Vocabulary
Word
Meaning
radiate
emit (energy, especially light or heat) in the form of rays or
waves.
Light source
an object that produce light
Opaque
not able to be seen through
Transparent
allowing light to pass through so that objects behind can be
distinctly seen.
Reflection
the throwing back by a body or surface of light, heat, or sound
without absorbing it.
Ray
each of the lines in which light (and heat) may seem to stream
from the sun or any luminous body.
Propagate
to move in some direction or through a medium; transmit
Linear
straight or resembling a line
Periscope
Any of various tubular optical instruments that contain
reflecting elements, such as mirrors and prisms, to permit
observation from a position displaced from a direct line of sight.
Displaced
To move, shift, or force from the usual place or position
Light beam
projection of light energy radiating from a light source or
collection of light rays from a light source.
luminous
giving off light; bright or shining.
Non-luminous
not capable of producing light, but can be capable of reflecting
light from another source.
Sources of light
The Sun, fires and lamps are all sources of light. Mirrors and other objects reflect light. They
do not make their own light.
A source of light makes light. The Sun and other
stars, fires, torches and lamps all make their own
light and so are examples of sources of light.
When a television is turned on, it produces light.
Some animals, such as fireflies and glow-worms, are
light sources. They make their own light to attract mates.

The moon is not a source of light. It reflects light from the Sun.
Transparent, translucent and opaque materials
Transparent
Transparent materials let light pass through them in
straight lines, so that you can see clearly through them.
Glass is an example of a transparent material.
Translucent
Translucent materials let some light through, but they
scatter the light in all directions, so that you cannot see
clearly through them. Tissue paper is an example of a
translucent material.
Opaque
Opaque materials do not let any light pass through
them. They block the light. Wood is an example of an
opaque material.
Shadows
A shadow is made when an object blocks light. The object must be opaque or
translucent to make a shadow. A transparent object will not make any shadow, as light
will pass straight through it.
The following three things are required for a shadow to form
a source of light
an opaque object
a screen or surface behind the object


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Opaque objects make dark shadows. Translucent objects make faint shadows.

If an object is moved closer to the light source, the shadow gets bigger.

If an object is moved further away from the light source, the shadow gets smaller.
Characteristics of a Shadow:
A shadow has the following three characteristics:



It is always black, regardless of the colour of the object used to make the shadow
It only shows the shape or outline of the object and not the details.
The size of a shadow varies depending on the distance between the object and
the source of light, and the distance between the object and the screen.
Shadows made by the Sun
The Sun is a very bright natural light source. It seems to move across the sky during the
day. In fact it just looks like it does that because the Earth is spinning.
The Sun casts (makes) the longest shadows at the beginning and end of the day that
means, during early morning and just before sunset, when the Sun is lowest in the sky.
The Sun casts the shortest shadows at midday, when the Sun is highest in the sky.
Sundial, the earliest type of timekeeping device, which indicates the time of day by the
position of the shadow of some object exposed to the sun’s rays. As the day progresses,
the sun moves across the sky, causing the shadow of the object to move and indicating
the passage of time.
Reflection of light
When light falls on a highly polished surface like a mirror most of the light is sent
back into the same medium. This process is called “ reflection of light”.
• Reflected Ray – leaves mirror and strikes your eye
your eye
• Incident Ray – leaves the object and strikes the mirror
When rays of light reflect, they obey the law of reflection:
Law of reflection of light.
 The angle of incidence is equal to the angle of reflection.
Angle i = Angle r
 The incident ray , the reflected ray and the normal at the point of
incidence all lie on the same plane.
Types of reflection
1. Irregular or Diffused reflection : -
When light strikes a rough and dull surface , it bounces back in all directions
(scatters) giving rise to general illumination. It helps us to see things.
2. Regular or Specular reflection :-
When light reflects a smooth or shiny surface, it gets reflected in the same
medium forming image of an object.
Uses of reflection of light
1. Reflection help us to see nonluminous objects around us.
2. Reflection help us to see our image on the mirror
3. The vehicles’ side mirror enables the driver to see things behind the vehicle.
4. Reflective safety jackets helps to identify a person from a long distance
especially if there is poor lightening.
Sound – File notes
`
What Is Sound?
Sound is an energy, caused by vibration that creates waves.
How Sound Is Made?
Like light, sound travels through the air in waves. But sound travels
slower than light .
 Sound is made by air molecules vibrating.
 When you clap your hands, the air around your hands shakes.
This is the air molecules vibrating
 The vibration of the air molecules around the clapped hands shakes the
molecules around them. The molecules continue to shake the molecules
next to them until the air molecules in the ears are vibrating.
 When air molecules inside the ears vibrate, they
shake tiny hairs on the insides of the ears.
 The hairs are connected to nerves under the skin.
 These nerves send messages to your brain to tell
you that you heard a noise.
Sound needs molecules to move. It is impossible for sound to travel
in space.
Sound doesn’t have to move through air. It can travel through water or metal.
In fact, sound travels faster through water and solids than it does through air.
Loud and Quiet
The louder the sound, the bigger the vibration.
The size of the vibration is called the amplitude
Quieter sounds have smaller amplitude, and
louder sounds have a bigger amplitude.
How Does Sound Travel?
Sound can travel through solids, liquids and gases.
Sound travels as a wave, vibrating the particles in the medium it is travelling in.
Sound wave is an example of longitudinal waves.
What are longitudinal waves?
In a longitudinal wave, the particles vibrate back and forth, so the direction of its
movement is parallel to the direction of the wave.
What are the parts of a longitudinal wave?
 Compression
 Rarefaction
Parts of a longitudinal wave are compression (particles are closer) and rarefaction
(particles are further apart).
Properties of sound –pitch and amplitude
Properties of Sound
\ crest
The Relationship between Pitch, Frequency and
Wavelength.
 Pitch is a measure of how high or low a sound is. A
whistle being blown creates a high-pitched sound.
A rumble of thunder is an example of a low-pitched
sound.
 Frequency is the number of peaks of waves per
second.The more peaks in this time, the higher the pitch. Frequency is
measured in a unit called Hertz (Hz).
 Wavelength is the distance between two peaks or two troughs of waves. A
higher pitched sound has a shorter wavelength.
Amplitude
 Amplitude is the height of the wave,
measured from the peak to the
trough.
 Higher amplitude, like the wave on
the right, means higher volume.
 Lower amplitude, like the wave on the left, means lower volume.
 The size of the vibration is called the amplitude .
Louder sounds have a larger amplitude, and quieter sounds have a smaller
amplitude.
Measurement of Sound






