Section 6 - Electricity Flashcards
Current def
Rate of flow of charge
I, Q, T formula
Q = It
Direction of current flow
+ to -
Unit of charge
Coulomb (C)
Coulomb def
One coulomb is the amount of Charge that passes in 1 second if the charge is 1 Amp
Potential Difference def
Work done per unit charge moved
Voltage f
v = W/Q (Word done/charge)
Voltage in components connected in a parallel
The same
Current in components connected in a parallel
Shared
Voltage in components conected in series
Shared
Current in components connected in seres
The same
How must a voltmeter be connected
in parallel with the component
Definition of a volt
1 volt is when you convert 1 joule of energy moving 1 coulomb of charge through a component
Resistance f
R = V/I
Resistance def
A measure of how difficult it is for current to flow through a component
Ohmic conductor def
A conductor for which |R is constant
Ohms law
Provided the physical conditions, such as temperature, remain constant, the current through an ohmic conductor is directly proportional to the current across it
Graph for an ohmic conductor
Straight line graph passing through (0,0)
Circuit to obtain an I/V graph
INsert pic
I/V graph for a filament lamp
INsert pic
I/V characteristic for a filament lamp
The resistance of a metal increases as the temperature increases
Semiconductors
Thermistor def
A resistor with a resistance that depends on temperature
NTC thermistor
Negative temperature coefficient
Resistance decreases as temperature goes up
Filament lamp symbol
Pic
Thermistor symbol
Pic
NTC thermistor I/V graph
Pic
How a NTC thermistor works
Warming the thermistor gives more electrons enough energy to escape from their atoms, this means that there are more charge carriers available so the resistance is lower`
Diodes def
Components that only allow current to flow in one direction
Diode Symbol
Pic
LED symbol
Pic
Forward bias def
The direction in which a diode allows current to flow
Three things that determine resistance
- Length of wire (l)
- Cross sectional area of a wire (A)
- Resistivity ((P))
Resistivity def
The resistivity of a material is defined as the resistance of a 1m length with corss sectional area 1m^2
Resistivity units
Ohm-metres`
Resistivity formula
RA/l
Experiment to find the resistivity of a wire
Superconductors def
Materials with zero resistance
Power def
The rate of transfer of energy
Unit of power + def
Watts: 1 joule per second
Power formla
P = E/t
3 formulae for power in a electrical circuit
P = VI
P = (v^2)/R
P = (I^2)R
What causes resistance
Resistance comes from electrons colliding with atoms and losing energy to other forms
Internal resistance def
The resistance to the flow of charge within a power source such as a battery
Load resistance
The total resistance of all components in the external circuit
EMF def
The amount of electrical energy the battery produces for each collumb of chargeE
EMF full form
Electromotive Force
EMF unit
VOlts
EMF formula
EMF = E/Q
Terminal PD def
The potential difference across the load resistance, the energy transferred when one coulomb f charge flows through the load resistance
What would happen if there was no internal resistance
The terminal PD would be the same as the EMF
Lost volts def
The energy wasted per coulomb overcoming the internal resistance
Conservation energy
Energy per coulomb supplied by the source
=
Energy per coulomb transferred in load resistance
+
Energy per coulomb wasted in internal resistance
4 formulae with EMF and internal resistance
Pic
EMF of cells in series
Et = E1 + E2 +E3 …
EMF of cells in parallel
Et = E1 = E2 = E3 …
Investigating Internal resistance and EMF circuit
Pic
Investigating internal resistance and EMF steps [3]
- Vary the current in the circuit by changing the vaue of theload resistance(using the variable resistor).
- Measure the PD for several values of current
- Record the results and plot a graph of v against I
Calculating internal resistance and MEF from a V-I graph
Pic
Kirchhoff’s fist law
Conservation of charge
The total current entering a junction = the total current leaving it
Kirchhoff’s second law
Conservation of energy
The total EMF around a series circuit = the sum of the PDs across each component
Adding resistance in series
Rt = R1 + R2 +R3 …
Deriving how resistance is added in series
Pic
Adding resistance in Parallel
1/Rt = 1/R1 + 1/R2 + 1/R3 …
Deriving how resistance is added in series
Pic
