science exam!

• Neutralization

  Acid + alkali → salt + water
• Neutralization when acid pour into alkali or alkali pour into acid

  • pH in acid: increases
  • pH in alkali: decreases
• Eye structure


  • Focusing muscle changes the thickness of the lens
  • Sclera protects the eyeball and maintains the shape
  • Cornea lets light pass through and helps focus light
  • Iris controls the size of the pupil
  • Pupil regulates the amount of light entering the eye
  • Lens helps focus light
  • Jelly-like fluid maintains the shape of the eyeball and helps focus light
  • Retina contains light-sensitive cells that detect light and produce signals
  • Blind spot is the spot where the optic nerve leaves the eyeball and contains no light-sensitive cells
  • Optic nerve transmits signals from light-sensitive cells to the brain
• Ear structure


  • Pinna is the outer ear
  • Ear canal is in outer ear
  • Eardrum is in middle ear
  • Ear bones is in middle ear
  • Cochlea is in inner ear
  • Auditory nerve is in inner ear
• Changes of light

  1. Pupil size

  2. Iris

  3. Lens thickness
• Short sight


  Image formed in front of retina
• Long sight


  Image formed behind the retina
• Correction for short sight and long sight

  • Concave lens
  • Convex lens
• Pinna


  The funnel-shaped part of the outer ear that collects sound from the surroundings and directs it into the ear canal
• How we hear


  1. Sound travels down the ear canal

  2. Sound causes the eardrum to vibrate

  3. Vibrations are transmitted to the ear bones

  4. Ear bones amplify the vibrations and transmit them to the inner ear

  5. Sensory hair cells in the cochlea detect vibrations and produce signals

  6. Signals from the sensory hair cells are sent to the brain through the auditory nerve

  7. Brain interprets the signals as sound
• Outer ear

  • Pinna
  • Ear canal
• Middle ear

  • Eardrum
  • Ear bones
• Inner ear

  • Cochlea
  • Auditory nerve
• Auditory nerve


  • Transmits signals from sensory hair cells to the brain
• Jelly-like fluid,cornea and lens


  Helps focus light onto the retina
• How an image is formed in the eye

  1. Light from an object enters the eye through the cornea

  2. Cornea, lens and jelly-like fluid focus the light onto the retina

  3. A sharp and inverted image is formed on the retina

  4. Light-sensitive cells on the retina are stimulated to produce signals

  5. Signals are sent to the brain through the optic nerve

  6. Brain interprets the signals as an upright image
• Retina


  • Contains light-sensitive cells that produce signals
• Optic nerve


  • Transmits signals from the retina to the brain
• Indicators


  • Litmus paper & solution
  • Universal indicator
  • pH paper
  • pH meter
  • pH sensor with data-logger
• Litmus paper & solution

  • Convenient to carry around
  • Cheap
  • Easy to use
• pH meter

  • More accurate
  • Can be reused
  • Can be used to measure pH value of a liquid with dark colour
• pH sensor with data-logger

  • Monitor the change in pH value during the experiment
  • pH curve is plotted automatically
• Natural indicators

  • Contain pigments which change colour in the presence of an acid or an alkali
  • Example: red cabbage, strawberry, red rose flower, etc...
• Neutralization

  A chemical reaction when acids and alkalis react with each other
• Neutralization experiment

  1. Transfer some neutralized solution to a watch glass

  2. Heat the watch glasses over a water bath until all liquids have evaporated to dryness

  3. Put a slide above watch glass during evaporation
• Some white solids remained on the watch glass after neutralization
• Dry cobalt chloride paper turns from blue to pink
• Salt and water are produced when neutralization occurs
• Force

  Push and pull the object
• Effects of motion


  • Start to move
  • Move faster/ slower
  • Stop
  • Change direction
• Mediums for sound to travel through

  • Solid
  • Liquid
  • Gas
• Sound

  Vibration made by a vibrating object
• Frequency

  Number of vibrations per second
• Hertz


  Unit of frequency
• Sound cannot travel through a vacuum
• Sections of the human ear


  • Outer ear
  • Middle ear
  • Inner ear
• How we see objects at different distances

  1. Looking at a near object:

  2. The focusing muscles contract

  3. The lens becomes thicker

  4. Looking at a distant object:

  5. The focusing muscles relax

  6. The lens becomes thinner
• Light-sensitive cells on the retina

  • Cone cells
  • Rod cells
• Cone cells

  • Three types, each sensitive to one of three colours: red, green and blue
  • Sensitive to bright light and colour
• Rod cells

  • Sensitive to dim light but cannot detect colour