3.5 Electricity
3.5.1 Current Electricity
3.5.1.1 Basics of Electricity
Definitions
● Current - the rate of flow of charge
● Potential Difference - the work done per unit charge
● Resistance - the energy per unit charge lost per unit current
● Series - single path for current to take
● Parallel - multiple paths for current to take
● Power - work done per unit time
● Energy - the ability to do work
● Charge - intrinsic fundamental property of matter (can be +ve or -ve)
Equations
● P = I2R, P = IV, P = E/T, P = V2/R
● V = IR
● R1 + R2 …
= RT for series (reciprocal for parallel)
● Q = IT
● V = E/Q
● I = Q/T
● Current into junction = current out of junction
3.5.1.2 Current-Voltage Characteristics
Ohm’s Law
● V = IR → always true for an instantaneous reading
● V directly proportional to current → V=kI (k = resistance)
● True for OHMIC CONDUCTOR - ohmic conductors have constant resistance
, Common Current-Voltage Characteristics
Diode Filament Lamp Resistor
Ideal Values
● Ammeter → zero resistance
● Voltmeter → infinite resistance
3.5.1.3 Resistivity
● Resistance is directly proportional to length
● Resistance is inversely proportional to area
● Ⲣ (ro) = RA/L
● Ⲣ = resistivity (measured in Ωm)
● R = resistance (measured in Ω)
● A = cross-sectional area (measured in m2)
● L = length (measured in m)
Thermistors
The resistance of a thermistor decreases as temperature increases as more
charge carriers (electrons) are available at higher temperatures.
Light Dependent Resistors (LDRs)
The resistance of an LDR decreases as light intensity increases. This is because
there are more electrons at available light levels.
Superconductors
Superconductors are materials that can conduct electricity with negligible
resistance, meaning no energy is wasted (either in the form of heat or sound or a
similar form) when charge flows through the material. Due to the laws of physics,
3.5.1 Current Electricity
3.5.1.1 Basics of Electricity
Definitions
● Current - the rate of flow of charge
● Potential Difference - the work done per unit charge
● Resistance - the energy per unit charge lost per unit current
● Series - single path for current to take
● Parallel - multiple paths for current to take
● Power - work done per unit time
● Energy - the ability to do work
● Charge - intrinsic fundamental property of matter (can be +ve or -ve)
Equations
● P = I2R, P = IV, P = E/T, P = V2/R
● V = IR
● R1 + R2 …
= RT for series (reciprocal for parallel)
● Q = IT
● V = E/Q
● I = Q/T
● Current into junction = current out of junction
3.5.1.2 Current-Voltage Characteristics
Ohm’s Law
● V = IR → always true for an instantaneous reading
● V directly proportional to current → V=kI (k = resistance)
● True for OHMIC CONDUCTOR - ohmic conductors have constant resistance
, Common Current-Voltage Characteristics
Diode Filament Lamp Resistor
Ideal Values
● Ammeter → zero resistance
● Voltmeter → infinite resistance
3.5.1.3 Resistivity
● Resistance is directly proportional to length
● Resistance is inversely proportional to area
● Ⲣ (ro) = RA/L
● Ⲣ = resistivity (measured in Ωm)
● R = resistance (measured in Ω)
● A = cross-sectional area (measured in m2)
● L = length (measured in m)
Thermistors
The resistance of a thermistor decreases as temperature increases as more
charge carriers (electrons) are available at higher temperatures.
Light Dependent Resistors (LDRs)
The resistance of an LDR decreases as light intensity increases. This is because
there are more electrons at available light levels.
Superconductors
Superconductors are materials that can conduct electricity with negligible
resistance, meaning no energy is wasted (either in the form of heat or sound or a
similar form) when charge flows through the material. Due to the laws of physics,
