pre-ib grade 9 science exam revision

triboelectric series

triboelectric series

since different materials hold onto their electrons with different strengths, the triboelectric series helps us to understand which materials would gain or lose electrons when rubbed together!

grounding

we assume that all excess electrons move from a smaller conductor to a larger conductor. electrons will move from the smaller to the larger (ground) until all excess electrons move, making it neutral

charging by induction

1. a charged object is brought near a neutral object; polarizing it

   • another larger conducting object touches the neutral object allowing the flor of electrons to a ground

2. after the conductor is removed, this results in a permanent change left upon the subject

conductor

materials that allow electrons to move easily

the solid matter assumption

small negatively charged particles have the ability to move. protons do not move

power formula

P = I ΔV

• P = Power (W)

• I = Current (A)

• ΔV = Potential Difference (V)

Ohm’s Law (definition and formula)

Ohm’s law states that the potential difference of a circuit is proportional to the current running through it provided that the physical properties of the conductor stay constant

V = IR

• V = Potential Difference (V)

• I = Current (A)

• Resistance = Resistance (Ω)

potential difference (definition)

related to the amount of energy per charge required to move a positive test charge between two points

change in electric energy (formula)

Δe = qΔv

• Δe = change in electric energy (J)

• q = charge (C)

• Δv = potential difference (V)

equivalent resistance (definition and formulas)

the measure of how much resistance is provided by all the resistors calculated by taking the voltage across the battery and dividing it by the current that goes through the battery
resistance = V/I

• in a series connection: R[total] = R1 + R2 + R3…

• in a parallel connection: R[total] = 1/R1 + 1/R2 + 1/R3…
  

energuide and energy star

energuide is a label found on househould appliance in markham stating the amount of energy the product uses in one year of normal use
energy stars are given to any household appliance that uses 10-50% less energy compared to the standard product

power (definition and formula)

how much energy is provided or released by a component in a circuit

P = IΔV

• P = power (W)

• I = current (A)

• V = potential difference (V)

to turn into kW /100

absorption spectrum

when light is shined on atoms, specific colours of light will excite the atoms and become absorbed. these colours disappear from the full spectrum and appear as black lines. atoms absorb and emit the same colours of light

stellar composition

the main elements in most stars are hydrogen and a bit of helium since their particle collisions are so strong that they bump right off the nuclei

stellar equilibrium

in order for a star to maintain stellar equilibrium, it must have a balance of the inward pull of gravity and outwards pressure caused by particle collision. for this to happen, stars must have a steady supply of thermal energy to replace the energy it loses from space

nuclear fusion

in the core of the star, very great pressure occurs. the nuclei of atoms are pushed so close to one another that they forge one large nucleus which produces a tremendous amount of energy

photons/electron shift

when an electron moves from a higher energy level to a lower energy level, it releases energy in the form of a photon. the energy of a photon is equal to the difference of energy between the two levels

ionization

the process by which electrically neutral atoms/molecules are converted to electrically charged atoms/molecules through gaining or losing electrons

the harvard classification scheme

the colour of stars determines its temperature range. scientists use a spectrogram to analyze the spectrum of a star using the harvard classification scheme. this categorizes stars by letter depending on their colour.

• O : blue - > 25 000ºK

• B: blue/white — 11 000-25 000ºK

• A: white — 7500-11 000ºK

• F: white — 6000-7500ºK

• G: yellow — 5000-6000ºK

• K: orange — 3500-5000ºK

• M: red — <3500ºK

the expansion of the universe

space itself is stretching outwards, carrying distant galaxies apart from one another. therefore, the universe is always expanding in size and galaxies are becoming further apart

the big bang theory

the big bang theory hypothesizes that the universe started at a tiny point and then expanded rapidly in a massive explosion approximately 14 billion years ago

unusual characteristics of stars and what they indicate

• lines narrower - giant stars

• lines shifted - red (or blue) shift

• inverted colours - nebula (emission spectrum)

• colours brighten/dim - star is expanding and contracting

• lines move randomly - star is in orbit of another star

• lines move similarly - star is orbiting a large planet

HR diagram (hertz-russel diagrams)

uses star characteristics such as mass, colour, temperature, and luminosity and sees relationships between the differences

• main sequence stars: range in temperature/luminosity/size; stretch diagonally across an HR diagram

• red supergiants: have low temp, but high luminosity; located top right corner of diagram

• red giants: located upper right: smaller mass, low lumonisty

• white dwarfs: hot, dense, small, faint; lower left corner

bohr-rutherford’s gold foil experiment

ernest rutherford conducted the gold foil experiment where he shot positvely charged aplpha particles through a thin piece of foil. most particles passed straigth through while others went in different directions. this proved that:

1. atoms contain a small positvely charged nucleus; which repels positve charges

2. particles are mostly empty space

isotopes

isotopes are elements with the same number of protons/electrons but different number of neutrons. two ways of identifying an isotope is through

1. their mass number

2. their atomic notation

characteristics of transition metals

hard, strong, and lustrous with high melting and boiling points. transition metals make good conductors

electric shielding

when inner electrons of an atom reduce attraction between nucleus and other electrons

• the more inner electrons an atom has, the larger its size, the more electron shielding

• since there is less shielding, atoms with less shells will be more reactive since they have more attractive energy from the nucleus

molecule

two or more atoms connected by chemical bonds that are the same or different

particle

a small object that can have different properties (e.g. mass, volume, density)

evidence of a chemical change

COBLSS

• change of colour

• a change of odour

• bubbles are seen (without heating)

• a change of light, temperature or sound

• a solid is seen

properties of ionic compounds

• crystals

• high melting/boiling points

• solid/hard

• brittle

• usually soluble

• electrolyte/conductive

properties of covalent compounds

• solid/liquid/gas

• lower melting/boiling points

• non-electrolyte — not conductive

• non-soluble

• flammable

algae growth throughout the year

photosynthesis - algae uses this process to convert CO2. this allows algae to produce their own food. generally, photosynthesis is higher in the spring/summer

cellular respiration - allows algae to use the energy it stored. generally occurs more during the winter where oxygen is more available

decomp - decomposers like fungi and bacteria is most common in autumn with right temperature, moisture and availability to oxygen