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78 Cards in this Set
- Front
- Back
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Life cycle of a small star |
Nebula》Protostar》Main sequence star》Red giant》White dwarf》Black dwarf |
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Life cycle of a big star |
Nebula》Protostar》Main sequence star》Red super giant》Supernova》Neutron star/black hole |
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What happens to a star before it explodes in a supernova |
It expands and contracts several times |
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How are elements heavier than iron formed |
In a supernova |
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What is the solar system |
All the stuff that orbits our sun |
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What is happening to an object orbiting an object |
-Constantly changing direction, velocity and so acceleration -Not changing speed |
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Force diagram for an object in orbit |
-Object already moving so changes direction |
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What happens to an object if it's placed in a lower - radius orbit |
-Orbital speed increases -Due to force of gravity increasing as closer to earth -So larger force acts -Instantaneous speed would not increase for stable orbit |
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Evidence for the universe expanding |
-Wavelengths of light from distance galaxies increased -Shifted to red of spectrum, called red-shift -Suggests source is moving away from us -More distant galaxies = Greater red - shifts so moving away from us faster |
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Big bang theory |
-At the start all matter occupied a small space, which was very dense and hot -It exploded - Space started expanding + still expanding |
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What causes rise in tempreture that leads to fusion in a protostar |
Star gets denser so more particles collide with eachother |
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Why is a main sequence star stable for a long time |
Outward pressure created by nuclear fusion that tries to expand the star balances the force of gravity pulling inwards |
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How is a black dwarf made |
By having a white dwarf cool down |
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What do planets and dwarf planets orbit |
A star |
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Which galaxy is our solar system a part of |
the Milky Way galaxy |
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Direction of object's instantaneous velocity in relation to the gravitational force |
Perpendicular |
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2 limitations of the balloon model of the expanding universe |
-Balloons have a limit to how much they can stretch -No galaxies inside the balloon |
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What did scientists discover about the movement of galaxies in 1998 and how did they discover this |
-Distant galaxies moving away from us faster and faster (Speed at which receding increasing) -Known by observing supernovae from 1998 to present day |
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Why are red giants red |
Because their surface cools |
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What is a magnetic field |
A region where other magnetic materials experience a force |
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Magnetic field for a bar magnet image |
-Lines show direction of force if a north pole was put at that point -Strongest at poles (So forces also strongest) |
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Force between a magnet and a magnetic material |
Always attractive |
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Image for 2 like poles |
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Image for 2 unlike poles |
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How to find the magnetic field of a material |
North pole of magnet in compass is attracted to south pole |
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Why do compasses not inside a magnetic field always point north |
-Earth generates own magnetic field -Showing core must be magnetic |
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What are permanent magnets |
Magnets that produce their own magnetic field |
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What are induced magnets |
Magnetic materials that turn into a magnet when put in a magnetic field |
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Force between permanent + induced magnets |
Always attractive |
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What happens when you take away the magnetic field of an induced magnet |
-Lose their magnetism -Stop producing a magnetic field |
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2 differences between permanent and induced magnets |
-Permanent produce own magnetic fields, induced become magnetised when in field -Force induced-permanent = Attractive, permanent-permanent = Attractive/repulsive |
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Current in a wire and magnetic field |
State 'current out of page' and draw 2D bird's eye view |
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3 ways to change the magnetic field of a wire with moving charge |
-Change direction of current -Increase current -Move closer to wire |
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Solenoid |
-Wire wrapped in a coil -Magnetic field in solenoid is strong+uniform -Outside is like a bar magnet |
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Why does wrapping a wire in a solenoid increase the strength of the magnetic field |
-Field lines around each loop of wire line up -So lots of field lines pointing in the same direction + close to each other |
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Why does putting a block of iron in a solenoid centre increase the field strength |
Iron core becomes an induced magnet whenever current is flowing |
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What is a solenoid with an iron core called |
An electromagnet |
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Why are electromagnets useful |
-Quick to turn on and off -Can create a varying force |
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3 uses of electromagnets |
