Static and Current Electricty Flashcards
What happens when two insulating materials are rubbed together?
Electrons will be scraped off one and dumped on another. Leaving a positive charge on one and a negative charge on the other.
What happens when polythene and acetate rods are rubbed with a cloth duster?
With the polythene rod, Electrons move from the duster to the rod and the rod becomes negatively charged and the duster is left with an equal opposite positive charge.
With the acetate rod, electrons move from the rod to the duster, duster becomes negatively charged and the rod becomes positive.
Two things with opposite charges will…
Two things with the same charges will…
attract
repel
Describe how clothing crackles can cause little sparks or shocks
Synthetic clothes are dragged over each other like in a tumble drier, and electrons get scraped off, leaving charges on both. This leads to inevitable attraction between the two and little sparks as the charges rearrange themselves.
Describe how car shocks can cause little sparks or shocks
Static charge can build up between your clothes and a synthetic car seat, the friction between the two causing electrons to scrap off, then when you touch metal as you exit the charge, current flows and so a shock is created.
Describe how door handles can cause little sparks or shocks
If you walk on a nylon carpet with shoes with insulating soles, there is a transfer of electrons and charge will build up on your body, then if you touch a metal door handle the charge flows to the conductor producing a shock
How can balloons stick to walls?
When you rub a balloon against your hair or clothes it becomes negatively charged as electrons are transferred to it. It sticks to the wall because charges on the wall can move a little, the negative charges on the balloon repel the negative charges on the wall, leaving positive charges on the surface, attracting the balloon and so it sticks.
What is the process of using a charged object to attract a non charged object called?
Induction
How is lightning caused by a build up of static electricity?
Rain drops and ice bump together inside storm clouds, knocking electrons off and leaving the top of the cloud positively charged and the bottom negatively, this creates a huge voltage and spark.
How do paint sprayers use electrostatic charges to get an even coat?
The spray gun is charged, which also charges the drops of paint, each has the same charge and so repel each other, giving a fine even spray. The opposite charge is given to the object to be painted, attracting the fine spray. Hardly any paint is wasted, also parts pointing away still receive paint so there are no paint shadows.
What other sprayers work the same as paint?
Insecticide
How can electrostatic charges cause complications in fuelling?
As fuel flows out of the filler pipe, friction can cause static to build up.
This can easily lead to a spark which could lead to an explosion, like when filling up a car at a petrol station.
How can problems with fuelling be solved?
By earthing
What is earthing?
Connecting a charged object to the ground using a conductor (e.g. copper wire)
This provides an easy route for the charges to travel to the ground instead of building up.
Electrons flow down the conductor if the charge is negative and flow up if the charge is positive.
Where is earthing used?
With fuel tankers to stop fuel exploding
What is an electric current?
The rate of flow of charge around a circuit
What is current carried by?
Electrons
Why are metals good conductors?
They have free electrons that can carry a charge
More charge passes around a circuit when…
A current flows
What is the formula for charge?
Charge (in coulombs) = current (A) x time (s)
What type of current do cells and batteries use?
DC
What is dc?
Direct Current - current only flows in one direction, as well as the charge
On an oscilloscope a direct current…
Always has the same voltage, and so is a straight line
Current will only flow through a component if…
there is a voltage across that component (A)
