Static Electricity Flashcards
All 27 cards in this deck
When two insulators are rubbed together, which particles move?
Electrons only — protons never move.
What are the steps to explain how rubbing charges an insulator?
e.g. rubbing a plastic comb with a dry cloth so the comb becomes positive- Friction between the two materials.
- Electrons are transferred from the comb onto the cloth.
- The cloth gains electrons so is negative; the comb is left with an equal positive charge.
What charge is left on a material that loses electrons by friction?
Positive, and equal in size to the negative charge gained by the other material.
True or false? When you rub a balloon on a jumper, protons move from the jumper to the balloon.
False. Only electrons are transferred; protons stay fixed in the nuclei.
State the rule for the force between two electric charges.
Like charges repel; unlike charges attract.
True or false? Two spheres that are both given a negative charge will attract each other.
False. Like charges repel, so the spheres push each other apart.
Why can you get an electric shock when you touch a metal car door after getting out of a car?
Friction between your clothes and the seat transfers electrons, leaving you charged; touching the metal lets electrons move suddenly, giving a shock.
True or false? Static charge builds up on insulators because the charge cannot flow away through them.
True. Insulators do not conduct, so transferred electrons stay where they are.
How does a thundercloud become charged?
Ice and water particles rub together inside the cloud and transfer electrons, so the base of the cloud becomes negatively charged.
In terms of electrons, what is a lightning strike?
A discharge — the charge becomes large enough for electrons to jump from the cloud base to earth through the ionised air.
What are the steps to explain attraction by induction?
e.g. a positively charged comb picking up small pieces of paper- The charge on the comb attracts electrons in the paper towards it.
- A negative charge is induced on the part of the paper nearest the comb.
- Opposite charges attract, so the paper is pulled up to the comb.
True or false? A charged balloon can only stick to a wall if the wall is also charged.
False. The wall is uncharged; the balloon induces an opposite charge on its surface, so they attract.
Why are the paint or insecticide droplets from a sprayer all given the same charge?
They repel each other, so the spray spreads out into a wider, finer, more even cloud.
True or false? A sprayer gives paint droplets a positive charge by adding protons to them.
False. It removes electrons from the droplets; protons are never transferred.
Why is static electricity dangerous when refuelling a car or aircraft?
Friction as fuel flows charges the pipe and vehicle; a spark from the discharge could ignite the fuel vapour.
How does earthing a fuel tanker prevent an explosion?
A metal conductor to earth lets electrons flow to or from the ground, so charge cannot build up and spark.
True or false? Earthing removes excess positive charge by letting protons flow away into the earth.
False. Electrons flow from the earth onto the object to cancel the positive charge.
Define an electric field.
A region where an electric charge experiences a force.
Describe the shape and direction of the electric field around a positive point charge.
Straight radial lines spread out evenly all round it, with arrows pointing away from the charge.
True or false? The field lines around a negative point charge point outwards, away from the charge.
False. They are radial but point inwards, towards the negative charge.
Describe the electric field between two parallel charged plates.
Straight, equally spaced parallel lines (a uniform field), arrowed from the positive plate to the negative plate.
What does the arrow on an electric field line show?
The direction of the force on a positive charge placed at that point.
How is the strength of an electric field shown by its field lines?
The closer together the lines, the stronger the field.
Using fields, why do two charged spheres near each other experience a force?
Each sphere has an electric field, and the other sphere sits in that field, so it feels a force.
In terms of electric fields, why does a spark jump across an air gap?
The field between the charges becomes strong enough to ionise the air, so it conducts and electrons jump across.
True or false? An uncharged object placed in an electric field cannot experience any force.
False. The field moves electrons within it, inducing opposite charge on the near side, so it is attracted.
How does the electric field of a charged object explain induction in a nearby neutral object?
The field makes electrons in the neutral object move, leaving an opposite charge on the side nearest, which is then attracted.