Static Electricity Flashcards
What are the two types of electricity?
Static and current
What is static electricity?
Electricity that involves ‘unmoving’ electrons.
When a body loses electrons…
…it becomes positively charged.
When a body gains electrons…
…it becomes negatively charged.
What is charge?
Denoted by Q or q, it is a quantity based on the number of electrons missing or present. It is a scalar quantity measured in coulombs (C).
How would you demonstrate repulsion and attraction of charges?
Use a perspex rod, while one is on a watch glass on oil and the others are charged perspex and polythene.
What is a conductor?
A medium that allows electric charge to flow through it easily.
What is an insulator?
A medium that does not allow electric charge to flow through it easily.
What does charging objects by induction mean?
When charging objects by induction, we cause materials to become charged by forcing the electrons to move a certain way.
How would you demonstrate the separation of charges in two insulated spheres? / How would you charge two insulated spheres by induction?
Place two insulated spheres in contact, hold a negatively charged rod near one of them, separate the spheres while keeping the rod in place, remove the rod.
How would you demonstrate the separation of charges in one insulated sphere? / How would you charge an insulated sphere by induction?
Hold a negatively charged rod near an insulated sphere, earth the sphere (by touching it), remove the earth and remove the rod.
What are uses of the gold leaf electroscope?
- To detect and identify charge
- To approximate the size of applied charge
- To test whether a material is an insulator or a conductor
How do electrons distribute themselves on a conductor in static electricity?
All static charge resides on the outside of a conductor (discovered by Faraday) and static charge tends to accumulate at the point of a conductor.
What are the only environments completely secure from lightning?
Faraday cages
What led to the invention of lightning rods and who invented them?
Knowledge about the accumulation of charge at a point, Benjamin Franklin.
What is the purpose of a Van de Graaff generator?
It is designed to generate and demonstrate effects of static electricity.
How does a Van de Graaff generator work?
- As the bell rotates, metal combs transfer charge to the metal dome. Charge spreads out equally on the outside of the dome. The more the bell rotates, the stronger the charge built up.
- If an earth is brought near the dome, a static discharge will ‘arc’ to it.
- If a person is in contact with the dome, they recieve the charge as it tries to go to earth. As hair is negatively charged, the electrons repel each other and the hair stands up.
How would you demonstrate that all static charge resides on the outside of a conductor?
Touch a proof plane on the outside of the dome and test with an electroscope to show it has gained charge. Earth it and repeat on the inside of the dome to show absence of charge.
How would you demonstrate that static charge tends to accumulate at a point?
Touch a pear shaped conductor to a charged Van de Graaff generator. Test the rounded and pointed side on a gold leag electroscope.
State Coulomb’s law.
The electrostatic force between two point charges is proportional to the product of their charges and inversely proportional to the square of the distance between them.
What is permittivity?
A measure of the ability of a material to resist the formation of an electric field within it. Measured in farads per metre
What are electric field lines?
They show the direction and strength of a force due to a positive charge in the field.
How would you demonstrate electric field lines?
Using magnets, paper and iron shavings.
What is electric field strength?
The force at any point in an electric field that a 1C charge would experience at that point.
