Chapter 8 (8.1 - 8.7) Electricity Flashcards
what is an electric charge
a property of matter that experiences a force when next to other charges or in an electric field.
when do masses attract
when they are of opposite charge
when do masses repel
when they are of same charge
what is a conductor
do they hold charge?
Materials that let electrons pass through them and have free electrons to carry charge.
Do not hold their charge
Materials that are conductors
2 examples
Metals - good conductors
Non-metals - poor conductors or don’t conduct at all. Except carbon
copper, iron
What is an insulator
easy method to charge
2 examples
Materials that can hardly conduct. Electrons are held to atoms tightly.
Can be charged easily via friction since aft electrons are transferred they stay there. That’s why they hold their charge.
Glass, rubber
What are semi conductors
Materials that are bad conductors when cold but good conductors when hot
What is earthing?
if its negatively charged?
if its positively charged?
process of neutralizing an object’s charge by connecting it to the earth and letting electrons flow in or out.
if -ve charge: excess electrons in the object flow to the earth
if +ve charge: electrons flow from the earth to the object
When is an object positively/negatively charged
When neg charges > positive
negatively charged
vice versa
Process of induction (giving an object a negative charge)
- get a positively charged rod near the object
- charges are separated - the electrons are attracted and protons are repelled
- connect an earthing wire - electrons flow into the object to neutralize the protons
- disconnect earthing wire
- take the positively charged rod away from the object
- now the sphere has more electrons than protons hence it has a negative charge now,
What is the SI unit of Charge
symbol
Coulomb (C)
what is an electrical field
region where charged particles experience a force. one charged particle will experience force from the other
Direction of electric field of a positive charge
Radially outward
Direction of electric field of a negative charge
Radially inward
How does charging by friction occur
When 2 objects are rubbed together, heat is generated. This heat energy gives the electrons enough energy to overcome their bond energies that are holding them to the atoms and allow them to travel to the other object.
The electrons and protons are no longer equal hence one object is +ve nad one is -ve
Charge of 1 electron
-1.6 * 10^-19 C
Charge of 1 proton
1.6 * 10^-19 C
Direction of electric field lines between 2 oppositely charged plates that are parallel to eachother
If the distance between plates is shorter compared to the length of the plate the curves of the electric fields on the edges reduces.
what is current
notation and SI unit
formula with respect to charge
rate of flow of charge
charge/time=Q/T=coulumb/time
notation = I
SI unit = Ampere
What is used to measure current
how is it connected
a special characteristic of it
Ammeter
Connected in series
Ideal ammeter - has 0 resistance
How does current vary in a series circuit
it remains constant
what is conventional current
is the flow of current from a positive terminal to negative
what is potential difference
unit and formula with respect to charge
work done per unit charge
Volt (V)
V = W/Q where W = work done, Q = charge
What is EMF
when is it the highest
Electromotive Force -
Amount of force/work done required to move a charge across the whole circuit.
The maximum potential difference
Highest when a battery is not connected to a circuit so p.d doesn’t drop.
Formula for EMF
Sum of potential diff of all components in circuit
What is used to measure voltage
how is it connected
special characteristic
Using a voltmeter
Connected in parallel
Ideal voltmeter - infinite resistance
what is the definition of resistance and S.I unit
opposes the flow of current. Doesnt allow current to move freely
S.I unit is ohms
what is ohms law
V = IR
v = potential diff
I = current
R = Resistance
what are the factors affecting resistance
length
thickness of wire
temperature
material
how does length affect resistivity
longer the wire greater the resistance
(directly proportional)
how does thickness of the wire affect resistance
inversely proportional to the resistance.
thicker the wire lesser the resistance, as there are more particles for electricity to be conducted
how does temperature affect the resistance
as temperature increases resistance increases in conductors
as temperature increases resistance decreases in semiconductors
how does material affect the resistance
notation
as some materials help conduct the charge and others don’t conduct the charges as well.
notation: symbol rho - ρ
Relation of resistance to the factors (formula)
resistance = resistivity x length/area
What is a thermistor
give a use
Components that have high resistance when cold but low resistance when hot. Made of semiconductor materials
smoke detectors, thermostats
what are some factors of ohms law
as voltage increases, resistance increases
how would a graph between voltage and current look when resistance is constant
straight line
how would a graph between voltage and current look when resistance is changing
curved
in parallel circuit what happens to voltage and current
voltage is same
current differs
how are the field lines of a positively charged particle drawn
arrows pointing outward from the particle
how are the field lines of an negatively charged particle drawn
arrows pointing towards the object from the outside
explain why energy losses are lower when voltage is higher
higher voltage = lower current (in power law/P=VI)
if current is lower then less energy is produced (E= VIT)
if less energy produced then less energy will be lost
e.m.f definition
the total energy needed to transfer the charges from one terminal of the battery to the other
in a series circuit what happens to voltage and current
current is same
voltage differs
