Science
- Electrical Systems
10.Transfer of Heat Energy and its effects
- Chemical Changes
- Application of Forces and Transfer of energy
- Atoms and Molecules
Chemical Changes
Physical Changes
No New Product formed + can be reversed
Boiling
Thermal energy
travels from higher temperature region to lower temperature region, until thermal equilibrium is reached
temperature
degree of hotness of a substance
Melting
Freezing
Mixing
Breaking
Dissolving
Bimetallic strips
New substance is formed + difficult to reverse
Chemical reactions
made of two different metal strips joined together
Reactants react with each other to form new products
the strip bends when one metal bends more than the other
Energy such as heat, light or electricity is given out
transfer of energy
Rust
Conduction
transfer of heat through a medium from one particle to another, without the movement of the medium itself
Word Equations
E.g. Magnesium + Oxygen ---> Magnesium Oxide (oxidation)
Thermal decomposition
In thermal decomposition, a single substance breaks up into two or more simpler substances when it is heated.
faster heat conduction in metals
Radiation
Acid with reactive metals
dilute hydrochloric acid + zinc ---> zinc chloride + hydrogen gas
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Acid with metal carbonates
Acid with alkalis
unreactive metals are lead, copper, silver and gold
dilute hydrochloric acid + aqueous calcium hydroxide ---> calcium chloride + water (Neutralisation)
Factors impacting heat gain/loss
dilute sulfuric acid + magnesium carbonate ---> magnesium sulfate + water + carbon dioxide gas
Metals have free moving electrons
when heated, free moving electrons gain kinetic energy
they collide into other particles, transferring energy to them.
Electrolysis
The use of electricity to cause chemical changes
When electricity passes through water, hydrogen and oxygen are produced.
Atoms are the smallest units of an element that can take part in a chemical reaction
colour of object (black,white,dull, shiny)
relative mass and charge of sub-atomic particles
Neutrons (0) = 1
Electroplating (Coating an object with a thin layer of metal)
electrons (-1) = 1/1836
white,shiny,smooth
shiny
good reflector of radiation
black,rough,dull
poor emitter and absorber of radiation
an atom is electrically neutral
Convection
transfer of heat from one place to another by the movement of the medium itself
Indicators
Litmus paper
Red
weight is the force an object exerts, not the mass of an object
heat is transferred through liquids and gases mainly by convection
Blue
Methyl Orange
ways to measure mass
Screened Methyl Orange
Universal Indicators
movement of the water is set up by the differences in densities and is called convection current
Turns blue
Alkaline
Turns Red
Acidic :
Below pH 4
Red
Above pH 4
Yellow
weight is measured in newtons
ways to measure it
extension spring balance
compression spring balance
Below pH 4
Above pH 4
Pink
Green
weighing scale
good absorber and emitter of radiation
electrostatic force
examples of electrostatic force
pressure
dust attracted to plastic wrap
transfer of heat without the need of a medium
hair stand when we wake up
Thymolphthalein
Below pH 10
White
Above pH 10
Blue
factors
force
area
formula
force(newtons)/area(m square)
units
unit for pressure is Pa
pressure in liquid and gases
atmosphere pressure
depth and density of liquid
examples
submarines have rigid metal bodies to withstand the very high pressure deep underwater.If the submarine dives beyond a certain depth, the pressure may become too high and damage the submarine
water supply
water is delivered to and stored in tanks at the top of most high-rise buildings.This causes the pipes below the tanks to beacome high pressure and ensures that water flows to the units below
Electric current
a change in air pressure allow users to drink out of drink boxes using straws.The air in the straw would be sucked by the user.The higher atmospheric pressure would push the liquid upwards through the straw
a change in air pressure cause breathing difficulty. There is lower air pressure at higher altitudes, hence airlines have to pump air into the airplanes to ensure passengers can breathe without difficulty
Potential difference
there is a higher atmospheric pressure than the air pressure in the cup. Hence, it would be held tightly on the wall
Definition: The amount of work done to drive a unit of charge between the two points in an electric circuit OR the amount of energy converted to other forms when a unit of charge flows between the two points in an electric circuit
work done
unit for work done/energy is joule(J)
formula: distance(m) x force(newtons)
Resistance
SI Unit: Volt (V)
non-renewable sources of energy
fossil fuels
renewable sources of energy
Definition: Ratio of the potential difference across an electrical component to the current flowing through it
SI Unit: Ohm (Ω)
hydroelectricity(dams)
Definition: Rate of flow of electrical charges
tidal energy
SI Unit: Ampere (A)
solar energy
wind energy
geothermal
biomass(vegetation etc)
Relationship between resistance, voltage and current --> V=IR
circuit breaker
opens the circuit when the electric current flow is too big
main switch turns on or shuts off all electricity in households
Total Effective Resistance
when the current in one part of the circuit is too big the circuit breaker for that part trips while the others remain switched on
Series
Paralllel
RT = R1 + R2 + ...
