards the orbit’s centre."}]},{"id":"c22de502-017f-458d-8bff-70de687371a9","cardType":"basic","points":1,"front":"A satellite moves from a high stable orbit to a lower stable orbit. What happens to its orbital speed?","back":"It becomes higher.","mcqOptions":[{"text":"It becomes higher.","correct":true,"explanation":"A lower stable circular orbit has a smaller radius. Since orbital speed follows $v=\\sqrt{GM/r}$, reducing the orbital radius increases the required speed."},{"text":"It becomes lower.","correct":false,"explanation":"The intuition that moving closer slows a satellite is reversed for stable orbits. A smaller orbital radius requires a higher speed according to $v=\\sqrt{GM/r}$."},{"text":"It remains constant.","correct":false,"explanation":"Orbital speed depends on orbital radius, so it cannot remain constant when moving between stable circular orbits. A lower orbit has a higher speed."},{"text":"It becomes zero.","correct":false,"explanation":"Zero orbital speed would make the satellite fall directly towards Earth rather than remain in a stable orbit. A lower stable orbit requires a higher speed."}]},{"id":"8e06ac8f-9e5d-449d-b73a-0bd5e0b90692","cardType":"cloze","points":null,"front":"A star begins in a [ ]; gravitational collapse forms a [ ].","back":"A star begins in a nebula; gravitational collapse forms a protostar.","mcqOptions":[{"text":"A star begins in a nebula; gravitational collapse forms a protostar.","correct":true,"explanation":"Stars form when gravity draws gas and dust together within a nebula. The collapsing material initially becomes a protostar before nuclear fusion begins in its core."},{"text":"A star begins in a galaxy; gravitational collapse forms a main sequence star.","correct":false,"explanation":"A galaxy contains many stars and nebulae rather than serving as the immediate birthplace of one star. A star begins in a nebula, whose collapse forms a protostar."},{"text":"A star begins in a supernova; gravitational collapse forms a white dwarf.","correct":false,"explanation":"A supernova is the explosive death of a massive star, not its birthplace, while a white dwarf is a stellar remnant. A nebula collapses to form a protostar."},{"text":"A star begins in a protostar; gravitational collapse forms a red giant.","correct":false,"explanation":"A protostar is already an early stage of a forming star, not the original cloud of material. The process begins in a nebula, and collapse produces a protostar."}]},{"id":"3ed4699d-02fd-4c3a-916c-de374f3020ab","cardType":"basic","points":1,"front":"What starts when a protostar's core becomes hot enough?","back":"Nuclear fusion.","mcqOptions":[{"text":"Nuclear fusion.","correct":true,"explanation":"Once the core is sufficiently hot, hydrogen nuclei can overcome their electrostatic repulsion and fuse. Nuclear fusion then releases energy and marks the star’s main sequence stage."},{"text":"Nuclear fission.","correct":false,"explanation":"Nuclear fission splits heavy nuclei and is not the process that powers an ordinary star. A sufficiently hot protostar begins nuclear fusion of light nuclei."},{"text":"Radioactive decay.","correct":false,"explanation":"Radioactive decay occurs spontaneously in unstable nuclei and does not require the extreme core temperature of a protostar. The temperature threshold instead allows nuclear fusion to begin."},{"text":"Chemical combustion.","correct":false,"explanation":"Chemical combustion rearranges electrons and cannot supply a star’s enormous, long-lasting energy output. When the protostar’s core becomes hot enough, nuclear fusion starts."}]},{"id":"bddcda3c-c7bf-410b-8a6e-69b4d18c2b17","cardType":"basic","points":2,"front":"During most of a star's life, which nuclei fuse and what do they form?","back":"Hydrogen nuclei fuse to form helium.","mcqOptions":[{"text":"Hydrogen nuclei fuse to form helium.","correct":true,"explanation":"A main sequence star spends most of its lifetime fusing hydrogen nuclei into helium. This fusion releases the energy that supports the star against gravitational collapse."},{"text":"Helium nuclei fuse to form carbon.","correct":false,"explanation":"Helium fusion occurs only during a later evolutionary stage after core hydrogen becomes scarce. During most of a star’s life, hydrogen nuclei fuse to form helium."},{"text":"Helium nuclei fuse to form hydrogen.","correct":false,"explanation":"Fusion builds heavier nuclei rather than converting helium back into lighter hydrogen nuclei. During the main sequence, hydrogen nuclei fuse to produce helium."},{"text":"Hydrogen nuclei fuse to form carbon.","correct":false,"explanation":"Hydrogen fusion does not produce carbon directly; carbon is formed later through helium fusion. For most of the star’s life, hydrogen nuclei fuse to form helium."}]},{"id":"c09ab06e-4574-46b4-b254-73d3176f3367","cardType":"basic","points":1,"front":"What balances inward gravitational collapse in a main sequence star?","back":"Outward pressure from fusion energy.","mcqOptions":[{"text":"Outward pressure from fusion energy.","correct":true,"explanation":"Fusion releases energy that heats the stellar material and produces outward pressure. In a stable main sequence star, this balances the inward pull caused by gravity."},{"text":"Inward pressure from fusion energy.","correct":false,"explanation":"Fusion energy generates pressure directed outwards, not inwards. This outward pressure balances the inward gravitational force and keeps a main sequence star stable."},{"text":"Outward pressure from chemical energy.","correct":false,"explanation":"Chemical reactions release far too little energy to support a star and are not its energy source. Outward pressure generated by nuclear fusion balances gravitational collapse."},{"text":"Outward pressure from gravitational energy.","correct":false,"explanation":"Gravity produces the inward force that tends to collapse the star, so gravitational energy cannot provide the opposing support. Outward pressure from fusion energy supplies the balance."}]},{"id":"22ea5e72-d28a-43ad-b8c9-095e5a02688a","cardType":"basic","points":3,"front":"For a Sun-like star, what is the route after the main sequence?","back":"

