Electrical quantities Flashcards
Two types of electrical charge
positive and negative
What happens when two meet
opposite attract
Like charges repel
Unit of charge
Coulombs (C)
Explain field patterns of charges
Electric charges create electric fields in the regions around them
The electric field is the region in which another charge will experience a force
Field lines go away from positive charges and towards negative charges
What is an electron
A negatively charged particle
Definition - conductor
a material that allows charge to flow through it
Definition - insulator
a material that does not allow the flow of charge through it
Examples of conductors
metals
graphite
Examples of insulators
plastics
glass
Explain - charging by induction
When a charged object is held close to a conductor, electrons in the conductor are able to move towards or away from the charged object
e.g. if electrons from a piece of aluminium foil are attracted to a +ve charged rod
This causes the top of the foil to become -ve charged whilst the bottom edge of it will be left with a positive charge
The attraction between the positive rod and the -ve charges on the top surface of the foil will cause the foil to be attracted to the rod
When does the flow of current occur
When two oppositely charged conductors are connected together
This is called an electric circuit
The greater the flow of charge, the greater the electric current
Equation of charge (current and time)
Q = IT Charge = current x time
How to measure current
Using an ammeter
Ammeters must be connected in series
How is current caused in metals
by a flow of free, delocalised electrons
Explain - conventional current
the flow of electrons from negative to positive (even though electrons go the other way
What is electromotive force
The name given to the potential difference of the power source in a circuit
The Electromotive force is measured in volts (V)
EMF of a power supply measured in volts is…
The amount of energy measured in joules supplied to each coulomb
Explain - Potential difference
As charge flows around a circuit, energy is transferred to or from the charge
The P.D. between two points in a circuit is related to the amount of energy transferred between those points in the circuit
P.D. is measured in volts (V)
1 volt is equal to
1 joule per coulomb (J/c)
How to measure potential difference
Using a voltmeter
It must be connected in parallel with the part if the circuit being measured
What is resistance
The opposition to current
The greater the resistance the lower the current
What is the unit of resistance
Ohm
Equation of resistance
R=V/I
Factors affecting resistance of a wire
The longer the wire = greater resistance - the electrons will collide with more ions creating greater resistance
The thicker the wire = smaller resistance - the more space there is for the electrons so more electrons can flow
What happens to resistance if the length is doubled
the resistance is doubled
The resistance of a wire is proportional to its length
What happens to resistance if the cross-sectional area is doubled
Resistance is halved
The resistance of a wire is inversely proportional to its cross sectional area
Describe the IV graph for a reistor
The current is proportional to voltage
Describe the IV graph for a filament lamp
The current increases at a proportionally slower rate than the potential difference
this is because -
The current causes the filament in the lamp to heat up
As the filament gets hot its resistance increases
This opposes the current, causing it to increase at a slower rate
What happens as electricity is passed around the circuit
Energy is transferred from power source to various components
In the components it loses energy in light, heat energy
Equation connecting energy transferred current time and potential difference
E = IVT
Energy transferred = Current x Voltage x Time
Equation for electrical power (watts)
P = IV Power = Current x time
