Physics igcse edexcel all

D/t graph

gradient = velocity

horizontal line = stationary

distance 0 = back at starting point

curved line = acceleration

v/t graph

area under the line is the distance travelled

Newton's First Law

object has a constant velocity unless acted on by a resultant force

newtons second law

f=ma

Newton's Third Law

every force has an equal and opposite reaction force

terminal velocity

no air resistance at first, only weight

as it falls it accelerates and increases in speed

acceleration decreases as drag increases

a = d, no resultant force

no acceleration, terminal velocity reached

thinking distance

distance travelled in the time between realising you need to brake and actually pressing the breaks

factors affecting thinking distance

greater speed

slower reaction time due to alcohol or tiredness

braking distance

time between pressing the brakes and the vehicle coming to a stop

factors affecting braking distance

greater speed or mass

poor road conditions

stopping distance

thinking distance + braking distance

deformation

when an object does not return to its original shape when the load has been removed

hookes law

F = kx

Force is directly proportional to extension until the limit of proportionality

Moments

anticlockwise moment = clockwise moment (equilibrium)

moment = force * perp distance from pivot

momentum

p = mv (kgm/s)

safety features in cars

increases time taken to come to rest

as time increases, force decreases, due to f = change in momentum / time

ie by stretching

conservation of momentum

total momentum before = total momentum after

in a collision

current

measured in Amps

Rate of flow of charge / electrons

measured with an ammeter in series

conserved at a junction

conventional current

rate of flow of positive charge

opposite direction to electron flow as electrons as negative

potential difference

measured in volts

work done per unit charge between 2 points

voltmeter placed in parallel

resistance

measured in ohms

greater the resistance, harder for current to flow

resistor / ohmic conductor

current directly proportional to voltage

filament lamp

resistance changes as voltage and current change as current increases through filament, so does temperature, increasing collisions and resistance

Thermistor

Resistance decreases as the temperature increases

Used in thermostats

LDR

resistance decreases as light intensity increases

series circuits

same current flows through every component

total resistance = R1 + R2...

voltage is shared

parallel circuits

seperate branches

current is shared between each branch (charge only flows one way)

voltage is same across every branch

dangers of electricity

damaged insulation - fire hazard

overheating of cables - melts insulation

damp conditions - electric shock (water conducts)

fuse

thin piece of wire that overheats and melts if current too high, protecting the circuit. current rating is higher than current in circuit.

circuit breakers

automatic electromagnet switch which breaks the circuit if current rises over a certain value, can be reset and operate faster than fuses

earthing

creates a safe route for current to flow through in case of a short circuit, low resistance so a strong current surges through and breaks fuse to disconnect appliance

double insulation

plastic casings covering electrical components

direct current

1 direction

alternating current

continuously changes direction

longitudinal waves

waves where oscillations are parallel to direction of energy transfer

cannot move in a vacuum

compressions - close together

rarefractions - spaced apart

transverse waves

waves that vibrate perpendicular to direction of energy transfer

amplitude

distance from undisturbed position to the peak or trough of a wave

wavelength

distance from one point on wave to the same point on the next wave in metres

frequency

number of waves passing a second in hertz

time period

time taken for a single wave to pass a point in seconds

wavefront

space between = wavelength

doppler effect

apparent change in wavelength and frequency of wave emitted by a moving source, speed stays constant so wavelength/frequency must increase/decrease

electromagnetic waves

transverse waves that transfer energy from the source of the waves to an absorber

all can go through vacuum at same speed

EM spectrum

radio

micro

infra

visible light

ultraviolet

xrays

gamma

high frequency = high radiation

can be reflected and refracted

visible light spectrum

red = longest wavelength (lowest frequency)

violet = shortest wavelength (highest frequency)

applications of radiowaves

communication (radio and TV)

can be reflected from atmosphere

applications of microwaves

communication

heating food

can penetrate earth's atmosphere

applications of infrared

thermal imaging

night vision

fibre optic communication

undergo TIR

applications of visible light

fibre optic communication

photos/videos

cameras are setup to detect visible light

applications of ultraviolet

fluorescent lamps

it fluoresces with ultraviolet lighting

applications of xrays

x-ray images

x-rays can penetrate soft tissue but not bone

applications of gamma

sterilising medical instruments

treating cancer

gamma kills bacteria

dangers of microwaves

heat damage to internal organs

microwaves emit very large amounts of energy

dangers of infrared

skin burns

to protect, wear gloves

dangers of visible light

bright light can cause eye damage

dangers of ultraviolet

sunburn

eye damage

ionising - kills cells / causes malfunction - resulting in premature aging - and diseases

sunscreen absorbs UV

dangers of xrays and gamma

kills cells

mutations

cancer

ionising - penetrates body - causes gene mutation

minimise exposure / lead apron

reflection

wave hits boundary between two media and doesnt pass through, instead staying in medium, resulting in a change of direction

law of reflection

angle of incidence (approaching boundary) = angle of reflection

less dense to more dense

light will bend towards the normal

PRAC : investigating refraction

draw around perspex block

direct beam of light at side of block

mark where the ray enters and exits the block, as well as a point on the ray entering and exiting the block (ie next to ray box)

join points

repeat for different angles

PRAC: investigating refraction issues

error with 90 not being correct (use set square)

inaccurately marked (sharp pencil)

