SP11- Static Electricity Flashcards
Why can plastics collect a charge
Because they are insulators - the charge can’t flow through the plastic into other materials
How does a charge occur on an acetate rod and dry duster
When the rods rubbed with the duster _ some electrons move from the acetate to the duster to give it a negative charge and leaving rod with positive charge
When you rub a polyethene rod with a duster - electrons move from duster to rod so the opposite situation occurs
Tell me about opposite charges and reaction
There is a force of attraction between Rods with opposite charges and if they can move - will move towards each other, rods with the same charge repel eachother
Give me an example of static electricity with hair
A child’s hair can become charged, the charge can’t flow away to surroundings, since all hairs have the same charge they repel and spread out
What is charging by induction
A charged object can affect the distribution of charges on an uncharged object
Eg. If a negatively charged ballon is near a will - electrons on wall surface are repellled so the surface of the wall is positively charged - no charges are transferred from the balloon so we say the positive charge on the wall has been induced - this is called charging by induction
How does an electric shock occur
When you walk across some types of Carpet you can end up with an unbalanced charge - if you then touch a conductor such as a metal tap - electrons will flow between the two and you,sometimes there is a spark and you may feel a small electric shock
What’s discharged or earthed
The electrons flow in whichever direction removes the excess charge
Earthed - when we have a negative charge and electrons move to earth
Discharged - when we are positive and gain electrons from an object
How is lightning caused
Static builds up in clouds due to friction between particles of ice or water moves by air currents, when the charge is large enough, charged particles travel through the air between the cloud and the earth - this causes both lightning and thunder
What do we do about lightning (BEcause it’s dangerous )
So to discharge clouds safely, buildings are earthed by having lightning conductors made of thick metal running down from their tops into the earth
How can sparks be dangerous in airplanes
Sparks can be dangerous eg , When there is fuel vapour that could ignite - this can be a problem when refuelling aircraft, which often become charged when flying through the air
A charge can also build up when fuel flows through a pipe, to prevent a spark between a fuel pipe and an aircraft - a bonding line is connected to earth the aircraft before refuelling begins
How are petrol filling stations made safe from sparks
Storage tanks, pipes and hoses are earthed. Cars are earthed through their tyre which contains a form of carbon which makes them conducting
You are earthed when you touch the metal of the car pump
How do electrostatic sprayers work with spraying crops
It makes use of static electricity, electrodes on the spray nozzle charge the insecticide droplets as they pass, the charged droplets spread out because they repel eachother and then they are attracted to the plants by induction - spray spreads around the plant and less falls to the ground so farmers don’t need to use as much
What is a force field
It’s the volume space around an object in which another object can experience a force
What does a charged object have as a force field
An electric field (or electrostatic field)
Another charged object placed in the field will experience a force
The middle part (point where there’s a charge) is called a point charge, lines are called field lines in a diagram
Tell me about field lines in an electric field
Lines will:
Never cross
Show where field is strongest - lines closest
Show the direction of the force on a charge (positive away)
Start on a positive object and end up on a negative object, if only one object, lines will continue to spread
