hard questions Flashcards
define acceleration
change in velocity per unit time
explain one other way in which the air leaving the condenser is different
from the air entering the condenser
air is drier leaving because water vapour condenses
unit for impulse or momentum
Ns
The lid is removed from the bottle.
State and explain how the air pressure inside the bottle changes.
volume increases, air moves out of bottle, pressure decreases, until equal to pressure outside of bottle
Suggest why a Bluetooth headset only works well over short distances
radio waves lose energy get weaker with distance
Describe the mass and energy changes that take place during this process in a nuclear reactor. (nuclear fission)
nucleus converted into two smaller nuclei, smaller total mass, as converted into kinetic energy, energy increases
Describe how thermal energy from nuclear reactions is used to generate electricity in a power station.
(thermal energy-achieved from geothermal, nuclear reactions or heat from sun, or burning fossil fuels) used to heat / boil (cold) water OR make steam
* steam is at high pressure
* steam drives a turbine
* turbine (connected to and) drives a generatordue to its store of ke formed from spinning
* this turns coil of wire inside generator, moves a coil in a magnetic field producing electricity
* After the steam has spun the turbine, it is cooled in a condenser and re-enters the boiler system as water to be used again.
A protostar becomes a stable star when
inward force caused by gravitational attraction, is balanced equal to outward force caused by high temp of core
explain deacceleration
negative acceleration, decreasing velocity per unit time, rate of change in velocity
suggest one reason why a car wont start decelerating in 0 sec
thinking (reaction time) car will continue to travel at initial speed
why is deacceleration of the car greater than force over mass
air resistence acts in opposite direction to motion
why is the deacceleration of the car not constant
air resistence drag decreases with decreasing speed
resistive force changes
slow speed= bigger drag
state the form of energy stored in the water reservoir used to generate energy
gravitational
water flows to the turbine through a pipe of constant corss sectional area, explain why ke of water in the pipe remains constant as it flows through pipe
as cross sectional area is constant, volume is constant to ke= 1/2 mvˆ2, speed doesnt change as velocity and mass is constant, no changes made to pressure because temperature and area is constant
explain in terms of molecules how evaporation cools water in cloth
molecule with most ke escape surface of liquid/ cloth, molecules left have less avergae ke, cooling down temp in cloth, as they move slower. Ke is porportional to temp, thus temperature falls with decreasing ke
a sound wave has frequency of 1.5 MHz state and explain what type of sound wave it is
ultrasound, frequency above 20000 hz, above audible range
explain in terms of forces and motion of air molecules the cause of the motion of smoke particles
smoke particles constantly hit by small fast moving light air molecules, moving randomly, they exert a force due to change in momentum thus smoke particles appear to be moving in random directions in addition the smoke particles are larger heavier and slower.
state two ways in which transverse waves differ from longitudinal
transeverse waves are made up of crests and peaks, longitudinal made up of compressions and rarefractions
particles on a transverse wave ossillate perpindicular to wave direction/ energy propagation
typical speed of sound in water
1200 m/s- 1500 m/s
state one difference between emf and p.d
e.m.f= chemical to electrical energy
p.d= electrical to heat energy
state and explain which feature in a speed time graph shows acceleration
gradinet= rise/ run = change in speed/ change in time
state and explain acceleration in speed time graph where line is horizontal to x axis
acceleration= 0 because gradient= 0
suggest how does a train ahving a streamlined shape help to travel in high speed
decreases amount of air resistence it experiences
train took 80s to reduce speed from 84-42 m/s explain why with same braking force train takes more than 80s to reduce speed from 42 to zero m/s
slower the speed= less air resistence it experiences, meaning less force helping to slow train down= more time taken to slow it down
on wet day train travels a greater distance before stoping along tacks, train has same speed
friction between rail and train is reduced, train slides, takes more time to slow down thus bigger distance
explain function of piece of iron in transformer
links magnetic field of coils
better induction outlet
stronger magnetic field in secondary
how do you convert m…
m= milli
divide by 1000
state and explain an essential safety feature required for a transformer mounted in a metal case
metal case must be earthed in case wire falls off and insulation fails, or live wire touches case
equation that connects charge and number of electrons
number of electrons= charge/ charge on 1 electron
lead cylinder has a narrow central hole, radioactive source is passed through it, state and explain effect of the lead cylinder on radioactive source
beam of radiation is narrow and straight, radiation in other directions is absorbed
explain why force on ship due to ships engine is greater than calculated value
