Aqa Gcse P2 Revision Notes

Front 1

Forces act in

Back 1

Forced act in pairs.

Front 2

When a force acts in one direction

Back 2

an equal and opposite force is exerted in other direction

Front 3

what is a reaction force?

Back 3

When 2 forces interact they are equal and opposite in direction e.g. a person exerts a force on the chair but the chair applies an equal force upwards on the person, a reaction force.

Front 4

Weight is a

Back 4

force measured in newtons.

Front 5

weight and mass

Back 5

Don’t confuse mass and weight as mass is actually the amount of ‘stuff’ that makes up an object measured in kilograms.

Front 6

The equation to work out weight is...

Back 6

Weight is the force calculated by Weight (N) = Mass (kg) x Gravitational field strength (N/kg)

Front 7

The gravitational field strength of earth is

Back 7

The gravitational field strength on Earth is taken as 10N/kg.

Front 8

The speed of an object is

Back 8

distance travelled in seconds

Front 9

The gradient of a line on a distance time graph represents

Back 9

speed

Front 10

On a distance time graph, the greater the gradient of line

Back 10

the greater the speed

Front 11

On a distance time graph if the line is horizontal

Back 11

the object is stationary

Front 12

On a distance time graph, if the object is moving at a constant speed the line is

Back 12

a straight line sloping upwards

Front 13

How do we calculate the speed of an object?

Back 13

speed (m/s)= distance traveled (m)

-------------------------------

Time taken in (s)

Front 14

Velocity is

Back 14

speed in a given direction

Front 15

If an object changes direction...

Back 15

it changes velocity even if the speed remains the same

Front 16

Therefore if the velocity of an object changes

Back 16

it accelerates

Front 17

Acceleration=

Back 17

a (m/s2)= v-u

-------

t

where v is the final velocity, u is the initial velocity and t is the time

Front 18

The gradient of the line on a velocity time graph represents

Back 18

acceleration

Front 19

The steeper the gradient of a velocity time graph

Back 19

the greater the speed

Front 20

if the line on a velocity time graph is horizontal the object is

Back 20

travelling at a steady speed so the acceleration is zero

Front 21

The distance travelled by an object is given by

Back 21

the area under the line of its velocity time graph

Front 22

What is the resultant force?

Back 22

single force that would have the same effect on the object as all the original forces acting together.

Front 23

When the resultant force of an object is zero...

Back 23

if object is at rest it will stay at rest

if the object is moving it will carry on moving at the same speed in the same direction

Front 24

when the resultant force of an object is not zero,

Back 24

there will be acceleration in the direction of the force

Front 25

if the resultant force is not zero the object will,

Back 25

accelerate in the direction of the resultant force if it was at rest

if object is moving in same direction of resultant force it will accelerate in that direction

if object is moving in opposite direction of resultant force it will decelerate

Front 26

A resultant force always causes an

Back 26

acceleration

Front 27

Acceleration is the change in velocity

Back 27

an object can accelerate by changing =its direction even if it is going at a constant speed. so a resultant force is needed to make the object change direction

Front 28

resultant force is found by

Back 28

f=m x a

f= force (N)

m= mass(kg)

a=acceleration (m/s2)

Front 29

What is the stopping distance?

Back 29

the distance traveled during the drivers reaction time plus the distance it travels under the braking force

Stopping distance = thinking distance + braking distance

Front 30

thinking distance is increased

Back 30

if driver is tired or under influence of drugs or alcohol

Front 31

Balanced forces occur when

Back 31

an object is stationary or moving at a constant speed. The faster an object is moving the bigger the frictional forces acting on it.

Front 32

Braking distance can be increased by

Back 32

poorly maintained roads or bad weather conditions

condition of car i.e if the brakes or tyres of car are worn

Front 33

An object falling through a fluid or gas will initially accelerate due to the force of gravity as

Back 33

there is a resultant force acting on it which is gravity

Front 34

The force of gravity can be referred to as

Back 34

weight

Front 35

to work out the weight you do

Back 35

w= m x g

where w is the weight (N) as it is the force

m is the mass (kg)

g is the acceleration due to gravity (m/s2)

Front 36

When an object falls through a fluid,

Back 36

the fluid exerts a drag force on the object

resisting its motion

Front 37

in a fluid, the faster the object falls

Back 37

the bigger the drag force becomes until eventually it will equal the weight of the object.

resultant force is now zero so the body stops accelerating. It moves at a constant speed called Terminal velocity

Front 38

What is terminal velocity?

Back 38

The constant speed that a freely falling object eventually reaches when the resistance of the medium through which it is falling prevents further acceleration.

Front 39

what is the extension?