PRAC : investigating snell's law

draw around glass block

draw norma;

measure angles of incidence and mark on paper

direct beam of light at side face of block

mark point close to ray box, entering and exit points, and exit light ray 5cm away

join dots

repeat for different angles

TIR occurs when

i > c and incident material is denser than second material

TIR is useful because

reflects light along optical fibres - ie for communications and endoscopes, TIR each time it hits each of fibre

Prisms are useful because

periscopes, binoculars, telescopes, cameras, light is TIR

meaning of critical angle

when angle of refraction = 90, light is reflected along boundary, so angle of incidence = c

conservation of energy

energy cannot be created or destroyed, it can only be transferred from one store to another

conduction

solids

metals are good conductors

non metals are poor conductors (good insulators)

delocalised electrons can collide with atoms - transferring vibrations and energy

convection

liquids and gases

fluid expands and is less dense

hot fluid rises

hot fluid cools and sinks back down

forming a convection current

thermal radiation

hotter objects emit more infrared radiation

black best at emitting and absorbing IR

white and shiny worst at emitting and absorbing IR

PRAC : conduction

attach ball bearings with wax to ends of 4 different metal strips hanging over a heat source

heat middle of strips

heat will be conducted along to the ball bearing which will drop as wax melts

time each ball dropping for the 4 balls

repeat

PRAC : investigate convection

fill beaker with cold water and place potassium permanganate crystals

heat with BB

repeat with hot water

dissolved purple follows convection current faster in hot water

PRAC : radiation

setup four flasks; black, grey, white, silver

fill with hot water

note starting temp, measure temps every 30s for 10m

reducing conduction

use materials with low thermal conductivity - insulators

use fibreglass - air trapped between fibres - prevents convection, air is a poor conductor

reducing convection

reduce formation convection currents - prevent movement

GPE =

KE

so you can use the KE and GPE formulae to find speed or mass

power

rate of energy transfer / work done

pressure in a fluid (liquid or gas)

force exerted evenly in all directions

pressure creates forces

forces act at right angles to surface

kinetic theory of gases

molecules in a gas are in constant random motion at high speed

no specific path = sudden changes in motion due to collision

BROWNIAN MOTION

gas and pressure contianer

gases fill their container

they collide with containers

producing a net force perpendicular to surface

high pressure = more collisions at greater force

compressed - more frequent collisions - higher net force - higher pressure

absolute zero

-273 C

particles have no net movement - zero kinetic energy

kelvin scale

0K = -273C

proportional to avg kinetic energy

increase in temperature

hotter the gas, faster the movement due to having more KE, so more frequent collisions

law of magnetism

like repel

unlike attract

this is non contact force

magnetic materials

magnetically soft (iron) - easy to magnetise and lose magnetism

magnetically hard (steel) - difficult to magnetise, permanently magnetised

magnetic field :

region around a magnet where a force acts on another magnetic material

magnetic field lines

show strength and direction of a field - spacing (strength - closer the stronger)

magnetic field around bar magnet

strongest at the poles - weaker as distance from magnet increases

ALWAYS from north to south

magnetic material examples

iron, cobalt, nickel

types of magnet

permanent - made from permanent magnetic materials ie steel, producing own magnetic field

induced - temporarily magnetised in magnetic field

PRAC : investigate mag field for permanent bar magnet

draw a dot at one end of magnet and place compass next to dot

draw new dot where compass points

repeat until connecting to other end of magnet

current in conducting wire

produces a magnetic field around the wire

no current = no mag field

more current = stronger mag field

right hand thumb rule

thumb - direction of current

other fingers - direction of field

motor effect

a wire with current flowing through it is placed in a magnetic field and experiences a force

producing two interacting magnetic fields (around wire, one wire is placed into)

wire will experience a force

motor effect - dc motor

coil of wire in uniform magnetic field

current flowing through coil produces magnetic field

force exerted on wire from interaction of two magnetic fields

forces act in opposite directions on each side of coil, rotation

after 90 degrees, split ring no longer in contact with brushes - no current flows through coil - no forces act

motor effect loudspeaker

coil of wire around one pole of perm magnet

AC current through coil - current constantly changing direction = direction of field too

interaction of two mag fields

exerting a force on coil

coil oscillates as force constantly changes direction

coil causes speaker to oscillate - air oscillates - creating sound waves

flemings left hand rule

First - mag Field

seCond - Current

THumb - THrust (force)

how is voltage induced in a conductor

when it moves through a magnetic field or when a magnetic field changes through it

generator effect

factors affecting induced potential difference

speed at wire/coil/magnet moved - increases rate mag field lines cut, increases induced pot diff

number of turns - increase induced pot diff as each coil cuts through mag field lines

size of coils - increase area increases pot diff, more wire to cut through

strength of mag fields - increase pot diff induced