Electrostatics Flashcards
Two kinds of charge
State that:
- all materials contain positive charges (protons) and negative charges (electrons)
- An object that has an equal number of electrons and protons is neutral (no net charge)
- positively charged objects are electron deficient
- negatively charged objects have an excess of electrons
How are objects (insulators) charged?
Through contact / rubbing
TRIBO-ELECTRIC CHARGING
Define Tribo-electric charging
A type of contact electrification in which certain materials become electrically charged after they come into contact with different materials and are then separated (such as through rubbing)
* the Polarity & Strength of the charges produced- differ according to materials.
Forces exerted on each other: principle
Like charges repel
Opposite charges attract
How do charged objects attract uncharged insulators?
Through the polarisation of molecules inside insulators
Define Polarisation
The partial or complete polar separation of positive and negative electric charge in a system.
Why do neutral particles become attracted to charged objects?
Neutral particles have no overall charges( but contain protons & neutrons within)
*The electric field from the charged object causes a slight rearrangement of the charges within the neutral particle. It develops a temporary separation of charge:
*one side slightly more POSITIVE
*the other side more NEGATIVE
this results in attraction of the induced dipole
What is SI?
International system of units
SI unit for electric charge (Q):
Coulomb (C)
State the:
Principle of Conservation of Charge
The net charge of an isolated system remains constant during any physical process.
(Eg) two charges making contact then separating)
Formula:
Calculating net charge for two or more objects in isolated system
Qnet=Q1+Q2
When two identical conducting objects having charges Q1 and Q2 on insulating stands touch…
Each object has the same final charge on separation
Final charge after separation:
Q = (Q1 + Q2) / 2
Final charge after separation formula only true for…
Identically sized conductors on insulated stands
Calculate change in charge that occurred for an object in an isolated system during contact with another identically sized object
Q(transferred) = Q(final) - Q(initial)
What does a positive (change in charge) answer indicate?
The object’s charge INCREASED
*this takes place when electrons are LOST
What does a negative answer indicate?
The object’s charge DECREASED
* electrons are GAINED
Principle of charge quantisation
All charges in the universe consist of an integer multiple of the charge on one electron.
Q = nq
q = 1.6 x 10 ^-19 C (pos= protons / neg = electrons)
n = integer
Calculating net charge of an isolated system
Qnet = Q(a) + Q(b) (+)…..
Calculating new charge on each sphere after they made contact and were separated
(Q after separation)
Q(final) = Qnet / number of spheres
(Qa + Qb) / 2
Calculating new charge on each sphere after they made contact and were separated
(Q after separation)
Q(final) = Qnet / number of spheres
(Qa + Qb) / 2
Calculating charge that has been transferred from one sphere to another
ΔQ = Q(final) - Q(initial)
(This becomes the magnitude of the charge of the electrons transferred = Q(transferred)
Calculating the number of electrons transferred from one sphere to another to another / (electrons in excess)
n = Q/ q e-