-Speakers -Cranes - To pick stuff up -Switches - In other circuits |
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What is the motor effect |
-Current-carrying wire (Conductor) put between magnetic poles -Magnetic field around wire interacts with magnetic field placed in -So magnet and conductor (current-carrying wire) exert a force on each other |
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Direction of force in relation to magnetic field+direction of current |
At right angles |
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How to increase force in the motor effect |
-Put wire 90° to magnetic field - If parallel to field no force+ some force if at angles between -Increase strength of magnetic field -Increase current through conductor |
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Equation for force acting on a conductor in a magnetic field |
Force (N) = Magnetic flux density (T)(field lines) x Current (through conductor) x Length (m)(of conductor in a magnetic field) |
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Fleming's left hand rule |
-Left hand |
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How does a motor work |
-2 side arms receive opposite force -Split-ring commutator swaps contacts every half turn to make the motor rotate in the same direction |
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2 ways to reverse direction of motor |
-Swapping polarity of d.c. supply (reversing current) -Swapping magnetic poles (reversing field) |
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Motor |
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How does a speaker work |
-A.c. sent through a coil of wire attached to the base of a paper cone -Force on coil from magnet so it moves -Current reverses = Force acts in opposite direction = Cone moves in opposite direction -So cone vibrates - creating pressure in air making a sound wave -Frequency sound wave = frequency a.c. - So can alter sound wave produced |
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Speaker |
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How is a p.d. induced |
By cutting field lines |
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What is induced in the generator effect if a complete circuit is made |
Current |
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What is the generator effect |
The induction of a p.d. (And current if a complete circuit) in a wire that is moving relative to a magnetic field, or experiencing a change in magnetic field |
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2 ways to use the generator effect |
-Move a magnet in a coil of wire -Move a conductor (wire) in a magnetic field |
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2 ways to reverse p.d. in the generator effect |
-Move magnet/conductor in opposite direction -Reverse polarity of magnet |
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How to produce a.c. using the generator effect |
Keep moving magnet/coil backwards and forwards |
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How to produce an a.c. with a coil and a magnet |
-Spin magnet end to end -As it is turned, the magnetic field changes -So inducing a p.d. -When through half a turn the magnetic field reverses so p.d. + current flow in opposite direction -If repeated a.c. is created |
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Why does an induced current always oppose the change that made it |
The magnetic field always goes against the change that made it |
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2 ways to increase induced p.d. in a generator |
-Increasing speed of movement (of a conductor or magnet) -Increasing strength of magnetic field |
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Generators for a.c. |
Alternators |
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Generators for d.c. |
Dynamos |
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Alternator |
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How does an alternator work |
-A coil is rotated in a magnetic field -As coil spins, current is induced which changes direction every half turn -So a.c. produced |
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Dynamo |
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How does a dynamo work |
-A coil is rotated in a magnetic field -As coil spins, current is induced -Split-ring commutator swaps connection every half turn so current flows in the same direction |
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Device to see generated p.d. |
Oscilloscope |
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a.c. trace with increasing revolutions |
-Increases overall p.d. -Increases number of peaks |
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How does a microphone work |
-Sound wave hit flexible diaphragm -Attached to coil of wire (wrapped around a magnet) -Coil of wire moves in the magnetic field, generating current -Movement of coil depends on properties of sound wave |
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What do transformers do |
Change the size of the p.d. of a.c. |
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Why is iron used in transformers |
Because it's easily magnetised |
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How does a transformer work |
-Iron core magnetises + demagnetises quickly -This change in magnetic field induced an alternating p.d. in secondary coil -If second coil is part of a complete circuit, a current is induced |
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Turns in a step-up transformer |
More on secondary coil than primary |
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Turns in a step-down transformer |
More on primary than secondary |
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Transformer equation |
Input p.d. Primary turns ---------------- = -------------------- Output p.d. Secondary turns |
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Current + p.d. in a transformer equation |
-VsIs = VpIp -Assumes input power = output power |
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4 magnetic materials |
-Iron -Steel -Nickel -Cobalt |
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Magnetic field for a magnet inside loudspeaker |
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Direction of current flow |
Positive 》Negative |
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How does it work |
Switch closed》Electromagnet on》Attracts iron contact on rocker -Rocker pivots》Closes contracts》Circuit 2 complete》Motor turning |
