paper 1 physics Flashcards
what direction do electrons flow in
Opposite direction of the conventional current
Why do electrical charges move through metals?
They have some electrons that are free to move from their atoms
What happens when electrical current flows through a resistor?
Electrical energy is transformed into heat energy
In a series circuit
- same current
- the total potential difference is shared between the components
- total resistance of components is sum of the resistance of each component
In a parallel circuit…
the total current through the whole circuit is the sum of the currents through the separate components
• the p.d. across each branch is the same
why adding resistors in series increases
the total resistance
lowers current
only one path for current to flow
any added resistance reduces the current flow
why adding resistors in parallel
decreases the total resistance
both resistors have the same p.d.
current increased
the total resistance decreased
force used is the same as the p.d.
adding a resistor creates another direction to go in
describe the current in a series circuit
the current is the same at all positions
as charge only has one path to flow
describe the current in a parallel circuit
current shared between different branches
when the charge reaches a junction it splits
what is the definition of power (2)
the rate energy is transferred
the rate work is done
two equations for power
energy transferred/ time
work done/ time
unit of power
watt W
Two motors lift the same mass through the same height. Motor A does this in half the time of motor B. Which dissipates the most power?
Motor A
Energy transferred is the same but the time taken is less
Two equations for power of a circuit
current (amperes)* potential difference (volts)
I*V
current(2)×resistance (ohmns)
= I(2)R
equation linking energy transferred, power and time
E= P*t
equation linking energy transferred charge (power) and potential difference
E= Q*V Q= charge, coulombs V= potential difference, volts
what 3 things determine the power of a circuit device
- potential difference across circuit
- the current through the circuit
- the amount of energy transferred in a given time
what is insulation
-reducing the rate of energy transfers by heating
ways of reducing unwanted
energy transfers
-reducing waste output
lubrication,thermal insulation
-recycling waste output
recycling thermal waste energy as input energy
three methods of reducing heat loss in buildings
double glazing, prevent energy transfer by conduction in windows
- lot and wall insulation, prevents convection currents being created
- thicker walls
practical investigating effectiveness of different insulators practical
- boil water in kettle, pour in a sealable container (beaker and lid)
- measure the mass of water in container
- uses thermometer to measure initial temp of water
- seal container for 5 mins, measure with stop watch
- remove lid, measure final temp of water
- pour away water and let container cool to room temp
- repeat experiment but wrap container in different material (foil, paper)
- seal and use same mass of water each time
Kinetic energy equation
kinetic energy = 0.5 × mass × speed 2
Ek = 1/2 * m *v2
kinetic energy, Ek , in joules, J mass, m, in kilograms, kg speed, v, in metres per second, m/s
energy transfers in a battery powered motor
battery coverts chemical energy into electrical energy
motor converts electric energy into kinetic energy
waste energy in the form of heat due to friction
Equation for gravitational potential energy
GPE=mgh
gpe= mass × gravitational field strength × height
Ep, in joules, J
mass, m, in kilograms, kg gravitational field strength, g, N/kg may be given)
height, h, in metres, m
energy transfers for a bungee jumper
when falling GPE converted to KE of the jumper
cord tightens, KE converted and stored as ElasticPE
at lowest point the jumpers initial GPE equals the EPE stored in the cord
explain why a bunjee jumper slows down once cord begins to stretch
kinetic energy decreases as converted to EPE
KE proportional to V(2) as KE decreases the velocity decreases as well
Efficiency formula
useful output / total input
ways to increase the efficiency of an intended energy transfer (mechanical machine, radiator, water pan)
machine- lubricate any moving parts, reduce friction, reduce energy loss by heating
radiator, metal foil sheets behind radiator reflect heat back into room not absorbed by wall
placing lid on pan to reduce heat loss from top
What is a half-life?
time taken for half the nuclei in a sample to decay
how half-life are related to the random nature of radioactive decay.
