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45 Cards in this Set
- Front
- Back
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Equation for density?
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Density = mass/ volume
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What is density?
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Density relates mass of a substance to how much stuff it takes up
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What does the density of an object depend on?
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What it is made of Doesn't vary with size or shape |
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What determines if an object floats or sinks?
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It's average density Solid object will float on a fluid if it has a lower density than the fluid. |
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How to find the mass & volume of regularly shaped objects?
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Find mass using balance/scales Find volume using geometry |
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How to find mass & volumeof irregularly shaped objects?
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Find mass using balance Find volume by dropping object into beaker of water, change in volume of water is the same as the volume of the object |
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How to find mass & volumeof a liquid?
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Find mass by measuring the mass of an empty beaker, then the mass of liquid + beaker. Mass of liquid is the same as the change in mass. Find volume by reading off a scale. |
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Why is no device 100% efficient? (exception to electric heaters)
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Energy usually wasted as heat
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What are heat exchangers used for?
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To reduce the amount of energy wasted by a machine. They pump a cool fluid through the escaping heat & use it for other purposes.
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Direction of vibrations in transverse waves?
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Vibrations are perpendicular to direction of energy transfer
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Direction of vibrations in longitudinal waves?
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Vibrations are parallel to direction of energy transfer
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3 examples of transverse waves?
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EM waves S waves Waves on springs |
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4 examples of longitudinal waves?
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P waves Slinky springs Sound waves Ultrasound |
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How to find wavespeed?
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Wavespeed= frequency (Hz) x wavelength (m)
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What direction is light refracted when passing from air to glass? What happens to its speed? |
Light slows down so refracts towards the normal
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What direction is light refracted when passing from glass to air? What happens to its speed?
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Light speeds up so refracts away from the normal
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What affects the change in refraction?
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Greater the change in speed, the greater the refraction
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What affect does reflection have on light?
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Changes its direction but not its speed, wavelength or frequency
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What is the speed of all EM Waves in a vacuum?
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3 x 10 ^8 m/s
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Speed of sound through solids liquids & gases?
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Solids > liquids > gases
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What waves can cause ionisation?
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Only UV, X-ray & Gamma because they have high energy and so can remove an electron, changing the atom or molecule into a charged ion
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What factors affect the rate of conduction?
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Materials State of material Surface area temp difference ( the greater the temp difference between 2 touching objects, the higher the rate of conduction) |
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Tell me about evaporation
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Evaporation = liquid to gas Occurs if particles travelling in right direction to escape liquid & if travelling fast enough (so with enough KE) to overcome the attractive forces of other particles in the liquid. Faster particles (with most KE) most likely to escape - average speed & KE of remaining particles decreases to temp. of remaining liquid falls. |
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How to increase rate of evaporation?
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- Temp higher ( average KE of particles is higher) - Density is lower (forces between particles will be lower) - SA larger (more particles nearer surface to escape) - Airflow over liquid is greater OPPOSITE FOR INCREASING RATE OF CONVECTION |
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What is electric current?
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Flow of charge
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Electron movement with polythene rod?
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Electrons move from duster to rod
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Electron movement with acetate rod?
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Electrons move from rod to duster
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Affect of increasing current on resistance?
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Increasing current - increases temp. - particles vibrate more- increases resistance- decreases current
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Equation for current & charge?
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current = charge / time
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Current of fixed resistor?
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Current through fixed resistor at constant temp is directly proportional to PD ( hence straight line on graph). |
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IV graph of filament lamp?
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As temp. of filament increases, the resistance increases (causes curve on graph)
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PD in a series circuit?
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PD is shared Total work done on the charge by battery must equal total work done by charge on components |
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Current in a series circuit?
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Same current flows through all parts of the circuit
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Resistance in a series circuit?
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Total resistance is sum of individual resistances. Bigger the resistance of a component, the bigger its share of total PD because more work is done by the charge when moving through a larger resistance than a smaller one. If resistance of 1 component changes, PD across ALL components changes.
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PD in a parallel circuit?
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PD same across all components
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Current in a parallel circuit?
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Current shared between branches. 2 identical components connected in parallel will have the same current flowing through them. Total current flowing around circuit = sum of current through all components. |
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Resistance in parallel circuits?
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1/R = 1/R1 + 1/R2 etc. Total resistance is always less than that of the branch with the smallest resistance |
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What is electromagnetic induction?
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Creation of a PD across a conductor which is experiencing a change in magnetic field <-- can do this by moving a magnetic in a cold of wire.
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Effect of turning a magnet end to end in a coil of wire?
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Magnetic field through coil changes, which induces a PD which makes current flow in wire. |
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What happens when magnet turned 1/2 a turn?
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Direction of magnet field through coil reverses so PD reverse & current flows in opposite direction. Keep doing this to get AC! |
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What factors affect the size of induced voltage?
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- Strength of magnet - Area of coil - No. of turns on coil - Speed of movement |
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What is the transformer equation?
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For a transformer with 100% efficiency: vp/vs = np/ns |
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Power loss due to resistance?
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P= I^2 R
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Power in relation to transformers for 100% efficieny?
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Power supplied to transformer = power delivered by transformer therefore Vp x Ip = Vs x Is |
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What does a flat section on a VT graph represent?
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Constant speed
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