Electrical Quantities Chapter Notes | Physics for GCSE/IGCSE - Year 11 PDF Download

 Page 1


Electrical quantities
? Conductors
? The materials that can pass electricity through them easily
? Free electrons are present in conductors
? E.g. metals ? silver, copper etc.
? Insulators
? The materials that cannot pass electricity through them
? Free electrons are absent
? E.g. wood, rubber, plastics etc.
? Electric current
? It is the flow of charge through a conductor
? Electric current = charge / time
? I = Q / t
? S.I unit of electric current is Ampere (A)
? 1 ampere = 1 coulomb / 1 second
? Ammeter
? An instrument used to measure electric current
? 1 milliamp = 1 mA = 1/1000 Ampere (.001 or 10^-3)
? 1 microamp = 1 nA = 10^-6 Ampere
? Electric circuit
? A closed path in which an electric current flows
? Types of current
? Conventional current
¦ Positive to negative
? Electronic current
¦ Negative to positive
? Electromotive force
? An electrical supply (a power pack, cell or battery) provides electrical energy which drives
charge around a complete circuit
? The electromotive force of a supply is the energy provided per coulomb of charge and is
measured in volts
? Combining electromotive force
? E = E1 + E2 + E3
? V = W / Q
? Volts / EMF = Work (energy) / Charge in coulombs
? Voltmeter
? A device that is used to measure the voltage / potential difference
? Voltmeter is always connected
Page 2


Electrical quantities
? Conductors
? The materials that can pass electricity through them easily
? Free electrons are present in conductors
? E.g. metals ? silver, copper etc.
? Insulators
? The materials that cannot pass electricity through them
? Free electrons are absent
? E.g. wood, rubber, plastics etc.
? Electric current
? It is the flow of charge through a conductor
? Electric current = charge / time
? I = Q / t
? S.I unit of electric current is Ampere (A)
? 1 ampere = 1 coulomb / 1 second
? Ammeter
? An instrument used to measure electric current
? 1 milliamp = 1 mA = 1/1000 Ampere (.001 or 10^-3)
? 1 microamp = 1 nA = 10^-6 Ampere
? Electric circuit
? A closed path in which an electric current flows
? Types of current
? Conventional current
¦ Positive to negative
? Electronic current
¦ Negative to positive
? Electromotive force
? An electrical supply (a power pack, cell or battery) provides electrical energy which drives
charge around a complete circuit
? The electromotive force of a supply is the energy provided per coulomb of charge and is
measured in volts
? Combining electromotive force
? E = E1 + E2 + E3
? V = W / Q
? Volts / EMF = Work (energy) / Charge in coulombs
? Voltmeter
? A device that is used to measure the voltage / potential difference
? Voltmeter is always connected
? Potential difference
? The potential difference or voltage across a component in a circuit is the energy required per
coulomb of charge to drive the current through that component
? It is the amount of electrical energy converted into other forms per coulomb of charge
? It is measured in volts
? Potential difference = work/Charge (C)
? 1 volt = 1 joule / coulomb
? Ohm’s law
? The current flowing through a wire is proportional to the potential difference across it provided
the temperature remains constant
? Resistance
? The electrical resistance of an object is a measure of its opposition to its opposition to the flow
? Resistance is measured in ohms (O)
? Resistance = Potential difference (V) / Current (A)
? Current is directly proportional to the voltage
Factors affecting resistance
? Length of the conductor (L)
? Resistance of the conductor is directly proportional to the length of the conductor
? Area of cross-section of the conductor (A)
? Resistance of the conductor is inversely proportional to the area of the cross-section
? Temperature (T)
? Resistance of the conductor is directly proportional to the temperature
? Nature of the material
? Copper has lower resistance than iron, the more conductive it is, the lesser resistance
? Resistivity
? It is the property of a material that measures how strongly it resists the flow of electric
current
? Resistivity = (Resistance x area) / Length
? SI unit of resistivity is Om, Ohm meter
? The resistor follows ohm's law therefore is a
ohmic resistor
? The filament lamp is not constant and
proportional therefore does not obey the ohm's
law therefore is a non-ohmic conductor
Page 3


Electrical quantities
? Conductors
? The materials that can pass electricity through them easily
? Free electrons are present in conductors
? E.g. metals ? silver, copper etc.
? Insulators
? The materials that cannot pass electricity through them
? Free electrons are absent
? E.g. wood, rubber, plastics etc.
? Electric current
? It is the flow of charge through a conductor
? Electric current = charge / time
? I = Q / t
? S.I unit of electric current is Ampere (A)
? 1 ampere = 1 coulomb / 1 second
? Ammeter
? An instrument used to measure electric current
? 1 milliamp = 1 mA = 1/1000 Ampere (.001 or 10^-3)
? 1 microamp = 1 nA = 10^-6 Ampere
? Electric circuit
? A closed path in which an electric current flows
? Types of current
? Conventional current
¦ Positive to negative
? Electronic current
¦ Negative to positive
? Electromotive force
? An electrical supply (a power pack, cell or battery) provides electrical energy which drives
charge around a complete circuit
? The electromotive force of a supply is the energy provided per coulomb of charge and is
measured in volts
? Combining electromotive force
? E = E1 + E2 + E3
? V = W / Q
? Volts / EMF = Work (energy) / Charge in coulombs
? Voltmeter
? A device that is used to measure the voltage / potential difference
? Voltmeter is always connected
? Potential difference
? The potential difference or voltage across a component in a circuit is the energy required per
coulomb of charge to drive the current through that component
? It is the amount of electrical energy converted into other forms per coulomb of charge
? It is measured in volts
? Potential difference = work/Charge (C)
? 1 volt = 1 joule / coulomb
? Ohm’s law
? The current flowing through a wire is proportional to the potential difference across it provided
the temperature remains constant
? Resistance
? The electrical resistance of an object is a measure of its opposition to its opposition to the flow
? Resistance is measured in ohms (O)
? Resistance = Potential difference (V) / Current (A)
? Current is directly proportional to the voltage
Factors affecting resistance
? Length of the conductor (L)
? Resistance of the conductor is directly proportional to the length of the conductor
? Area of cross-section of the conductor (A)
? Resistance of the conductor is inversely proportional to the area of the cross-section
? Temperature (T)
? Resistance of the conductor is directly proportional to the temperature
? Nature of the material
? Copper has lower resistance than iron, the more conductive it is, the lesser resistance
? Resistivity
? It is the property of a material that measures how strongly it resists the flow of electric
current
? Resistivity = (Resistance x area) / Length
? SI unit of resistivity is Om, Ohm meter
? The resistor follows ohm's law therefore is a
ohmic resistor
? The filament lamp is not constant and
proportional therefore does not obey the ohm's
law therefore is a non-ohmic conductor
? Electrical power
? It is the rate at which energy is transferred from one place to another place or
transferred from one form to another
? Electrical power = Energy transformed / time taken
? Electrical power = Current x voltage
? SI unit of electrical power is Watt (W)
? The amount of electrical energy used by a component depends on 3 things
? The current
? The potential difference
? The amount of time the device is used for
? Energy transferred
? Current x voltage x time  ( I x V x t)
? Power x time  (P x t)