We commonly measure sounds audible to humans in decibels, dB
Human ears can be damaged by sounds louder than 85 decibels.
Sound frequency is measured in a unit called Hertz (Hz).
10 Hz means that 10 soundwaves pass a given point in 1 second.
Humans can normally hear sounds between 20 and 20,000 Hz.
Sound is measure by a device called sound level meter.
Muffling sound
Muffle is to quiet a sound, usually by wrapping it with something.
Ways to muffle sound.
 Loud sounds can hurt our ears. Some people work in very noisy places. They
need to protect their ears. They wear ear defenders. Ear defenders muffle
sound.
 In buildings we use carpets and curtains to muffle noise. Sometimes the spaces
between walls are filled with materials that don’t let noise through.
 Walls can be covered with material to muffle sounds.
 We fit silencers to cars, trucks and motorbike to muffle the sounds of their
engines.

Animals’ Hearing
Elephants
Human
Some dolphins
can
earsdetect
canand
detect
even
batslower
a can
range
hear
frequencies
of frequencies
than of
up
humans
20
to –
120,000
20,000
(from Hz.
14
Hz.Hz).
Ultrasound and Infrasound Waves
Ultrasound waves have frequencies too high for humans to hear and
shorter wavelengths than other sound waves.
Infrasound waves have frequencies too low for humans to hear.
Uses for Ultrasound and Infrasound
Waves
Ultrasound waves can reflect more easily than other sound waves. They
are useful in:
medical
imaging
non-destructive
testing of
mechanical
equipment
medical
uses
sonar
Infrasound waves can record earthquakes that humans may not feel.
Electric circuit –file notes
Key words
1
2
electricity
circuit
3
battery
4
5
6
7
8
9
10
terminal
positive terminal
negative terminal
electric current
electric voltage
parallel circuit
series circuit
11
direct current
12
alternate current
13
conductor
14
insulator
a form of energy
path through which electric current flows
a group of cells.
Battery is the power source required to drive charges in a closed circuit.
an end point
the highest energy potential of a battery
the lowest energy potential of a battery
the flow of charges in a closed circuit in one second
the energy produced by a battery to drive the charges in a circuit
a circuit where electric devices are connected in several branches
a circuit where electric devices are connected one after the other
one-way flow of charges from a battery.
the direction of flow of charges is from the positive to negative terminal of a battery.
two-way flow of charges from a power source. The direction of flow of charges
changes at every equal interval of time.
material that allows the flow of electric current. [Eg. all metals]
material that does not allow the flow of electric current.
[ Eg. paper, wool, cloth, plastic, hair, rubber, air]
Types of electric current

Alternating current (AC)
 Direct current (DC)
Electric bulb
Electric circuit
A circuit is the closed path that an electric current travels on, and a simple circuit usually
consisting of a power source (a battery), a switch, a light bulb and conducting wire.
Electrical circuit symbols
Types of circuit:


Series circuit
Parallel circuit
Series circuit
•
•
•
The components in the series circuit are connected one
after another
The current is the same everywhere in a series circuit. It
does not matter where you put the ammeter, it will give
you the same reading.
The current in a series circuit depends upon the number of
cells. The more cells you add, the greater the current.
•
When more lamps are added in series circuit, current decrease and brightness of the
lamp also decrease.
•
Each lamp is depending on each other
•
In series circuit, if you make a break anywhere along the loop, the current stops flowing
and the circuit will not work.
Parallel circuit
•
In a parallel circuit, the components are connected side by side.
This gives the current several different paths for it to flow
around.
•
If one bulb blows, the other bulbs will remain lit as the circuit is
still complete.
•
In a parallel circuit, the voltage across each component is the
same.
•
In a parallel circuit , if there is break somewhere in the pathway, but
since each branch has its own independent path, a break in one branch
does not affect the devices in other branch
•
In a parallel circuit the total current is equal to the sum of each branch or loop of the
circuit.
Factors affecting brightness of bulb in series circuit :
•
•
Number of components ( increasing or decreasing the number of components )
Number of batteries