Red giant
Planetary nebula
White dwarf

","mcqOptions":[{"text":"

Red giant
Planetary nebula
White dwarf

","correct":true,"explanation":"After exhausting core hydrogen, a Sun-like star expands into a red giant. It then sheds its outer layers as a planetary nebula, leaving a white dwarf."},{"text":"

Red supergiant
Supernova
Neutron star

","correct":false,"explanation":"A red supergiant, supernova and neutron star belong to the life cycle of a much more massive star. A Sun-like star becomes a red giant, planetary nebula and white dwarf."},{"text":"

Red giant
Supernova
White dwarf

","correct":false,"explanation":"A Sun-like star does become a red giant, but it lacks enough mass to explode as a supernova. It forms a planetary nebula and leaves a white dwarf."},{"text":"

Red giant
Planetary nebula
Neutron star

","correct":false,"explanation":"A planetary nebula is a valid stage, but a Sun-like star’s core does not collapse into a neutron star. The remaining core becomes a white dwarf."}]},{"id":"b04818b0-9520-423f-b0f0-17ecd9cad86e","cardType":"basic","points":3,"front":"For a massive star, what is the route after the main sequence?","back":"

Red supergiant
Supernova
Neutron star or black hole

","mcqOptions":[{"text":"

Red supergiant
Supernova
Neutron star or black hole

","correct":true,"explanation":"A massive main sequence star expands into a red supergiant before its core collapses in a supernova. The remnant becomes a neutron star or, if sufficiently massive, a black hole."},{"text":"

Red giant
Planetary nebula
White dwarf

","correct":false,"explanation":"A red giant, planetary nebula and white dwarf describe the later evolution of a Sun-like star. A massive star instead undergoes a supernova after becoming a red supergiant."},{"text":"

Red supergiant
Planetary nebula
Neutron star or black hole

","correct":false,"explanation":"Massive stars do become red supergiants, but they explode as supernovae rather than gently producing planetary nebulae. Their remnants are neutron stars or black holes."},{"text":"