there is backward drag force
suggest and explain what happens to hydraulic press when some air enters oil
less force produced, due to fact that air can be compressed, some energy used to do that
what is a practical use for a thermistor
fire alarms
why does a swimmer crossing a river producing a constant forward force move at constant speed
forward force produced by swimmer, is balanced with backward force produced by drag or water resistance, of river bank
what happnes to velocity when motorcyle traveling around a bend at constant speed
change in velocity because of change in direction
explain why there must be a resultant force on motorcyclist as she travels around the bend
there is an acceleration,
change in momentum
force is perpendicular to motion
explain why ray of light does not change direction when it enters the block side
angle of incedence= 0 and angle of refraction=0 thus no refraction takes place
differences between digital and analogue waves
analogue waves are over a range owtte
digital consists of two values owtte
state advantages of using digital signals rather than analogue
data transmitted over longer distances
larger rate of data transmission
noise easily removed
what and how do we correct with converging lens
long sightedness, reduce focal length of eye, and focus/ converges light rays on to the back of the retina
why are infrared and visible radiation used in glass optical fibres
carry high rate of data
both are visible as glass is transparent to both visible and infrared radiation
what is the relationship between earth and juptiers density
jupiter has a lower density because made of gas, earth has a high density because its made of solid
what is the relationship between earth and jupiters gravitational field strength
jupiter has a larger mass than earth, because its volume is larger even though its density is smaller, therefore it has a bigger gravitational field strength
what is one measurment taken when determining the speed at which a galaxy is moving away from earth
redshift/ change in wavelength
how the distance of a far galaxy can be determined without using hubles constant
determining the brightness of a supernova in that galaxy
current voltage graph of a filament lamp and explain its shape
voltage=x axis
current= y axis
so curve downwards
as current increases lamp gets hotter increase in resistance, more voltage required for same increase in current owtte
state typical half life of alpha radioactive source
10-500 years
state typical half life for beta radioactive source
any number ofyears eg 20 years
why is beta used to measure thickness of aluminium strips in factory
absorption of beta radioactivity depends of thickness of aluminium strip
unit for hubbles constant
per second
containers with greater mass are loaded near bottom of ship, explain effect on stability
lower centre of gravity, means more stable
define unit kWh
energy transferred in one hour at a rate of transfer of 1kw
state two ways in which boiling differns from evaporation
boiling only in fixed temperature
boiling thorughout liquid
what is emant by compression and rarefraction
particles closer together, region with higher particle density, higher pressure
particles further apart, region with lower particle density, lower pressure
define potential difference
work done per charge through a component
explain what happens to a circuit with a lamp with increase in temp of thermistor
resistance decreases, bigger voltage supplied, bright lamp
state and explain what happens to a dc motor without a split ring or commutator when coil is vertical
turning effect is zero,
so coil stops and goes back way it came
explain nuclear fission
large unstable nucleus splits into two smaller ones, releasing energy
explain what is meant by redshift
increase in wavelength, of a galaxy moving away from earth
state two conditions necessary for helicopter to remain in equilibrium
no resultant net force
no resultant net moment
explain in terms of forces change in motion of a parchutist
intital acceleration due to weight
air resistance increases as speed increases
resultant force downward/acceleration decreases
constant speed when air resistance= weight
explain what is meant by absolute 0
particles have least kinetic energy, lowest possible temperautre
what is meant by a magnetic field
region i which a magnetic pole experiences a force
define direction of a magnetic field
direction of force on north pole
charge of alpha and charge of beta
charge on alpha= 3.2 * 10ˆ-19
beta= 1.6 * 10ˆ-19
safety precautions when moving or storing radioactive sources
limit exposure time
increase distance from source
store in lead box
use tongs or gloves
state what r and t in orbital speed equation for a planet mean
r= orbital radius
t= period
State the main source of energy for tidal energy
moon
State advantages and disadvantages of tidal power as an energy resource.
any one advantage from:
* renewable
* reliable or predictable
* running cost low
* does not produce (harmful) pollution.
any one disadvantage from:
* (high) cost of construction
* possible effects on (marine) life
* not available all day
* power produced doesn’t always match with peak demand
* limited number of sites
* maintenance difficult /increased corrosion (because underwater)
This isotope of sodium has a half-life of 15 hours. The isotope of magnesium is stable
and does not undergo radioactive decay.
