Topic 11 static electricity Flashcards
Explain how an insulator can be charged by friction, through
the transfer of electrons
Electrons are transferred between insulating materials when they are rubbed together.
This is called charging by friction.
Some materials tend to gain electrons (see polythene rod),
gaining a net negative charge. Others tend to lose electrons (see perspex), gaining a net positive charge.
Recall that like charges _____ and unlike charges _____
repel
attract
Explain common electrostatic phenomena in terms of movement of electrons, including
a shocks from everyday objects
a) As the electric charge builds up, the potential difference between the earth and your foot increases.
Since your body is a conductor, the electrons are able to jump through your body, charging you either positively or negatively
Electrons flow between the metal object and you. There is a spark and you feel a small electric shock
Explain common electrostatic phenomena in terms of movement of electrons, including
b lightning
Static electricity builds up in the cloud due to friction between particles moved by air currents.
The negative charges in the clouds get concentrated towards the bottom of the cloud while the positive charge get pushed to the top of the cloud.
This leaves the earth/ground/objects on it with a positive charge.
When charge is large enough, charged particles travel through air between cloud and the earth as unlike charge attracts.
This causes lighting and thunder
Explain common electrostatic phenomena in terms of movement of electrons, including
c attraction by induction such as a charged balloon attracted to a wall and a charged comb picking up small pieces of paper
By rubbing a ballon onto something rough like hair, charging by induction occurs and both objects become charged (positively or negatively)
When a balloon comes in contact with a wall, it sticks on because the like charges from the balloon to wall repel while the opposite attract since the balloon is charged with mostly positive/negative ions
This makes the balloon able to stick
Same with comb but for rubbing with a cloth instead
How does earthing remove excess charge
It provides a path with low resistance for the electrons to flow either from the device or towards the device to the charge build up, reducing the chance for a spark/shock
Explain some of the uses of electrostatic charges in everyday
situations, including insecticide sprayers
Insecticides
Insecticide sprays from aircraft can be electrostatically charged so that they cover a large area. With this method there is less risk that some of the spray will blow away or fall unevenly. The droplets of insecticide are all given the same static charge as they leave the aircraft.
The static drops spread evenly as they all have the same charge and repel each other. They are also attracted to the earth, so will fall quickly and are less likely to blow away.
Describe some of the dangers of sparking in everyday situations, including fuelling cars, and explain the use of earthing to prevent dangerous build-up of charge
If the charge is very large, a spark to the earth may happen unexpectedly. Sparks like this can be dangerous, potentially igniting a fire. A build-up of static charge is a potential danger when refuelling aircraft or vehicles. Fuel running through the pipes can provide the friction needed to create a static charge. To prevent this, aircraft are earthed with a conductor during re-fuelling.
All charged objects can be discharged by being earthed. This may happen safely by connecting them to the earth with a conductor.
Define an electric field as
the region where an electric charge experiences a force
Describe the shape and direction of the electric field around a point charge and between parallel plates and relate the strength of the field to the concentration of lines and how would we draw ts
We would have a circle with either a + or - in the middle to determine the charge
we would have lines going out the circle and if its + then there would be arrow lines pointing out and if its - then its arrows pointing in
If the charge is strong, we would need more lines
What is a uniform electric field and how do we draw it
When electric field between 2 parallel plates are all the same at all places
We draw it with 2 parallel plates (one positive one negative) and straight lines connecting each of the plates
How do we draw a positive and negative charge next to each other in an electric field
IF the positive charge is on the left and the neg is on the right, then you need a few lines facing left on the left side of the positive and same but right side for neg
For lines in the middle/facing the middle you need to connect them with curved lines, so both charges are connected. The arrow will be facing from the positive to the negative (search up if confused)
How do we draw a positive and positive (or neg and neg) charge in an electric field
For pos and pos:
For lines facing the middle, they would go in their normal direction and (if they are at the top facing the middle) will hook up and (if they are at the bottom facing the middle) hook downwards - sort of avoiding/repelling the other ones. The arrow symbols still point outwards
its the same for neg but the arrow symbols point inwards
Explain how the concept of an electric field helps to explain the
phenomena of static electricity
Electrons sit on the field lines proving static electricity exists
When lines of an electric field meet they produce a force. Like all forces this produces movement if the force is large enough to overcome the inertia of the charged particles.