Red supergiant
Supernova
White dwarf

","correct":false,"explanation":"A white dwarf is the remnant of a lower-mass star, not the usual outcome of a massive star’s supernova. The collapsed remnant is a neutron star or black hole."}]},{"id":"d2707e9c-baf8-4e00-a927-9d72099902cd","cardType":"basic","points":1,"front":"At ordinary temperatures, what radiation do objects mainly emit?","back":"Infrared radiation.","mcqOptions":[{"text":"Infrared radiation.","correct":true,"explanation":"Objects at ordinary temperatures emit thermal radiation primarily in the infrared region. They are not hot enough for the peak of their emission to lie in visible wavelengths."},{"text":"Visible light.","correct":false,"explanation":"Ordinary objects can reflect visible light, but their own thermal emission is mainly infrared. Visible emission becomes significant only when an object reaches much higher temperatures."},{"text":"Microwave radiation.","correct":false,"explanation":"Microwaves have longer wavelengths than the peak thermal emission from objects at typical everyday temperatures. Such objects mainly emit infrared radiation."},{"text":"Ultraviolet radiation.","correct":false,"explanation":"Ultraviolet radiation is associated with much hotter objects because its wavelengths are shorter and its photons more energetic. Ordinary-temperature objects mainly emit infrared radiation."}]},{"id":"26fe6cb7-3b3b-4a3a-9191-f108569683b7","cardType":"cloze","points":null,"front":"As temperature increases, emitted radiation has greater [ ] and a shorter [ ].","back":"As temperature increases, emitted radiation has greater total intensity and a shorter peak wavelength.","mcqOptions":[{"text":"As temperature increases, emitted radiation has greater total intensity and a shorter peak wavelength.","correct":true,"explanation":"A hotter object emits more energy per unit area, increasing the total intensity. Wien’s displacement law also shows that its emission peak shifts to a shorter wavelength."},{"text":"As temperature increases, emitted radiation has greater surface area and a shorter peak wavelength.","correct":false,"explanation":"Temperature does not cause an object’s emitting surface area to increase automatically. It increases total intensity, while the peak of the emission spectrum moves to a shorter wavelength."},{"text":"As temperature increases, emitted radiation has greater total intensity and a shorter emission duration.","correct":false,"explanation":"Although total intensity increases with temperature, the duration of emission is not set by temperature in this relationship. The spectral peak instead shifts to a shorter wavelength."},{"text":"As temperature increases, emitted radiation has greater surface area and a shorter emission duration.","correct":false,"explanation":"Heating does not necessarily increase the object’s surface area or shorten how long it emits. It increases total intensity and shifts the peak to a shorter wavelength."}]},{"id":"a914b6cf-2d51-4c57-a195-ba0149aa7172","cardType":"basic","points":1,"front":"If an object absorbs radiation faster than it emits radiation, what happens to its temperature?","back":"It rises.","mcqOptions":[{"text":"It rises.","correct":true,"explanation":"Absorbing radiation transfers energy to the object faster than emission removes it, so its internal energy increases and its temperature rises."},{"text":"It falls.","correct":false,"explanation":"A falling temperature would require the object to emit radiation faster than it absorbs it. Here there is a net energy gain, so its temperature rises."},{"text":"It stays constant.","correct":false,"explanation":"Constant temperature requires equal rates of radiation absorption and emission. Absorption is faster in this case, so the object gains energy and its temperature rises."},{"text":"It fluctuates.","correct":false,"explanation":"Unequal absorption and emission rates produce a definite net energy transfer, not necessarily repeated variation. Faster absorption causes the object’s temperature to rise."}]},{"id":"6e416a03-e9d8-40bd-b50f-5c61046d36a6","cardType":"basic","points":2,"front":"How do greenhouse gases change Earth's infrared radiation balance?","back":"They absorb and re-emit some infrared from Earth's surface.","mcqOptions":[{"text":"They absorb and re-emit some infrared from Earth's surface.","correct":true,"explanation":"Greenhouse gases absorb some outgoing infrared radiation and re-emit it in all directions, reducing the rate at which energy escapes from Earth to space."},{"text":"They transmit all infrared directly into space from Earth's surface.","correct":false,"explanation":"Greenhouse gases do not simply transmit all outgoing infrared into space. They absorb and re-emit some surface infrared, which slows Earth’s loss of thermal energy."