# key facts, word equations and rules

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## Electricity

• Current is never used up.
• Current and brightness are similar.
• Current is the opposite to resistance- when one increases, the other decreases.
• Current flows from the posotive terminal of the battery to the negative.
• LDR- in the light- restitance decreases, in the dark- resistance increases.
• Series and parrallel- usually parallel is more useful.
• Short curcuit- wire has no resistance and can become a hazard.
• Diodes- current can only flow in one direction.
• Resistors- increases the resistance so a short curcuit does not occur or prevents a component over heating with too much current.
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## Magnetism

• Like poles repel- opposties attract.
• Use bar magnet or iron fillings to observe magnetic field.
• Pattern- out of north and into south
• Magnetic materials- Nickel, iron, colbalt, steel.
• Iron is a good temporary magnet used in electromagnets.
• Steel is good permanent magnet.
• Freely suspended, magnet aligns itself with Earth's north and south poles.
• Current in coil creates an temporary magnet around soft iron core.
• More current= increases strength of magnet.
• Used in bells and scrap yards for extracting metals from non-metals.
• Relay is magnetic switch.
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## Earth

• Spins on its axis once a day= 24 hours.
• Axis it tilted at 23.5 degrees at its extreme- causes seasons.
• One year= 365 and a quarter days- time for the earth to orbit the sun.
• Moon is the only natural satellite of the earth- 28 days for one orbit.
• Same side of the moon always faces earth.
• Eclipses- Lunar- Moon goes into the earth's shadow, Solar- the moon blocks the sun from view of the earth.
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## Space

• The sun is the closest star to earth out of millions in our galaxy.
• The sun is the centre of our dolar system.
• Nuclear fisions provide the sun's energy.
• Our solar system is made up of the sun, nine orbiting planets, comets, asteroids and moons.
• Earth is the only known atmosphere that supports our life form.
• Satellites are kept in orbit by planet's gravitational pull.
• Moons are non-luminous and reflect the sun's light.
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## Light

• Light is faster than sound.
• It travels in straight lines from a luminous source.
• Objects around have different properties.
• Opaque- does not let light through, causing a shadow.
• Translucent- lets some light through, is blurred. causes a faint shadow.
• Transparent- lets all the light through, causes barely any shadow.
• Some objects reflect the light, however are not luminous.
• Refraction- the bending of light in a boundary between two mediums and densties- changes direction.
• Dispersion-  ehite light splitting into a spectrum.
• Light is a form of energy.
• A light that is invisible to the human eye is called ultraviolet.
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## Sound

• Slower than light.
• Molecules vibrate and are carried to the ear by sound waves.
• Different animals and humans have different audible ranges.
• Cannot travel through a vacuum- unlike light-needs a substance to carry it.
• Sound travels at different speeds in different mediums.
• Reflection of sound is an echo.
• A sound to high for humans to hear is ultrasound.
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