all Sections Flashcards
In a stable atom what is there?
Are the same amounts of positive and negative charges
All electrostatic effects are due to what?
The movement of electrons
What is the law of electric charge state?
That like charges repel and unlike charges attract
When a polythene rod is rubbed with a duster what happens?
Electrons are transferred from the duster to the polythene, making the polythene rod negatively charged
What happens when a acetate rod is rubbed with a duster?
Electrons are transferred from the acetate to the duster, leaving the rod positively charged
What in a general object have
- negative charge due to the excess of electrons
- positive charge due to a lack of electrons
What are ions?
Atoms or molecules that have become charged
What can cause an explosion?
When inflammable gases or vapours are present, or there is a high concentration of oxygen, a spark from static electricity could ignite the gases or vapours and cause an explosion
What happens if a person touches something at high voltage?
Large amounts of electrical charge may flow through there body. Even small amounts of charge flowing through the body can be fatal
What can static electricity be a nuisance not dangerous?
- dust and dirt are attracted to insulators, such as TV screens
- clothes made from synthetic materials often ‘cling’ to each other and to the body
Electric shocks can be avoided in the. Following ways
- if an object that is likely to beome charged is connected to earth, any build-up of charge would immediately flow down the earth wire
- in a factory where machinery is at a risk of becoming charged, the operator stands on an insulating rubber mat so that charge cannot flow through them to earth
- shoes with insulating soles are worn by workers if there is a risk of charge building up so that charges cannot flow through them to earth
- fuel tankers are connected to an aircraft by a conducting cable during re fuelling
What is the things that prevents build-up of charge?
Anti-static spray, liquids and cloths made from conducting materials carry away electric charge
What does a dust precipitator do?
Removes harmful particle from the chimneys of factory’s and power stations that pollute the atmosphere
How do you use dust precipitators?
- a metal grid is placed in the chimney and given a large charge from a high-voltage supply
- plates inside the chimney are earthed and gain the opposite charge to the grid
- as the dust particles pass close to the grid they become charges with the same charge as the grid
- like charges repel, so the dust particles are repelled away from the wires. They are attracted to the oppositely charged plates and stick to them
- at intervals the plates are vibrates and the dust falls down to a collector
- the dust particles gain or loss electrons to become charged
- the charge on the dust particles induces a charge on the earthed metal plate
- opposite charges attract so the dust is attracted to the plate
Static electricity is used in paint spraying, how does it work?
- the spray gun is charged
- all the paints particles become charged with the same charge
- like charges repel, so the paint particles spread out giving a fine spray
- the object to be painted is given the opposite charge to the paint
- opposite charges attract, so the paint is attracted to the object and sticks to it
- the object gets an even coat, with limited paint wasted
What happened of the object to be painted is not charges, the paint move onto it but what?
- the object becomes charged from the paint, gaining the same charge
- the further paint droplets are repelled away from the object
Therefore the object to be painted is given the opposite charge to the paint. If the paint is negatively charged, having gained electrons, the object should be positively charged, by losing electrons
What is a defibrillation?
Is a procedure to restore a regular heart rhythm by delivering an electric shock through the chest wall to the heart
What happens during the procedure of a defibrillator
- two paddles are charges from a high-voltage supply
- they are then placed firmly on the patients chest to ensure good electrical contact
- electrical charge is passed through the patient to make their heart contract
- great care is taken to ensure that the operator does not receive an electrical shock
What changes the resistance?
A variate resistor or rheostat. Longer lengths of wires have more resistance; thinner wires have more resistance
What is voltage (potential difference) measured in?
Volts using a voltmeter connected in parallel
- for a fixed resistor, as the voltage across it increases, the current increases
- for a fixed power supply, as the resistance increases, the current decreases
What is the formula for resistance?
Resistance = voltage/current
What is resistance measured in?
Ohms
What does the live wire do?
Carries a high voltage around the house
What doe the neutral wire do?
The neutral wire completes the circuit, providing a return path for the current
What does the earth wire do?
Is connected to the case of an appliance to prevent it becoming live
What does a fuse do?
Contains wire which melts, breaking the circuit, if the current becomes too large
What does atoms consist of?
Small positively charged nucleus surrounded by an equal number of negatively charged electrons
