OCR A-Level Physics Paper 2
Study
What is a charge carrier?
A charged particle capable of transferring electric current.
What do we mean when we say charge is quantised?
It can only take certain values (always ne)
If n electrons are removed from a neutral object what is its charge?
ne
What is an electrolyte?
A liquid containing charged ions.
What is a metallic conductor?
A material comprising a lattice of positive ions and delocalised electrons that carry
electrical current
Which direction does conventional current flow?
From positive to negative.
Which direction do electrons flow in a circuit?
From negative to positive.
What is an ion?
A non-neutral atom or molecule.
What is a cation?
A positively charged ion
What is an anion?
A negatively charged ion.
What is an anode?
A positive electrode.
What is a cathode?
A negative electrode.
How is an ammeter connected?
In series
What is the resistance of an ideal ammeter?
Zero.
State Kirchoff's first law.
At any point in a circuit the sum of the currents entering that point is equal to sum of the
currents leaving.
What is n in the equation I = nAve and what are its units?
Number density of free charge carriers m⁻³
What is A in the equation I = nAve?
Cross-sectional area of the conductor.
What is e in the equation I = nAve?
The elementary charge (1.6x10⁻¹⁹C)
What is v in the equation I = nAve?
The drift velocity of the charge carriers.
What is a conductor?
A material with a large number density of charge carriers ~10²⁸m⁻³
What is an insulator?
A material with a low number density of charge carriers.
, What is a semiconductor?
A material with an intermediate number density of charge carriers ~10¹⁷m⁻³
What is potential difference?
The work done per unit charge between two points
What is the SI unit for potential difference?
Volt (V)
What units are equivalent to the volt?
Joules per Coulomb (JC⁻¹ )
What is EMF (Electromotive force)?
The work done per unit charge supplied to the charge carriers
How is a voltmeter connected?
In parallel.
What is the resistance of an ideal voltmeter?
Infinite.
What is thermionic emission?
The emission of electrons from the surface of a heated metal.
What is the work done on an electron when it passes through a p.d. of V volts?
eV where e is the charge on the electron.
What is Ohm's Law?
For a metallic conductor at constant temperature the p.d. is proportional to current.
What is electrical resistance?
The opposition of an object to a flow of current through it.
How is resistance calculated?
V/I
What units are equivalent to an Ohm?
VA⁻¹
Why does resistance increases with temperature?
The amplitude of lattice ion vibrations increases causing more frequent collisions
between electrons and lattice ions, leading to the electrons doing more work as they
move through the wire.
Why does current flow lead to heating in components?
Electrons collide with the lattice ions and transfer some of their kinetic energy to the
lattice ion's vibrations.
What is an Ohmic conductor?
An object for which p.d. is proportional to current.
What is meant by the threshold pd of a diode?
The pd at which resistance starts to fall rapidly as pd increases.
What are the units of resistivity?
Ωm
What is ρ in R = ρL / A?
The resitivity of the material.
What is L in R = ρL / A?
The length of the wire.
What is A in R = ρL / A?
The cross-sectional area of the wire
As a metal gets hotter what happens to its resitivity?
Study
What is a charge carrier?
A charged particle capable of transferring electric current.
What do we mean when we say charge is quantised?
It can only take certain values (always ne)
If n electrons are removed from a neutral object what is its charge?
ne
What is an electrolyte?
A liquid containing charged ions.
What is a metallic conductor?
A material comprising a lattice of positive ions and delocalised electrons that carry
electrical current
Which direction does conventional current flow?
From positive to negative.
Which direction do electrons flow in a circuit?
From negative to positive.
What is an ion?
A non-neutral atom or molecule.
What is a cation?
A positively charged ion
What is an anion?
A negatively charged ion.
What is an anode?
A positive electrode.
What is a cathode?
A negative electrode.
How is an ammeter connected?
In series
What is the resistance of an ideal ammeter?
Zero.
State Kirchoff's first law.
At any point in a circuit the sum of the currents entering that point is equal to sum of the
currents leaving.
What is n in the equation I = nAve and what are its units?
Number density of free charge carriers m⁻³
What is A in the equation I = nAve?
Cross-sectional area of the conductor.
What is e in the equation I = nAve?
The elementary charge (1.6x10⁻¹⁹C)
What is v in the equation I = nAve?
The drift velocity of the charge carriers.
What is a conductor?
A material with a large number density of charge carriers ~10²⁸m⁻³
What is an insulator?
A material with a low number density of charge carriers.
, What is a semiconductor?
A material with an intermediate number density of charge carriers ~10¹⁷m⁻³
What is potential difference?
The work done per unit charge between two points
What is the SI unit for potential difference?
Volt (V)
What units are equivalent to the volt?
Joules per Coulomb (JC⁻¹ )
What is EMF (Electromotive force)?
The work done per unit charge supplied to the charge carriers
How is a voltmeter connected?
In parallel.
What is the resistance of an ideal voltmeter?
Infinite.
What is thermionic emission?
The emission of electrons from the surface of a heated metal.
What is the work done on an electron when it passes through a p.d. of V volts?
eV where e is the charge on the electron.
What is Ohm's Law?
For a metallic conductor at constant temperature the p.d. is proportional to current.
What is electrical resistance?
The opposition of an object to a flow of current through it.
How is resistance calculated?
V/I
What units are equivalent to an Ohm?
VA⁻¹
Why does resistance increases with temperature?
The amplitude of lattice ion vibrations increases causing more frequent collisions
between electrons and lattice ions, leading to the electrons doing more work as they
move through the wire.
Why does current flow lead to heating in components?
Electrons collide with the lattice ions and transfer some of their kinetic energy to the
lattice ion's vibrations.
What is an Ohmic conductor?
An object for which p.d. is proportional to current.
What is meant by the threshold pd of a diode?
The pd at which resistance starts to fall rapidly as pd increases.
What are the units of resistivity?
Ωm
What is ρ in R = ρL / A?
The resitivity of the material.
What is L in R = ρL / A?
The length of the wire.
What is A in R = ρL / A?
The cross-sectional area of the wire
As a metal gets hotter what happens to its resitivity?