RT = (1/R₁ + 1/R₂ + ...)-1.
fuse
select fuse with the correct fuse rating
formula: P/V
Series Circuit
wires
current flowing through each resistor is constant
neutral wire(blue)
the force acting on the like charges repelling each other is called electrostatic force of repulsion
earth wire(green or yellow)
electric charges that do not flow in an electric circuit are called static electricity
unlike charges attract each other,the force acting on the positive and negative charges is called the electrostatic force of attraction
IT = I1 = I2 = I3
Potential difference across each resistor
connect the appliance back to the mains to close the circuit
diverts the excessive current to the ground if a short circuit occurs
V1 + V2 + V3 +... = e.m.f of cell
short circuit
Total resistance in whole circuit
path of very low resistance between 2 parts of a circuit,causing a large current flowing through the circuit, resulting in overheating or even fire
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live wire
connected to the mains,for conducting electricity into the kettle to power the heating element
RT = R1 + R2 +...
types of danger in electrical circuits
As more resistors are added, total resistance increases
Parallel Circuit
Potential difference across each resistor
Total resistance in whole circuit
Current flowing though each branch is equal to current in main branch when added together
RT = (1/R₁ + 1/R₂ + ...)-1.
Constant for all resistors, is equal to e.m.f
IT = I1 + I2 + I3 +...
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As more resistors are added, total resistance decreases
Energy and power
electricity usage in household
kW x h = ___kWh
live wire(brown)
Protons (+1) = 1
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Electronic arrangement of atoms
Group number (vertical) is affected by valence electrons which determines the reactivity of element and chemical properties
Applications in real life
Hydrochloric acid [HCl] is used to remove impurities such as rust from metals
Nitric acid [HNO3] is used in explosives and fertilizer
Sulfuric acid [H2SO4] is used in car batteries, detergents and fertilizers
Aqueous sodium hydroxide [Na(OH)3] is used in soaps
Aqueous potassium hydroxide [KOH] is used in soaps
Aqueous calcium hydroxide [Ca(OH)2] or slaked lime is used to neutralise acidic soil
Period number (horizontal) is affected by electron shells
drawing of diagram: 2 electrons in first shell, 8 max in each following shell, placement in NSEW, remember to have legend/key
Electronic configuration for example 2.8.2 ---> period 3, group 2
Weight=mass X gravitational strength
- Human Digestive System
Digestion
Food Tests
12.Ecology
factors
Important terms
Ecology
The study of interactions between organisms with one another and with their surroundings
Habitat`
The place where an organism lives and reporoduces
Species
A group of interbreeding organisms that do not ordinarily breed with members of other groups
Population
A group of organisms of the same species hat live together in a habitat
Community
All populations that live and interact with one another in a particular habitat to make up a community
Ecosystem
An Ecosystem is a community of organisms interacting with one another and its abiotic environment
abiotic
biotic
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Light intensity
require light energy from the sun to photosynthesis and make food
temperature
water
oxygen content
Iodine test
Benedict's test
Biuret test
Ethanol Emulsion test
affects rate of photosynthesis and growth of plants
enables organisms to see so they can move about to find food and avoid danger
adaptation to winter
plants
animals
-hibernation
migration to warmer climates for birds
adaptation to extreme cold
thick layer of fat