Back 39

the increase in the length from the original of the spring

Front 40

If an object is elastic, how does it behave?

Back 40

an object that regains its original shape when the forces deforming it are removed

Front 41

the extension is directly proportional to

Back 41

the force applied

Front 42

If we apply too big of a force,

Back 42

the line begins to curve because have exceeded the Limit Of Proportionality

Front 43

Hookes law

Back 43

that the extension is directly proportional to the force applied provided the limit of proportionality is not exceeded.

Front 44

Hookes law equation is

Back 44

f=k x e

f= force (N)

k= the spring constant of spring in (N/m)

e= extension (m)

Front 45

the stiffer the spring

Back 45

the greater its spring constant

Front 46

when an elastic object is stretched

Back 46

work is done. this is stored as elastic potential energy in the object

Front 47

when the stretching force is removed

Back 47

this stored energy is released

Front 48

Whenever an object starts to move

Back 48

a force must have been applied to it

Front 49

when a force moves an object

Back 49

energy is transferred and work is done

Front 50

Work done is equal to

Back 50

the energy transferred

Front 51

work done is calculated using

Back 51

w=f x d

w= work done (J)

f= force (N)

d= distance (m)

Front 52

what is gravitational energy

Back 52

energy stored in an object because of its position in the Earths gravitational field strength

Front 53

When an object is moved vertically upwards,

Back 53

it gains gravitational potential energy equal to the work done on it by the lifting force

Front 54

change in gravitational potential energy is calculated using

Back 54

Ep = m x g x h

Ep is change in gravitational potential energy (J)

m is the mass (kg)

g is the gravitational field strength (N/kg)

h is height (m)

Front 55

Power is... and can be calculated using...

Back 55

power is the rate of energy transferred

p= e

-----

t

p is power (W)

e is energy (J)

t is time (s)

Front 56

All moving objects have

Back 56

kinetic energy

Front 57

the greater the mass of an object, the greater the speed and

Back 57

the more kinetic energy it has

Front 58

kinetic energy equation

Back 58

Ek= 1/2 x m x v2

Ek is kinetic energy (J)

m is mass (kg)

v is speed (m/s)

Front 59

Summary of elastic potential energy

Back 59

if object regains shape after being stretched or squashed it is described as elastic

work is done on object to stretch or squash it, so the energy transferred to it is elastic potential energy energy.

when object returns to its original shape, this energy is released

Front 60

The greater the mass of object, the greater the speed and greater its

Back 60

momentum

Front 61

Momentum is calculated doing

Back 61

p=m x v

p= momentum in (kg m/s)

m= mass (kg)

v=velocity (m/s)

Front 62

whenever an object interacts

Back 62

the total momentum before is equal to the total momentum afterwards provided no external forces act on them

Front 63

What is the conservation of momentum?

Back 63

the total momentum before the interaction is equal to total momentum after

Front 64

if one side of the momentum calculation is positive

Back 64

the other side is negative

Front 65

When two objects are at rest

Back 65

their momentum is at zero

Front 66

when a force acts upon an object that is moving or is able to move

Back 66

the momentum changes

Front 67

If the impact time is short

Back 67

the forces acting on the object are large.

As the impact time increasing the force becomes less

Front 68

When two vehicles collide

Back 68

the both exert equal and opposite forces on eachother and their total momentum is unchanged

Front 69

When two electrically insulating objects are rubbed together

Back 69

electrons are rubbed off one material and deposited on the other

Front 70

Because the electrons have an negative charge

Back 70

the material that gains the electrons becomes negatively charged, so the one that loses them becomes positively charged.

This is called charging by friction

Front 71

a diode

Back 71

allows current through it in one direction

Front 72

light emitting diode

Back 72

emits light when current passes through it

Front 73

a fixed resistor

Back 73

limits current in circuit

Front 74

variable resistor

Back 74

allows the current to be varied

Front 75

a fuse

Back 75

designed to melt and therefore break the circuit if the current through it is greater than a certain amount

Front 76

LDRs

Back 76

LDRs (light-dependent resistors) are used to detect light levels, for example, in automatic security lights. Their resistance decreases as the light intensity increases:In the dark and at low light levels, the resistance of an LDR is high, and little current can flow through it.In bright light, the resistance of an LDR is low, and more current can flow through it.

Front 77

thermistor

Back 77

Thermistors are used as temperature sensors, for example, in fire alarms. Their resistance decreases as the temperature increases. At low temperatures, the resistance of a thermistor is high, and little current can flow through them.At high temperatures, the resistance of a thermistor is low, and more current can flow through them.

