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45 Cards in this Set

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Equation for density?
Density = mass/ volume
What is density?
Density relates mass of a substance to how much stuff it takes up
What does the density of an object depend on?

What it is made of


Doesn't vary with size or shape

What determines if an object floats or sinks?

It's average density


Solid object will float on a fluid if it has a lower density than the fluid.

How to find the mass & volume of regularly shaped objects?

Find mass using balance/scales


Find volume using geometry

How to find mass & volumeof irregularly shaped objects?

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

How to find mass & volumeof a liquid?

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.

Why is no device 100% efficient? (exception to electric heaters)
Energy usually wasted as heat

What are heat exchangers used for?
To reduce the amount of energy wasted by a machine. They pump a cool fluid through the escaping heat & use it for other purposes.
Direction of vibrations in transverse waves?
Vibrations are perpendicular to direction of energy transfer

Direction of vibrations in longitudinal waves?
Vibrations are parallel to direction of energy transfer
3 examples of transverse waves?

EM waves


S waves


Waves on springs

4 examples of longitudinal waves?

P waves


Slinky springs


Sound waves


Ultrasound

How to find wavespeed?
Wavespeed= frequency (Hz) x wavelength (m)

What direction is light refracted when passing from air to glass? What happens to its speed?

Light slows down so refracts towards the normal

What direction is light refracted when passing from glass to air? What happens to its speed?
Light speeds up so refracts away from the normal
What affects the change in refraction?
Greater the change in speed, the greater the refraction

What affect does reflection have on light?
Changes its direction but not its speed, wavelength or frequency
What is the speed of all EM Waves in a vacuum?
3 x 10 ^8 m/s
Speed of sound through solids liquids & gases?
Solids > liquids > gases
What waves can cause ionisation?
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
What factors affect the rate of conduction?

Materials


State of material


Surface area


temp difference ( the greater the temp difference between 2 touching objects, the higher the rate of conduction)

Tell me about evaporation

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.

How to increase rate of evaporation?

- 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

What is electric current?
Flow of charge
Electron movement with polythene rod?
Electrons move from duster to rod
Electron movement with acetate rod?
Electrons move from rod to duster
Affect of increasing current on resistance?
Increasing current - increases temp. - particles vibrate more- increases resistance- decreases current
Equation for current & charge?
current = charge / time
Current of fixed resistor?

Current through fixed resistor at constant temp is directly proportional to PD ( hence straight line on graph).



IV graph of filament lamp?
As temp. of filament increases, the resistance increases (causes curve on graph)
PD in a series circuit?

PD is shared


Total work done on the charge by battery must equal total work done by charge on components



Current in a series circuit?
Same current flows through all parts of the circuit
Resistance in a series circuit?
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.
PD in a parallel circuit?
PD same across all components
Current in a parallel circuit?

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.

Resistance in parallel circuits?

1/R = 1/R1 + 1/R2 etc.


Total resistance is always less than that of the branch with the smallest resistance

What is electromagnetic induction?
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.

Effect of turning a magnet end to end in a coil of wire?

Magnetic field through coil changes, which induces a PD which makes current flow in wire.



What happens when magnet turned 1/2 a turn?

Direction of magnet field through coil reverses so PD reverse & current flows in opposite direction.


Keep doing this to get AC!

What factors affect the size of induced voltage?

- Strength of magnet


- Area of coil


- No. of turns on coil


- Speed of movement

What is the transformer equation?

For a transformer with 100% efficiency:


vp/vs = np/ns



Power loss due to resistance?
P= I^2 R
Power in relation to transformers for 100% efficieny?

Power supplied to transformer = power delivered by transformer


therefore Vp x Ip = Vs x Is

What does a flat section on a VT graph represent?
Constant speed