GCSE Revision Physics

Radioactivity

unstable elements spontaneously emitting energetic particles by the decay of their atomic nuclei in order to become stable.

3 types of radiation

alpha - helium nucleus - 2 protons, 2 neutrons

beta - high speed electron

gamma - EM wave

Alpha particles

mass 4, charge 2+, most ionising, least penetrating, stopped by paper and smoke

Beta

stopped by aluminium, mass 1/2000 of a proton, charge -1

Gamma

uncharged, most penetratd ng, least ionising, stopped by lead

Alpha decay

loses 2 protons and neutrons, top number decrease by 4, bottom number reduce by 2, makes element + helium

beta decay

occurs when too many protons or neutrons, proton or neutron becomes electron, atomic mass stays same, atomic number increases by 1, makes new element and electron.

Gamma decay

just energy from nucleus, no change in numbers.

timeline of atomic model

john dalton - atoms can be created or destroyed

JJ Thomson - Plum pudding model

Ernest Rutherford - Nuclear model, alpha scattering

neils bohr - planetary - electron shells, electrons move between them

Activity

number of unstable atoms in that source that decays per second. measured in becquerel

half life

time it taes for NO of nuclei of isotope to halve

the time it takes for the count rate to decrease by half.

count rate (after) =

count rate/ 2^n

n = number of half lifes

Nuclear Fission

nuclear fission can be induced by bombarding 2 atoms with neutrons, the nuclie of the atoms decay split into 2, neutrons are released

how does fission release energy

kinetic energy of the products in fission are greater than that of the bombarding neutron and target atom

Nuclear Fussion

2 small nuclei are fused together to make 1 heavy nuclei and this proccess creates heat energy and used to create electricity

Nuclear power

Uranium fuel rods under going fussion, rods surrounded by moderator to increase likelyhood of being absorbed, this generates heat to produce steam, this used by turbine to generate electricity

irradiation

exposure to a radioactive source outside the body

Contamination

when radioative stuff is inside your body and can cause damage

millisievert

measure of radiation dose

gear

a wheel with teeth that transmits the rotational effect of a force

force x distance =

force x distance

Refraction is

when light waves change direction when they pass from one medium to another

Waves travel

at different speeds through different densities

Higher density =

slower wave

Reflection- Angle of incidence=

angle of reflection

3 primary colours of light

red blue green

Red + Blue =

Magenta

Red + Green =

Yellow

Blue + Green =

Cyan

Blue + Green + Red =

White

why does a white shirt look white

because it reflects all colors of light

why does a red shirt look red

because it reflects the red light and absorbs the green and blue light

why does a green shirt look green

Because it absorbs red and blue light and reflects green light

why does a black blazer look black

because it absorbs all light

the 2 types of wave

Transverse, longitudinal

Examples of transverse waves include

Light waves, radio waves

Examples of longitudinal waves include

Sound waves, seismic P waves

the wave equation

Wave speed = frequency X wavelength

Frequency

How many whole waves in a second

Amplitude

is the distance from the centre line (or the still position) to the top of a crest or to the bottom of a trough .

Wavelength

The wavelength of a wave is the distance between two waves

A light wave bend towards the normal when

less dense to more dense

a light wave bends away from the normal when

more dense to less dense

magnification =

image height

object height

Types of energy stores

thermal kinetic nuclear chemical gravitational elastic electrostatic magnetic

energy transferes are

mechanisms which allow energy to be moved from one location to another

Weight =

mass X gravity

Mass

is a measure of how much of an object there is and how mard is it to accelerate

Force

mg

GPE

mgh

work =

force X distance

Kinetic energy

½ mv²

Hookes law

The extension of a spring is directly proportional through the origin to the force applied, provided irs limit of proportionality is not exceeded

Hookes law equation

F = K X e

K=spring constant in N/m

Power =

work/time

Power also equals

Energy transfered/time

efficency =

useful power/total power input

When a current floes through a wire

a magnetic field is created around it

aNticlockwise

North

clockwise

south

LEFT hand grip rule

Thumb-Force , second-field, third-current

The motor effect

when a current flows through a magnetic field it will experience a force and it will move

Why do we get movement WITH THE MOTOR EFFECT

A CURRENT CARRYING WIRE WILL HAVE A MAGNETIC FEILD AROUD IT. THIS FEILD WILL INTERACT WITH THE MAGNETS AND BE PUSHED OUT OF THE FEILLD

The biggest effect will be when

the current and field are at right angled to each other

If the current and field are parallel there will be

no force

The electric bell

the current flows from the electromagnet because there is a complete circuit. This causes the iron core to become magnet and it attracts the soft iron armature this makes the hammer hit the gong.

The motor effect 3

A wire carrying a current creates a magnetic field . This can interact with another magnetic field, causing a force that pushes the wire at right angles.

An electro magnet

An electro magnet is a temporary magnet made by winding wire around an iron core.

Charge=

current x time

like charges

Different charges

REPEL

ATTRACT

Radial field

As you move away from the sphere the feild gets weaker

negitive sphere, - out + in

plus sphere, -in +out

Charge is measured in

Coulombs

Current is the

measure of the movement of charge and is measured in amps (coulombs per second)

Ametre

measures how much charge is moving around a current

Voltmetre

measure of p.d this is the measure of energy a cells gives to the charge§

Resistor

Resistance is a measure of hoe hard it is for current to flow through a component , measured in ohms.

V=

IR

IV Graph filament bulb

Diode

Light dependant resistor

As the light intensity increases the resistance falls

IV experiment

Variable resistor, bulb, ammeter in series, voltmeter in parallel

Change current and measure the P.d

Thermosistors

As temprature increases resistance falls

Ohmic resistor

LED graph

Series more bulbs=

more resistance

Parallel more bulbs =

more current and less resistance

Resistance in series and NO. of bulbs

Graph goes up

Not straight because bulbs are less bright and cold.

Resistance in parallel and NO. of bulbs

Series

resisatance can be added, current same everywhere, potential differences add to supply.

Parallel

Potential difference = same for all resistors, total current = all current added together.

Parallel Rtotal =

V/I total.

Using a LDR to measure light intensity

V =

E/Q

Energy transfered =

Charge x P.D

P=

E/T

I=

Q/T

Power =

I² x R

density =

mass/ volume

Density Eureka Can experiment

use balace to measure mass, submerge object into eureka can with water in it with a measuring cylinder underneath the spout, record the volume of water in the cylinder, work out density with d=m/v formula