},{"text":"They absorb and re-emit some visible light from Earth's surface.","correct":false,"explanation":"This confuses incoming visible radiation with outgoing infrared radiation. Greenhouse gases mainly affect the balance by absorbing and re-emitting some infrared from Earth’s surface."},{"text":"They reflect all infrared back downwards from Earth's surface.","correct":false,"explanation":"Greenhouse gases absorb and re-emit infrared rather than reflecting all of it. Some re-emitted radiation travels towards space and some returns towards Earth’s surface."}]},{"id":"0257d38f-1343-4089-855f-474e1030ef89","cardType":"cloze","points":null,"front":"Red-shift means light has increased [ ] and decreased [ ].","back":"Red-shift means light has increased wavelength and decreased frequency.","mcqOptions":[{"text":"Red-shift means light has increased wavelength and decreased frequency.","correct":true,"explanation":"Red-shift moves spectral lines towards longer wavelengths. Since wave speed equals frequency multiplied by wavelength and light’s speed is constant, the frequency decreases."},{"text":"Red-shift means light has increased frequency and decreased wavelength.","correct":false,"explanation":"This reverses the changes associated with red-shift and instead describes blue-shift. Red-shift gives an increased wavelength and a decreased frequency."},{"text":"Red-shift means light has increased wavelength and decreased speed.","correct":false,"explanation":"Light’s speed in a vacuum remains constant during cosmological red-shift. Its wavelength increases while its frequency decreases, preserving the relationship $c=f\\lambda$."},{"text":"Red-shift means light has increased amplitude and decreased frequency.","correct":false,"explanation":"Amplitude determines the wave’s intensity rather than its position in the spectrum. Red-shift specifically means that wavelength increases and frequency decreases."}]},{"id":"fe3a10fc-fab5-4b56-8aa0-a1361164c9f6","cardType":"basic","points":1,"front":"What does a larger red-shift in a galaxy's light show?","back":"The galaxy is receding faster.","mcqOptions":[{"text":"The galaxy is receding faster.","correct":true,"explanation":"A larger red-shift means a greater increase in observed wavelength. Through the Doppler effect, this indicates that the galaxy is moving away at a higher speed."},{"text":"The galaxy is approaching faster.","correct":false,"explanation":"A galaxy approaching Earth produces a blue-shift, not a red-shift. A larger red-shift indicates that the galaxy is receding faster."},{"text":"The galaxy is receding more slowly.","correct":false,"explanation":"A slower recession would produce a smaller red-shift, assuming the usual velocity-distance interpretation. A larger red-shift shows that the galaxy is receding faster."},{"text":"The galaxy is remaining stationary.","correct":false,"explanation":"A stationary galaxy would show no Doppler shift from relative motion. A larger red-shift instead indicates increasingly rapid motion away from the observer."}]},{"id":"69c303d8-4f81-4323-9a9d-315963137167","cardType":"basic","points":1,"front":"What red-shift pattern is evidence that the universe is expanding?","back":"More distant galaxies usually have greater red-shift.","mcqOptions":[{"text":"More distant galaxies usually have greater red-shift.","correct":true,"explanation":"Observations show that red-shift generally increases with a galaxy’s distance. This relationship indicates that distant galaxies recede faster, supporting an expanding universe."},{"text":"More distant galaxies usually have smaller red-shift.","correct":false,"explanation":"This reverses the observed relationship between distance and red-shift. More distant galaxies generally show greater red-shift, indicating faster recession in an expanding universe."},{"text":"Nearby galaxies usually have greater red-shift.","correct":false,"explanation":"Nearby galaxies do not generally have the greatest red-shifts. The expansion pattern is that more distant galaxies usually show greater red-shift and faster recession."},{"text":"All observed galaxies usually have equal red-shift.","correct":false,"explanation":"Red-shift is not generally independent of distance. Its tendency to increase for more distant galaxies provides evidence that the universe is expanding."}]},{"id":"f99326e0-75c6-4646-b453-96c86e87222d","cardType":"basic","points":1,"front":"In the Big Bang model, what has the universe done since its hot, dense beginning?","back":"It has expanded and cooled.","mcqOptions":[{"text":"It has expanded and cooled.","correct":true,"explanation":"The Big Bang model describes space expanding from an initially hot, dense state. Expansion caused the universe’s matter and radiation to spread out and cool."