- cannot be predicted (random) when any one nucleus will decay,
- if the half-life is a constant the activity of a very large number of nuclei can be predicted during the decay
what is the half life if 80 atoms falls to 20 over 10mins,
80/2 = 40
40/2 = 20
so two half lives in 10mins
So half-life is 5mins
properties of a alpha particle
- two protons and neutrons
- same as a helium nucleus
- 2-10 cm in air
properties of beta radiation
charge of -1 proton
stopped by aluminium
several metres of air
properties of gamma radiation
electromagnetic wave
stopped by lead and concrete
mass and charge remain unchanged
moist ionizing and least ionizing radiation
most = alpha least = gamma
what is the equation for net decline
final activity of half life/ initial activity of half life
*100
what is electric current
flow of electrical charge
-connected to a cell in a complete circuit Amps (A)
equation linking charge, current and time
Q= I*t
Q=charge, coulombs
I= current, amperes
t= time, seconds
two factors does the current in a circuit depend on
potential difference
resistance
4 components where resistance is not constant as current changes
- lamps
- diodes
- thermistors
- light dependent resistors,LDR
what is different about current flow in diode
- flows in one direction
- resistance very high, in the other direction preventing current flow
investigating factors that affect resistance , practical
crocodile clip
- set up circuit
- attach crocodile clip to the wire, level at 0cm on ruler
- attach second crocodile clip 10 cm away in increments
- close switch, measure voltage and current each time
- calculate resistance for each length using R=V/I
what is internal energy
the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system.
state the consequence for energy transfer of a material with high thermal conductivity
The higher the thermal conductivity of a material the higher the rate
of energy transfer by conduction across the material.
what is the equation for specific heat capacity
= mass × specific heat capacity
× temperature change
what is specific latent heat
the amount of energy
required to change the state of one kilogram of the substance with
no change in temperature.
equation for SLH
E = m * L
energy for a change of state = mass × specific latent heat
what is the Specific latent heat of fusion
Specific latent heat of vaporisation
fusion – change of state from solid to liquid
vaporisation– change of state from liquid to
vapour
what do flat spots show on a change of state graph
flat spots show enrgy transfer e.g. melting, condensing
this is not used to change temperature
practical for investigating SHC
- have a block of solid material for heater and thermometer
- measure mass of block
- wrap bock in an insulating layer, insert thermometer and immersion heater
- connect joule meter to immersion heater
- measure initial temperature and set p.d. to 10 V
- start stop watch and power supply
- as block heats use thermometer and measure temperature every minute
-do calculation for shc
or rearrange shc equation
E=Pt, P=VI
what is a random error
random= unpredictable differences
reduced by making more measurements,a mean value
what is a zero error
zero=equipment that isn’t zeroed properly
what is a systematic error
systematic error= wrong by the same amount every time, measure correctly
what is validity
where results are both repeatable and reproducible
answer the original question
repeat= same, same results
produce= someone else, similar results
what is electrostatic electricity
when two insulators are rubbed together
electrons are passed from one to another
what happens when an insulator gains or loses electrons (static electricity)
gains electrons= negatively charged
loses electrons= positively charged
what is produced by movement of electrons
positive and negative electrostatic charges
positive static charge caused by electrons moving away
causing materials to lose some negative charge, then is left with equal positive charge
what is density
tells you the mass for a given volume
density equation
p= m/V
density in kg/m3
volume in m3
mass in kg
1g/cm3= 1000kg/m3
describe density of solids and liquids
s and l high as particles packed close together a lot of mass for their volume
gas low density spread out
why polystyrene has a low density
it has a very open structure
full of air spaces
small mass for its volume
how to find the density of a regular solid object
- use a balance to measure its mass
- measure the volume using a ruler cube = lwh
how to find the density of a irregular solid , vase
- use a balance to measure its mass
- find volume by submerging it in a eureka can filled with water
- by displacement the water will be transferred to the measuring cylinder
- volume displaces= volume of object
- then mass/volume
density of a liquid
-measuring cylinder on balance and zero balance
-pour 10ml liquid into measuring cylinder and record mass
-another 10ml mcylinder record total volume and mass
repeat until mcylinder full
-each measurement use formula to find density
-take average of calculated densities
