-In the nucleus are positively charge protons and neutral neutrons
-Surrounding are negatively charged electrons
-Usually, no. electrons = no. protons
-More protons than electrons = positively charged
-More electrons than protons = negatively charged
-Equal pos and neg charge = neutral or uncharged
Static Electricity:
-charge = addition or removal of ELECTRONS (unlike protons, they are not held together and so can be easily moved)
Static electricity is due to the buildup of charge in some objects by:
1. Friction: neutral to neutral: Rub plastic with wool--> electrons move from wool to plastic --> wool is positively charged having lost electrons, plastic is negatively charged having gained electrons
2. Contact: charged to neutral: neutral substance gains or loses electrons
-Static electricity can leak slowly through substances such as rubber or air
3 LAWS:
-Unlike charges ATTRACT
-Like charges REPEL
-Charged objects ATTRACT uncharged objects*
Note: The larger the charge difference, the stronger the attraction/repulsion
*eg. Neg rod near neutral paper, pos from paper is attracted to surface closest to the rod, if strong enough, paper may be pulled to rod due to attraction
Other examples:
-wiping surfaces with a cloth leaves electric charge which attracts light, neutral dust particles
-TV and computer screens also attract dust when in use
-Walk on a carpet, friction gives electric charge
-Small electric shock when charges move very quickly to/from your body
-Moving car shares electric charge with passengers, shock as charge moves to the ground via body
-Lightning occurs when movement of particles within a cloud causes the top to be positively charged and bottom to be negatively charged, when the neg builds up it moves to ground or other clouds as a spark of lightning
-An electric field is the area around a charged object
THE ELECTROSCOPE:
-Positive charges DO NOT move
Situation 1: Neg rod, neg repelled down, leaf diverges because negatives are now all at the bottom and like charges repel
Situation 2: Pos rod, neg attracted to the top, leaf diverges because only pos is left at the bottom and like charges repel
Situation 3: Pos rod, neg attracted to top, pos rod touches, neg jumps onto the rod, rod taken away, leaf diverges because only pos is left on the electroscope and like charges repel
Situation 4: After situation 3, finger touches electroscope, pos attracts neg from your finger, electrons jump to electroscope, leaf goes back to original state (this is earthing)
Circuits and Currents:
-For a globe to light up, the circuit must be complete
-A closed switch will complete the circuit
-An open switch will make the circuit incomplete
-A complete electrical circuit is a continuous pathway where electricity can flow
-Power supply: provides electrical energy, battery or power point
-Load: electrical energy is changed into other forms of energy, globe
-Conducting path: allows electrical energy to flow around the circuit, wires
-Current: measure of how much electrical charge passes through a point in the circuit in one second or rate of flow of charge, amperes or amps or A
-Voltage (aka potential difference): energy carried by the charge or amount of energy contained in electrons flowing in an electric circuit, unit is volt
SERIES OR PARALLEL:
-Series: all components are connected in a single path so there is only one path for electrons to flow
-the more light bulbs, the dimmer all the lights will be (with 3 in a series, each gets one third of total voltage)
-if one goes out, they will all go out
-it doesn’t matter which globe goes out
-Parallel: there is more than one continuous path for the electrons to flow
-with more light bulbs, the brightness is still the same as having just one (each globe uses the full voltage of the battery)
-if one goes out, others are unaffected
-it (obviously) does not matter which one goes out
USING A MULTIMETER:
To measure current (in amperes, A) we use the multimeter as an ammeter connected in series
To measure voltage (in volts, V) we use the multimeter as a voltmeter connected in parallel
-Below, the ammeter would replace one globe in series circuit 2, the voltmeter would replace one globe in the parallel circuit
CONDUCTORS AND INSULATORS
The size of the electric current depends on resistance.
-little resistance = large current
-materials with little resistance = conductors = most metals
-materials with a lot of resistance = insulators = many nonmetals such as air, rubber
-filaments, in heating elements, have some resistance causing charge to release energy in the form of heat as it tries to get through
Note: Current is measured in A (amperes) or mA (milliamperes). 1000mA=1A
BATTERIES
-a battery is made of two or more cells, although it more often refers to a single cells (eg the things we put in torches)
-A cell has two electrodes and a substance for electric charge to flow through (electrolyte)
-when two electrodes are joined by a conducting path, a chemical reaction releases charge and allows current to flow
-dry cells are filled with a paste of chemicals
General purpose dry cell:
-electrodes are a central carbon rod on pos terminal and zinc case touching the neg terminal
-reaction between zinc and paste = charge allowing current to flow
-separating layer stop reaction while battery is not in use
-Alkaline cells allow greater electric current to flow
-ideal for heavy-duty torches, digital cameras
-Mercury cells have a steadier voltage than dry cells
-ideal for hearing aids, watches, calculators
LEMON/GRAPEFRUIT BATTERY
-Lemon/grapefruit with 2 metals, wires and an LED
-We know it works because the LED lights up
-The more fruit connected in series, the higher the electric current
-The electrode = the two metals
-Electrolyte = acid in the lemon/grapefruit juice
-Lead dioxide car batteries and nickel-cadmium mobile phone batteries are rechargeable
-A battery charger can be used to reverse the reaction that causes electric current to flow
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