Front 78

potential difference =

Back 78

v= W

-----

Q

v is p.d (v)

w is work done (J)

Q is charge (C)

Front 79

Resistance is the opposition

Back 79

to current flow

Front 80

resistance is calculated using

Back 80

R= V

----

i

where r is the resistance (in ohms)

v is p.d (v)

i is current (A)

Front 81

Ohms law

Back 81

the current is directly proportional to the potential difference across the resistor.

Front 82

Any component that obeys ohms law is called an

Back 82

Ohmic conductor

Front 83

on a current potential difference graph for a filament bulb

Back 83

the line is a curve so current is not directly proportional to the p.d.

resistance of filament bulb increases as current increases. this is because the resistance increases as the temp increases

Front 84

in a series circuit, the components are connected one after another so

Back 84

if there is a break in the circuit anywhere , charge stops flowing

Front 85

current is

Back 85

I= V

---

R

Front 86

the bigger the resistance of a component

Back 86

the bigger its share of the supply p.d

Front 87

in a parallel circuit

Back 87

each component is connected across the supply so if there is a break in one part of circuit charge can still flow in other parts

Front 88

each component is connected across the p.d supply so

Back 88

p.d across all components is the same

Front 89

the bigger the resistance of the component

Back 89

the smaller the current through it

Front 90

Frequency of the UK mains supply is

Back 90

50Hz which means it changes direction 50 times each second

Front 91

therefore the voltage of UK mains supply is

Back 91

230 volts

Front 92

the frequency of an a.c supply can be determined from an oscilloscope trace using equation

Back 92

f= 1

---

t

f is frequency (Hz)

t is time taken for one cycle (s)

Front 93

why is the outer cover of a three pin plug made of plastic or rubber?

Back 93

because both these materials are good electrical insulators

Front 94

the pins of the plug are made of brass as

Back 94

brass is a good electrical conductor as it is hard and will not rust or oxidise

Front 95

the brown wire is

Back 95

the live wire

Front 96

the blue wire in the

Back 96

neutral wire

Front 97

the yellow and green wire is

Back 97

the earth wire

Front 98

appliances with metal cases must be

Back 98

earthed

Front 99

appliances with plastic cases do not need to be earthed because

Back 99

they are said to be double insulated

Front 100

in a cable, the more current to be carried

Back 100

the thicker the cable

Front 101

why do appliances with metal cases need to be earthed?

Back 101

because if a fault develops and the live wire touches the metal cause, the case becomes live and could give and electric shock to anyone who touches it

Front 102

the rating of the fuse should be slightly higher than the normal working current of the appliance because

Back 102

if it is much higher, it will not melt soon enough to break the circuit and if it is not higher than the normal current it will melt as soon as the appliance is switched on

Front 103

what is a circuit breaker?

Back 103

an electromagnet switch that opens and cuts off the supply if the current is bigger than a certain value

Front 104

what is a RCCB? (residual current circuit breaker)

Back 104

cuts of the current in the live wire if it is different to the current in the neutral wire.

it works faster than a fuse or ordinary circuit breaker

Front 105

when a charge flows through an appliance, electrical energy is transferred to other forms. in a resistor

Back 105

electrical energy is transferred to the resistor so the resistor becomes hotter

Front 106

the nuclei of a radioactive substance is

Back 106

unstable

Front 107

how does the nuclei of a radioactive substance become stable?

Back 107

Radioactive Decay

Front 108

Name the three types of radiation emitted

Back 108

alpha, beta , gamma

Front 109

Background radiation is

Back 109

around us all the time. it is from radioactive substances in environment, from space, and devices like x rays

Front 110

Rutherford, Geiger and Marsden devised an

Back 110

alpha particle scattering experiment, in which they fired alpha particles at thin gold foil

Front 111

What did they discover in Rutherfords experiment

Back 111

most of the alpha particles passed straight through the foil, this means that most of the atom is just empty space.

some of the alpha particles were deflected through small angles which suggests that the nucleus has a positive charge.

a few rebound through very large angles. this suggests that the nucleus has a large mass and a very large positive charge

Front 112

What happens in alpha decay

Back 112

the nucleus loses 2 protons and 2 neutrons

Front 113

What happens in beta decay?

Back 113

a neutron in the nucleus changes into a proton and an electron

Front 114

an isotope is

Back 114

same element with different number of neutrons in nucleus

Front 115

Atomic number

Back 115

number of protons in atom

Front 116

Mass number

Back 116

protons plus neutrons

Front 117

Beta is a

Back 117

high speed electron from nucleus, emitted when neutron in nucleus changes to a proton and electron.

0

Represented as B

-1

Front 118

Gamma ray is

Back 118

electromagnetic wave released from nucleus with no overall charge

Front 119

Alpha is

Back 119

made up of two protons and two neutrons

when a nucleus emits alpha particle the atomic number goes down by two and the mass number goes down by four

Front 120

What is ionisation?

