Topic 11 - Static Electricity Flashcards
Paper 2
What is static electricity?
+Electricity that builds up on insulating materials and often ends with a spark or shock
+The build up of charge on insulating materials
What is build up of static caused by?
Friction
What happens when certain insulating materials are rubbed together?
+Negatively charged electrons will be scraped of one, and transferred to the other
What happens to the electrons when they are on insulating materials?
+They are not free to move
+This build up of charge is called static electricity
What happens when insulating materials are electically charged by static electricity?
+When the material becomes electrically charged, there is a positive static charge on the one that has lost electrons and a negative static charge on the one that has gained electrons
+Both charges are equal
Which electrons always move?
The negative electrons
What happens when you rub a duster with a polythene rod?
+The rod gains electrons and becomes negatively charged
+The cloth becomes positive
What happens when you rub a duster with a Acetate rod?
+The Acetate rod loses electrons and so becomes positive
+The cloth becomes negative
What do electrically charged objects do?
They exert a foce on one another
What are two things with opposite electric charges?
+They are attracted to each other
+These forces get weaker the further they are
What are two things with the same electric charge?
+They repel each other
+These forces get weaker the further they are
What practical can you do to see the repel and attract forces of static electricity?
- Suspend a rod with a known charge on a piece of string [so it is free to move]
- Placing an object with the same charge nearby will repel the rod [the rod will move away from the object]
- An oppositely charged object will attract the rod, [causing it to move towards the object]
What can electrically charged objects also attract?
Uncharged objects
What does rubbing a balloon against your hair or clothes do?
+The rubbing transfers electrons to the balloon, leaving it with a negative charge
What happens if you hold a negatively charged balloon against the wall?
+It will stick - even though the wall isn’t charged
Why can a negatively charged balloon stick to the wall?
+The charges on the surface of the wall can move a little,
+The negative charges on the surface of the wall repel the negative charges of the balloon
+This leaves a positive charge on the surface, which attracts the negatively charged balloon [attraction by induction]
What is attraction by induction?
+Where there is a positive charge on a surface, which attracts a negatively charged object
What is another example of attraction by induction?
+If you run a comb through your hair, electrons will be transferred to the comb, making it negatively charged.
+It can then be used to pick up little pieces of uuncharged paper
+Holding it near the pieces of paper causes induction in the paper, meaning they jump and stick to the comb
What does too much static cause?
Sparks
What happens as an electric charge builds on an object?
+The potential difference between the object and the earth [which is at 0V] increases
How is a spark caused?
+When the potential difference gets large enough, electrons jump across the gap between the charged object and the earth
+This usually happens when the gap is fairly small
Where can electrons also jump to?
+They can jump to any earthed conductor that is nearby
+This is why you can get static shocks from clothes or getting out of a car
+This usually happens when the gap is fairly small
Where can static electricity be used?
+In electrostatic sprayers
+Photocopiers
+Industry
Where are electrostatic sprayers used?
+In various industries, to give a fine, even coat of whatever is being sprayed.
+For example electrostatic paint sprayers
What things are painted using electrostatic paint sprayers?
Bikes and cars
How do electrostatic paint sprayers work?
+The spray gun is charged - which charges up the small drops of paint
+Each paint drop repels all the others [since they’ve all got the same charge] so you get a very fine, even spray
+The object to be painted is given an opposite charge to the spray - this attracts the fine spray of paint
+This gives an even coat of paint and hardly any is wasted
+Parts of the object that are not in direct focus of the spray can still recieve paint [there are no paint shadows]
How do insecticide sprayers work?
+The plants are not given an opposite charge
+The plants charge by induction as insecticide droplets come near them
What are the dangers of static electricity?
+Refuelling cars
+Static on airplanes
+Lightning
What are the dangers of static electricity when refuelling cars?
- As fuel flows out of a filler pipe [eg. into an aircraft or tanker], then static can build up.
- This can easily lead to a spark - which might cause an explosion in dusty or fumey places [like when filling up a car with fuel at a petrol station]
What are the dangers of static electricity on airplanes?
- As planes fly through the air, friction between the air and the plane causes the plane to become charged.
- This build up of static charge can interfere with communication equipment.
What are the dangers of static electricity in lightning?
+Raindrops and ice bump together inside storm clouds - leaving the top of the cloud postively charged and the bottom of the cloud negative.
+This creates a huge voltage and a big spark, which can damage homes or start fires when it strikes the ground
How can you reduce the dangers of static electricity?
+By earthing charged objects
How can we stop electrostatic charge building up?
+Objects can be earthed
How can dangerous sparks be prevented?
+By connecting a charged object to the ground using a conductor [e.g copper wire]
+This is called earthing
What does earthing provide?
+An easy route for the static charges to travel into the ground.
+This means no charge can build up to give you a shock or make a spark.
Where do the electrons flow if the charge is negative or positive?
+The electrons flow down the conductor to the ground if the charge is negative
+The charge flows up the conductor from the ground if the charge is positive
What objects must be earthed to prevent sparks?
+Fuel tankers must be earthed to prevent any spakrs that might cause the fuel to explode
What is an electric field?
+An invisible field that is created around any electrically charged object
+It’s the region around a charged object where, if a second charged object was placed inside it, a force would be exerted on both of the charges
What happens to the strength of the field the closer an object gets?
+The closer to the object you get, the stronger the field is
+The further you are from it the weaker it gets
How can you show an electric field around an object?
+Using field lines
+Eg. you can draw the field lines for an isolated [ie. not interacting with anything] point charge
Where do electric field lines go from?
+Positive to negative
+They’re always at a right angle to the surface
What happens to the field the closer the lines are?
+The closer the lines are, the stronger the field is
+The further from a charge you go, the further apart the lines are and so the weaker the field is
What does a positive electric field look like?
+Field lines go outwards
What does a negatve electric field look like?
+Field lines go inwards
What do electric fields cause?
Electrostatic forces
What happens when a charged object is placed in an electric field?
+When a charged object is placed in an electric field, it feels a force
+This force is caused by the electric fields around two charged objects interacting
What happens when the field lines between the charged objects point in the same direction?
+The field lines join up and the objects are attracted to each other
+The objects are oppositely charged
What happens when the field lines between the charged objects point in opposite directions?
+The field lines “push against” each other and the objects repel each other
What does a uniform field look like between two oppositely charged parallel plates?
What do you need to remember when drawing a uniform field?
+You need to show at least three field lines, parallel and all the same distance apart
+You need to draw arrows on your field lines
What is the same between the two parallel plates?
+The strength and direction of the field is the same anywhere between the two plates [its only different at the very ends]
What happens when an object becomes statically charged?
+It generates its own electric field
What are the cause of the events of sparking?
+Interactions between the electric field [of a statically charged object] and other objects
+Eg. a comb, after it’s run through hair, it’s charged and so produces an electric field. - This electric field interacts with the pieces of paper [without touching them] and so they feel a force.
+The force causes them to move towards the comb [and some will even stick to it]
+Sparks are caused when there is a high enough potential difference between a charged object and the earth [or an earthed object].
+A high potential difference causes a strong electric field between the charged object and the earthed object.
+The strong electric field causes electrons in the air particles to be removed [known as ionisation].
+Air is normally an insulator, but when it is ionised it is much more conductive, so a current can flow through it. This is the spark.
