Electricity Flashcards
Charge: Key points
-Charge is a property that objects can have…it is fundamental
-Charge can be positive or negative
-Charge is measured in coulombs (C)
-Insulators prevent charge from moving (Most non-metals)
-Conductors allow charge to move ( metals and graphite). They have “delocalized” electrons
-Electrons are usually responsible for movement of charge (current). They have a very small charge
-1.6 x 10^-19
Charging by friction
-When two insulators are rubbed together, ELCTRONS are transferred from one to the other and the objects become charged
-This called charging by friction because friction is the force that moves the electrons
-Only electrons move
-POSITIVE CHARGE DOESN’T MOVE
Why can’t positive charge move?
Electrons are free to move from their electron shells. Protons are bound in the nucleus so they can’t move.
Why can metals conduct electrical charge?
Metals conduct electricity well because the delocalized electrons in the metallic lattice structure are “free” to carry charge whereas in insulators the electrons are “bound”.
Many insulators are made of non metals where the electrons are “bound” in place, unable to carry the charge.
What is electron affinity?
Some materials “hold onto” electrons better than others. When two different insulators are rubbed together, one will have a greater “affinity” for electrons. Friction will transfer electrons from the material with the least affinity, to the one with the most.
Classic question: When rubbed with a cloth one end of a rod gains a negative charge. What charge does the other end gain?
Neutral. No charge flows down the rod as it is an insulator.
What is a triboelectric series?
A triboelectric series is a listing of a variety of insulators in order of their relative attraction for the electrons of another material
You will always be told which end is positive and which is negative- your first step should be to always check which end is which.
Materials closer to the positive end LOSE electrons to the material closest to the negative end.
What is charging by induction?
When a charged object is moved to a neutral object, the electrons are either transferred or repelled by the charged object, giving the neutral object are positive or negative charge.
-A charged object can be attracted to a neutral object if it comes close enough to move the electrons in the neutral object: this is charging by induction
What is an electric field?
An electric field is a region in which an electric charge experiences a force. The direction of the field is direction in which a positive test charge would move.
What does the arrow mean in the field lines?
The arrows show the direction a positive charge would feel a force in the field. A negative feels a force in the opposite to the arrow
What direction does a charge flow?
From positive to negative.
Why do the girl’s hair stand on end when touching the van de graff generator?
Positive charges are flowing through her body and since her hair is positively charged. it is repelled by the body and the hairs stand on end
Why does she stand on a plastic stool?
Plastic is an insulator. It stops the charge going to Earth. If she stands on the ground her hair will go down
What are some uses of static electricity?
-Removing pollutants in power stations
-Car spraying and painting
What are some dangers of static electricity?
Fuel fires, sparks near powders, lightning
What is current?
-Current is the rate at which charge (coulombs) passes a point in a circuit
-Current is measured with an ammeter in a circuit which is placed in series at the point where the current needs to be measured
I=Q/t
Charge (Q) must be given in coulombs, current (I) in amps and time (t) in seconds
What is conventional current?
-The direction positive charges would flow in a circuit
What is the flow of electrons in a circuit?
The flow of electrons is from negative to positive in a circuit.
How do you represent a negative charge in a diagram and the force it experiences?
e- and an arrow for the force
IN a battery symbol which line is positive and negative
Longer line represents the positive terminal of the cell/battery and the shorter, sometimes bolder line is the negative terminal
What is current?
current is the rate of flow of charge in a circuit
What is a voltmeter?
A voltmeter is an instrument used for measuring a voltage difference or POTENTIAL DIFFERENCE between two points in an electrical circuit
-A voltmeter is connected in parallel with a component to measure its voltage so that the voltmeter doesn’t affect the circuit, it must not take any current so it must have infinite resistance
-If we use a voltmeter across a cell, we are not measuring energy used, we are measuring energy available. We call this measurement the EMF … electromotive force.
What is the potential difference (p.d) ?
-The potential difference is a measure of how much energy is being used by each coulomb of charge flowing between the two points
-Difference in Electrical Energy per unit charge converted to other forms of energy between two points in a circuit
What is electromotive force?
Energy provided by an energy source per unit charge
What is voltage?
The joules of energy available per coulomb of charge. The pressure that pushes on the electrons.
What kills, current or charge?
The current is how much charge is hitting you per second.
What is resistance?
Resistance is the opposition to the flow of current in a circuit( measured in ohms)
What causes resistance?
When electrons are moving through a wire, atoms are vibrating and getting the way so this causes collisions between atoms and electrons which causes heat and resists the flow of charge.