},{"text":"It has contracted and heated.","correct":false,"explanation":"Contraction would make matter denser and generally hotter, contrary to evidence for increasing galactic separation. Since its hot, dense beginning, the universe has expanded and cooled."},{"text":"It has expanded and heated.","correct":false,"explanation":"Although the universe has expanded, expansion reduces the energy of radiation and lowers the average temperature. It has therefore expanded and cooled, not heated."},{"text":"It has remained static and cooled.","correct":false,"explanation":"Observations of galactic red-shift show that the universe has not remained the same size. It has expanded, and its average temperature has decreased as a result."}]},{"id":"8c9f9eda-2181-49f0-86f7-21a4b4beb3d2","cardType":"cloze","points":null,"front":"[ ] is detected from all directions and is cooled leftover radiation from the [ ].","back":"Cosmic microwave background radiation is detected from all directions and is cooled leftover radiation from the early universe.","mcqOptions":[{"text":"Cosmic microwave background radiation is detected from all directions and is cooled leftover radiation from the early universe.","correct":true,"explanation":"Cosmic microwave background radiation arrives from every direction and has the thermal spectrum expected of radiation stretched and cooled by expansion since the early universe."},{"text":"Cosmic infrared background radiation is detected from all directions and is cooled leftover radiation from the early universe.","correct":false,"explanation":"The relic radiation has cooled into the microwave region, not the infrared region. Cosmic microwave background radiation is leftover radiation from the early universe."},{"text":"Cosmic microwave background radiation is detected from all directions and is cooled leftover radiation from the Earth's atmosphere.","correct":false,"explanation":"The nearly uniform microwave background is not produced by Earth’s atmosphere. It comes from all directions in space and is cooled leftover radiation from the early universe."},{"text":"Cosmic X-ray background radiation is detected from all directions and is cooled leftover radiation from the Earth's atmosphere.","correct":false,"explanation":"X-ray background radiation is associated with energetic astrophysical sources, not the cooled Big Bang remnant. The relevant radiation is the cosmic microwave background from the early universe."}]},{"id":"1436bb95-4307-4998-b237-385e2ef6c551","cardType":"basic","points":1,"front":"What does the failure of S waves to pass through Earth's outer core show?","back":"The outer core is liquid.","mcqOptions":[{"text":"The outer core is liquid.","correct":true,"explanation":"S waves are transverse seismic waves and cannot travel through liquids. Their disappearance at the outer core boundary therefore shows that the outer core is liquid."},{"text":"The inner core is liquid.","correct":false,"explanation":"The inner core is solid, as shown by other seismic evidence. S waves disappear on entering the outer core because that layer, rather than the inner core, is liquid."},{"text":"The outer core is solid.","correct":false,"explanation":"S waves can pass through solids, so a solid outer core would not explain their failure to pass through it. Their absence shows that the outer core is liquid."},{"text":"The mantle is liquid.","correct":false,"explanation":"Although parts of the mantle can flow slowly, it behaves as a solid for seismic waves and transmits S waves. Their blockage shows that the outer core is liquid."}]},{"id":"9f0224ac-eacd-46d7-8c75-db3f652d2d34","cardType":"basic","points":2,"front":"Sonar pulse speed is 1500 m/s; echo returns after 0.12 s. What is the seabed depth?","back":"90 m.","mcqOptions":[{"text":"90 m.","correct":true,"explanation":"The pulse travels to the seabed and back, so the depth is half the total distance: $\\frac{1500 \\times 0.12}{2} = 90$ m."},{"text":"180 m.","correct":false,"explanation":"This uses the full return time for a one-way journey. The calculated 180 m is the total distance travelled, so halving it gives the correct depth of 90 m."},{"text":"45 m.","correct":false,"explanation":"This halves the travel time twice rather than once. The echo’s 0.12 s covers both directions, so the depth is $1500 \\times 0.12 \\div 2 = 90$ m."},{"text":"12,500 m.","correct":false,"explanation":"This comes from dividing speed by time instead of multiplying them. Distance equals speed multiplied by time, then the round-trip distance must be halved, giving 90 m."}]}]}],"examCountdown":{"examDate":"2027-05-25","paperLabel":"Paper 1"},"heading":"Beyond Earth","title":"Beyond Earth Flashcards","topbar":{"backHref":"/gcse/physics/ocr/flashcards"},"topicSidebar":"$L37"}]}],"topicId":"e6a05d67-2c0b-5412-a7d1-78b35957f51c","walled":"$L38"}],"$L39","$L3a"]