Back 120

when nuclear radiation travels through a material it will collide with the atoms of a material and knock the electrons off creating ions

Front 121

Alpha particles properties

Back 121

relatively large so have lots of collisions with atoms, they are strongly ionising.

they can be stopped by thin sheet of paper human skin or few cm of air

alpha particles have positive charge so are deflected by electric and magnetic fields

Very ionising as once in body can not escape out

Front 122

beta particle properties

Back 122

much smaller and fast than alpha so less ionising and penetrate further

blocked by few metres of air or thin sheet of aluminium

negative charge and are deflected by electric and magnetic fields in opposite direction to alpha particles

Front 123

Gamma particle properties

Back 123

electromagnetic waves so will travel long way through material before colliding with atom

weakly ionising

very penetrating

stopped by several cm of lead or several metres of concrete

not deflected by magnetic or electric fields

Front 124

What is the half life of a radioactive isotope?

Back 124

the average time it takes for the number of nuclei of the isotope in a sample to halve

Front 125

the activity of a radioactive source is

Back 125

number of nuclei that decay per second

Front 126

number of atoms of radioactive isotope and activity

Back 126

both decrease by half every half life

Front 127

Alpha sources are used in

Back 127

smoke alarms

Front 128

beta sources used for

Back 128

thickness monitoring

Front 129

gamma and beta sources used as

Back 129

traces in medicine. it is swallowed or injected and its progress around the body is monitored by a detector outside the patient

Front 130

radioactive dating is used for

Back 130

finding the age of ancient material.

carbon dating used to find age of wood and other organic material

uranium dating used to find age of igneous rocks

Front 131

nuclear fission is the

Back 131

splitting of atoms nucleus

Front 132

what two fissionable isotopes are commonly used in a nuclear reactor?

Back 132

uranium-235 and plutonium-239

uranium 235 is most commonly used

Front 133

Nuclear fission process

Back 133

for fission to occur the uranium 235 or plutonium 239 nucleus must absorb a neutron.

the nucleus then splits into two smaller nuclei.

in this process two or three more neutrons are emitted and energy is released. the energy released in such a nuclear process is much greater than the energy released in a chemical process such as burning

Front 134

When does a chain reaction occur?

Back 134

A chain reaction occurs when each fission event causes further fission events. In a nuclear reactor the process is controlled so one fission neutron per fission on average goes on to produce further fission

this takes place in a reaction chamber/ fuel rods

Front 135

What is nuclear fusion?

Back 135

process of forcing two nuclei close enough together so they form one single larger nucleus

Front 136

nuclear fusion happens as

Back 136

they make two light nuclei collide at very high speed

Front 137

fusion is the process by which energy is released in

Back 137

stars

Front 138

nuclei approaching eachother will repel due to their positive charge so to over come this

Back 138

the nuclei must be heated at very high temperatures and reaction must be contained by a magnetic field

Front 139

to reduce exposure to radiation, workers must

Back 139

keep as far as possible from sources of radiation

spend as little time exposed as possible

shield themselves with materials such as concrete and lead

Front 140

most scientists believe earth was created by big bang

Back 140

13 billion years ago

Front 141

protostars are formed by

Back 141

dust and gas being pulled together by gravitational forces

Front 142

the protostar becomes denser and

Back 142

the nuclei of hydrogen and other light elements fuse together. energy is released from process so core gets brighter and hotter

Front 143

stars radiate energy because of

Back 143

hydrogen fusion in core. this stage can continue for billions of years until the star runs of out hydrogen nuclei.

Front 144

a main sequence star is when

Back 144

the star is stable because the inward force of gravity is balanced by the outward force of radiation from core

Front 145

eventually a star runs out of hydrogen nuclei...

Back 145

swells, cools down and turns red

Front 146

Now, if the main sequence star has a low mass...

Back 146

is now a red giant

helium and other light elements fuse to form heavier elements

fusion stops and the star will contract to form a white dwarf

eventually no more light is emitted so it becomes a black dwarf

Front 147

Now if the main sequence star has a larger mass

Back 147

it is a red super giant which continues to collapse

eventually the star explodes into a supernova

the outer layers are thrown out into space and the core is left as a neutron star

if this is massive enough it becomes a black hole

the gravitational field strength of the black hole is so strong that not even light can escape from it

Front 148

chemical elements are formed by

Back 148

fusion processes in stars

Front 149

elements heavier than iron are

Back 149

only formed in the final stages of the life of a big star.

this is because the process requires the input of energy

Front 150

The presence of heavier elements in the sun and inner planets are

Back 150

evidence that they were formed from debris scattered by supernova