Suggest why these properties of the isotope of sodium and the isotope of magnesium
make this isotope of sodium suitable to detect leaks from water pipes.
half life of sodium is long enough
decays into something stable, meaning less hazardous to humans
State and explain the main process by which thermal energy is transferred to the worker standing beside a hot metal block
radiation
electromagnetic / e-m / infrared / IR (radiation emitted from block)
travels to worker OR is absorbed by worker OR travels without needing a medium
State the direction of the force that the N pole of magnet 2 exerts on the N pole of
magnet 1. justify
force (on N pole) is in direction of the (magnetic) field
how does and LDR work?
light dependant resistor,
as light intensity increases, resistance decreases, increase in current flow, decrease in voltage flow
what happens to the velocity of an object in short period of time as it accelerates downwards uniformly
velocity will increase in a constant rate
explain why direction of wavefronts change in way shown
(hits a boundary at an angle, angle of incidence= 45 and refracted= 33 wavelength decreases)
speed changes
wave speed is smaller at right hand side
lower section of wave slows down first
describe what is meant by direction of a magnetic field
direction of force on north plate, from north to south
what is meant by emf
energy supplied in driving charge in a circuit
energy supplied per unit charge
what is meant by background radiation
radiation which is always present, all around in our enviornment
how does a nuclear power station work
-advantages
-disadvantages
just like a power plant using fuels accept water gains thermal energy from nuclear reactions
-ad= No carbon dioxide or other greenhouse gases are produced.
Each kilogram of fuel contains an enormous amount of energy (it has a high energy density).
-dis= non renewable, radioactive waste produced, risk of nuclear accidents, expensive to build power plants and take a long time to do so
3 methods to produce electricity from water
tidal
wave
hydroelectric
explain hydroelectric electricity
-advantages
-disadvantages
building a dam wall in the river, holds water behind a wall, there is a huge height difference, relies on water rushing downstream through pipes through turbine blades which store ke and are used to power coil of wire in generator producing electricity
ad= electricity produced 24 hours
no co2 or greenhouse gas produced
renewable
dis= dam built floods large areas destroys habitats,
explain tidal electricity
-advantages
-disadvantages
same concept as hydroelectric but instead uses sea water
ad= renewable, no co2 or greenhouse gas produced, tides are easy to predict
dis= Only some places have big enough tidal changes to produce sufficient electricity in this way.
Tidal dams and machines can damage marine ecosystems and habitats.
explain wave electricity
-advantages
-disadvantages
uses the movement of waves up and down to drive turbines, and to produce electricity.
ad=renewable, enviornmentally friendly, sustainable
dis= do not much electricity, only work well on windy days when more waves are present.
explain two types of solar energy forms
solar panels- absorb infrared electromagnetic waves from the Sun to heat water for homes. little enviornmental impact, no production of co2, requires sun shine
solar cells-produce electricity directly from electromagnetic waves in sunlight. This can be transmitted through power lines to homes across the world, dependant on amount of sunlight, expensive, not efficient,
winds pros and cons
pros- renewable, no co2 production, easy and cheap to make turbines,
cons- look and sound unpleasant, needs lots of turbines thus large area, unpredicatable
geothermal explain
Cold water is fed through pipes underground and returns as steam due to the volcanic activity. The steam drives turbines to generate electricity.
Although it is renewable and environmentally friendly only a few counties in the world have geothermal energy.
