Physics Adefinitlons and usefulfacts sheet
Electricity
Electric current is the rate of flow of charge. Potential difference is the work done per unit charge.
Ohm's Law: current is proportional to the potential difference as longas temperature is constant.
T h e emf of a cellis the electrical energy supplied per unit charge passing through it.
T h e critical temperature of a superconductor is the temperature below which it will have a resistivity
of zero.
T h e resistance of an LDR goes down as the light level increases.
The resistance of a thermistor goes down as the temperature increases.
Quantum and Particle Physics
The work function is the minimum energy required to release an electron from the surface of a metal
(not an atom!)
The threshold frequency is the minimum frequency (not energyl) of radiation needed to release an
electron from the surface of a metal (not an atoml)
The electron volt is the energy gained by an electron when it is accelerated through one volt.
T h e specific charge of a particle = Charge/ mass
Two isotopes of an element have the same number of protons but different numbers of neutrons.
T h e ionisation energy is the minimum energy required to take an electron from the zround state to
completelyfree oftheatom.
Learn: Workfunction = Planck's constant x threshold frequency hfo
Materials
Density is the mass per unit volume of a material.
Hooke's Law is "the extension of a material is proportional to the laad on it up to the imit of
proportionality".
Stressis the ratlo of load to crosssectionalarea. Strain is the ratio of extension to original length.
Tensile stress and strain is where the load is stretching.
The Young Modulus is the ratio of tensile stress totensile strain in the Hooke's Law region
A material is Elastic if it returns to its original shape when a load is removed or plastic if it is
permanently deformed when the load is removed.
The elastic limit of a wire is the maximum force which can be applied without the wire being
permanently deformed.
Abrittle material breaks with no plastic deformation- A ductile material has significant plastic
deformation before breaking
A stiff material has a small extension when a load is put on it. A strong material has a high breaking
stress (also called ultimate stress)
Energy stored in a material is the area under a Force- extension Eraph.
Mechanics
The conditions for an object to be In equilibrium with three coplanar forces on It are
a) The vector sum of the forces is zero.
b) The sum of the components of the forces in any two perpendicular directions is zero.
)The lines of actions of the forces all go through one point.
d) Principle of moments (see below)
Electricity
Electric current is the rate of flow of charge. Potential difference is the work done per unit charge.
Ohm's Law: current is proportional to the potential difference as longas temperature is constant.
T h e emf of a cellis the electrical energy supplied per unit charge passing through it.
T h e critical temperature of a superconductor is the temperature below which it will have a resistivity
of zero.
T h e resistance of an LDR goes down as the light level increases.
The resistance of a thermistor goes down as the temperature increases.
Quantum and Particle Physics
The work function is the minimum energy required to release an electron from the surface of a metal
(not an atom!)
The threshold frequency is the minimum frequency (not energyl) of radiation needed to release an
electron from the surface of a metal (not an atoml)
The electron volt is the energy gained by an electron when it is accelerated through one volt.
T h e specific charge of a particle = Charge/ mass
Two isotopes of an element have the same number of protons but different numbers of neutrons.
T h e ionisation energy is the minimum energy required to take an electron from the zround state to
completelyfree oftheatom.
Learn: Workfunction = Planck's constant x threshold frequency hfo
Materials
Density is the mass per unit volume of a material.
Hooke's Law is "the extension of a material is proportional to the laad on it up to the imit of
proportionality".
Stressis the ratlo of load to crosssectionalarea. Strain is the ratio of extension to original length.
Tensile stress and strain is where the load is stretching.
The Young Modulus is the ratio of tensile stress totensile strain in the Hooke's Law region
A material is Elastic if it returns to its original shape when a load is removed or plastic if it is
permanently deformed when the load is removed.
The elastic limit of a wire is the maximum force which can be applied without the wire being
permanently deformed.
Abrittle material breaks with no plastic deformation- A ductile material has significant plastic
deformation before breaking
A stiff material has a small extension when a load is put on it. A strong material has a high breaking
stress (also called ultimate stress)
Energy stored in a material is the area under a Force- extension Eraph.
Mechanics
The conditions for an object to be In equilibrium with three coplanar forces on It are
a) The vector sum of the forces is zero.
b) The sum of the components of the forces in any two perpendicular directions is zero.
)The lines of actions of the forces all go through one point.
d) Principle of moments (see below)
