How does static build up?
When certain insulating materials are rubbed together, negatively charged electrons will come off one and onto the other. These electrons are not free to move, so it is static. One has a positive static charge and one has an equal negative charge.
How can electrically charged objects attract uncharged objects?
Charges can move a little. This means a charged object will repel the like charges on the other object. As different charges attract, the two objects are attracted to each other. This is called charging by induction.
What causes sparks?
As electric charge builds on an object, the potential difference between the object and the earth (0V) increases. If this gets large enough, electrons can jump across the gap, causing a spark. They can also jump onto nearby earthed conductors e.g. humans.
How is static electricity used in electrostatic sprayers?
The spray gun is charged, charging the drops of paint. This means they repel each other, giving a fine, even spray. The object is given the opposite charge, attracting the paint all over.
How can static electricity be dangerous?
Refuelling cars - fuel can build up static as it flows out of a pipe. This can lead to a spark, causing an explosion.
Static on airplanes - friction between the air and the plane can charge it. This can interfere with communication equipment.
Lightning - raindrops and ice bumping together leaves some of the cloud positively charged and some negatively. This creates a spark.
How does earthing work?
Connect a charged object to the ground using a conductor. This provides an easy route for static charges to travel into the ground, so none can build up to make a spark.
What are electric fields like?
They are created around electrically charged object. If a second charged object is placed inside it, a force would be exerted on both. The closer to the object you get, the stronger the field is. They can be shown using field lines.
What causes electrostatic forces?
Electric fields: when a charged object is placed in an electric field, it feels a force. This is caused by electric fields around two interacting objects. If the field lines point in the same direction, field lines join up and they are attracted. If they point in opposite directions, they push against each other and they repel.
What is the field like between two oppositely charged parallel plates?
It is uniform - the strength and direction of the field is the same anywhere between the two plates. It is curved slightly at the ends.
How does sparking work?
A statically charged object generates is own electric field. This then interacts with other electric fields. A high potential difference causes a strong electric field between the charged and earthed object. This causes electrons in the air particles to be removes (ionisation). This causes air to become much more conductive, so a current can flow (the spark).