what energy sources do not use sun as producer and what are their stores instead
geothermal- hot rocks underground tapping into internal energy stored in molten rocks deep in earth
nucelar- energy trapped inside atoms
tidal- motion of sea caused by gravity between moon and earth
where does the sun get its energy from
nuclear fusion
state form of energy stored in batteries
chemical
explain how earth wire protects user
if live wire touches metal case or insulation fails, current is directed towards earth through the earth wire
sun warms road, describe how energy from sun reaches earth and warms it
radiation from sun, electromagnetic/ visible/ infrared, travels through space, and is absorbed by the road, increasing its temperature
air above road is heated describe how this affects molecules of air
they gain ke move faster and move furhter apart
rays of light travelling towards a lens, describe what happens to light after it passes through the lens
light rays meet/ intersect
all light travels towards a point
point of convergence is focal point
state name given to a lens that produces a virtual image
magnifying lens
explain why an extreme high temp is needed when forcing nuclei of hydrogen-2 and hydrogen-3 together
high ke is needed
they repel each other
both are positively charged
explain how in a ac generator rotating coil continuosly causes galvonameter needle to show an alternating current
coil of wire cuts magnet field lines
induces an emf/ current
which is read/ shown in the galvonamter by its deflection
direction of current flow changes each 180 degrees rotation of coil
describe how a radiation used in smoke detectors ionise air
alpha
collides/hits with air particles
removing its electrons
why is alpha used instead of gamma for smoke detectors
gamma are more penetrating arent stopped by smoke particles like how alpha are because of low penetration
alpha is more ionising, ionises air more easily
explain what happens to motion of a trolley when angle of ramp increases
speed increases, a resultant force is acting on trolley
explain why high voltage is used to transmi t electrical power
heat loss depends on current, less energy lost to surrounding, weaker current is used due to high voltage, thinner wires can be used
explain how a relay works
iron core becomes a magnet
iron core attracts iron armature
armature pivot moves and contact touch
describe conduction
movement of thermal energy through a solid metal
due to its lattice/ particle vibration, transferring thermal energy/ charge to nieghbouring atom
free delocolsied electrons moving through the metal
transfer thermal energy when touching/ hitting other particles
thermal energy passes into water through base of pan, identify main method by which thermal energy is transferred throughout water
convection
what is meant by centre of gravity
place where all weight seems to act
explain why something has an unstable strcuture
small tilt causes its centre of gravity to no longer be verticley above its base
what is meant by electric field
region where an electric charge experiences a force
in a electric field force is in what direction
towards negative
explain why alpha particles are more ionising than beta
they have a bigger/stronger charge
and more kinetic energy
explain what happnes in core of a stable star
nucelar fusion
joining hydrogen nuclei into helium nuclei
hydrogen atoms become helium
state quantity used that astronomers use to determine speed at which galaxy is moving away
change in wavelength
state and explain use of optical fibres in medicine
description of fibre passing to site to be examined
light passes down fibre AND (image) returns (to sensor / observer)
extra detail, e.g. laser light source, illuminated organ, image, camera / type of sensor
state and explain why electrical sockets and plugs used outside need to be different from those used in room
can be wet, must be waterproof because water conducts electricity
radioactive tracers emit gamma rays can be used in medicine, their half life of the source of these gamma rays are 6 hours, explain why a source of gamma rays used in this way should not have half life shorter or longer than about 6 hours
longer- substance active in body for a long time
shorter half-life – might be insufficient time for investigation
explain why opening parachute doesnt reduce speed of skydiver to zero
no air resistance at 0 speed
still is a downward force caused by gravity
trolley moves and slowly slows down and stops explain in terms of work done energy change that takes place as trolley slows down
work done due to ke
ke decreases
thermal energy produced
explain in terms of molecules effect of increase in thermal energy on water
particles escape surface of water as water vapour
bonds are broken
molecules gain potential energy
explain in terms of molecules why a liquid expands more than a solid when heated
greater seperation with same increase in energy, weaker forces of attraction
internal energy of water decreases give a simple molecular account of this
molecules lose ke, internal energy depends on ke
define work done
force * distance moved in direction of force
why does an uncharged ball jump due to proximity of a negatively charged ball, resting on a metal table
electrons repelled to earth
ball positively charged
opposite charges attract
why does ball touch the rod and fall back into table, after being attracted
it is negatively charged by rod
and thus repelled
Energy change in a spring moving from stretched length to equilibrium
Elastic to gravitational
Explain why thinking distance is proportional to speed
Thinking distance is constant
Explain why braking distance is proportional to speed squared
Kinetic energy
Kinetic energy=1/2mvsquared
Word done=force/distance
Explain how evaporation cools person
Thermal energy from person to liquid
Molecules with most ke leva surface of skin
Molecules with low ke move slowest remain, they have less energy
If diameter of wire doubles what happens to reistancd
Divides by 4
Explain how transformer operates
Alternating voltage in primary circuit cute coils producing alternating magnetic field travels through iron core into secondary coil where an output induced alternating voltage is made
