Alevel physics

Electric Current

Rate of flow of charge

Potential Difference

Work done per unit charge

Resistance

potential difference per unit current

Charge

A fundamental property of matter. Charged objects will experience a force when placed in an electric field.

Properties of a diode

Very high resistance in reverse bias. A very low resistance when p.d. across it is around 0.7V in forwards bias.

Property of an ideal ammeter

Zero resistance

Property of an ideal voltmeter

Infinite resistance

Units of potential difference

Volts, V

Units of charge

Coulombs, C

Units of current

Amps, A

Units of resistance

Ohms (Ω)

Units of resistivity

Ohm-metres (Ωm)

The effect of temperature on metal conductors

Increase in T leads to increase in resistance

The effect of temperature on thermistors

Increase in T leads to increase in resistance

Superconductivity

A property of certain materials which have zero resistivity at and below a critical temperature, which depends on the material

Applications of superconductors

Production of strong magnetic fields, reduction of energy loss in transmission of electric power

Effect of adding resistors in series

Increases circuit resistance

Effect of adding resistors in parallel

Reduces circuit resistance

Current in a series circuit

The same throughout

Voltage across components connected in series

Shared between the components. Components with larger resistances get greater share of the p.d.

Current in a parallel circuit

Splits at branches and recombines at end of branches. If branch has a larger resistance it gets less current.

P.d. across branches connected in parallel

Equal across each branch

Potential divider

Used to supply constant or variable p.d. from a power supply. Two or more resistors connected in series.

Light-dependent resistor

Component whose resistance decreases as the light intensity it is exposed to increases and vice versa

Terminal p.d.

P.d. supplied by a power supply or battery when a current is flowing

E.m.f.

The p.d. supplied by an ideal power supply (with no internal resistance). The maximum possible p.d. supplied by a power supply. Voltmeter reading across power supply when no current is flowing.

Angular Displacement

The angle an object in circular motion turns through

Angular Speed

The rate of change of angular displacement of an object in circular motion

Centripetal Force

The resultant force on an object that moves along a circular

Path difference

The difference in distance travelled by two waves

Coherence

Two (or more) waves with a constant phase difference and frequency, wavelength

Antinode

Point on stationary wave where two waves are in phase and constructive interference occurs. Has Maximum displacement.

Node

A point on a stationary wave where the displacement is always 0

Electric Potential

Work done per unit charge against the field to move a positive point charge from infinity to that point

Capacitor

A component which can store electric charge then release it

Time constant

The time taken for the charge or p.d. of a capacitor to fall by 63% of its original value

Relative permittivity

Ratio of charge stored by a capacitor with a dielectric between plates to charge stored without dielectric

Tensile stress

The tensile (stretching) force applied per unit of cross-sectional area perpendicular to the force

Tensile Strain

The extension per unit length

Elastic Strain Energy

The potential energy stored in an elastic material due to it being stretched or compressed. Energy stored is equal to the work done in stretching the spring

Breaking Stress

Largest tensile stress that can be applied before a material break

Brittle

A material that shows hardly any plastic deformation before breaking, or fracturing

Brownian Motion

the erratic random movement of microscopic particles in a fluid, as a result of continuous bombardment from molecules of the surrounding medium

Relative molecular mass

the ratio of the average mass of one molecule of an element or compound to one twelfth of the mass of an atom of carbon-12

Specific Heat Capacity

The amount of energy needed to raise the temperature of 1kg of the substance by 1K (or 1C)

Specific latent heat of fusion

The quantity of thermal energy required to change the state of 1kg of a substance (solid to liquid) without a change in temperature

Internal Energy

The sum of the randomly distributed kinetic and potential energies of all its particles

Couple

a pair of forces of equal size with act parallel to each other, but in opposite direction.

Gravitational Potential

Work done per unit mass to move an object from infinity to that point

Potential gradient

change in potential per metre

Gravitational field strength

force per unit mass in a uniform gravitational field

G

gravitational field constant (6.67×10^-11 )

Photoelectric effect

emission of electrons from the surface of a metal in response to incident light

Photon

A 'quanta' (smallest discrete unit) of light

Wave-particle duality

the concept that both light and matter exhibit properties of both waves and particles

Transverse wave

a wave which oscillates perpendicular to the direction of propagation.

Longitudinal

A wave which oscillates parallel to the direction of propagation

Wavelength

Distance between two consecutive points on a wave that are in phase

Meson

A type of hadron with a quark-antiquark pair

(e.g. pions, kaons)

Baryon

A type of hadron with 3 quarks

(e.g. protons, neutrons)

Quark structure of a proton

uud

Quark structure of a neutron

udd

Ohm's Law

Provided that temperature and other physical conditions remain constant, the current through a conductor is directly proportional to the potential difference across the conductor

Resistivity

A measure of how strongly a material opposes or resists the flow of current

Pressure law

At constant volume, the pressure of a gas is directly proportional to its absolute temperature

Avagadro's constant

The number of molecules in one mole of a substance

Boltzmann Constant

Amount of energy corresponding to the random thermal motions of particles making up a substance

Hooke's Law

The extension of a spring is directly proportional to the force exerted on it, so long as the elastic limit is not exceeded.

Elastic limit

If a spring is stretched beyond this point, it will not return to its original length when the external forces are removed

Spring constant

A measure of the stiffness of a spring.

Breaking stress

The largest tensile stress that can be applied to a material before it breaks

Significance of area under a graph of force vs extension

Equal to the energy stored in the stretched or compressed object

Elastic behaviour

After a stretching force is removed, object returns to its original length

Plastic behaviour

After a stretching force is removed, object remains deformed

Ductile behaviour

Object undergoes large plastic deformation before breaking, once passing its elastic limit

Brittle behaviour

Object undergoes very little or no plastic deformation before breaking, once passing its elastic limit

Elastic strain energy

Energy stored in stretched or compressed objects that can be used to do work. It is equal to the work done in initally stretching or compressing the object.

Young modulus

stress/strain. Measured in Pa.

Strong materials

Have a large breaking tensile stress

Tough materials

Can absorb a lot of energy before they break

Scalar

A quantity with only magnitude

Examples of scalars

Speed, distance, energy, temperature, mass

Examples of vectors

Displacement, velocity, acceleration, force, momentum

Moment of a force

The force multiplied by the perpendicular distance from the pivot to the line of action of the force

Moment of a couple

Force x perpendicular distance between the lines of action of the forces

Principle of moments

For a pivoted object in equilibrium, the sum of the clockwise moments about any point = the sum of the anticlockwise moments about the same point

Centre of mass

The point at which the mass of an object can be assumed to be concentrated.

Point through which a single force on the body has no turning affect

Displacement

The shortest distance between two points

Acceleration

The rate of change of velocity

Gradient of a displacement-time graph

Velocity

Gradient of a velocity-time graph

Acceleration

Area under a velocity-time graph

Displacement

Gradient of tangent to point on displacement-time graph

Instantaneous velocity

Tangent to point on velocity-time graph

Instantaneous acceleration

Cause of frictional forces

The force acting between two solid surfaces in relative motion across each other due to surfaces not being perfectly smooth

Cause of drag forces

Collisions between moving object and particles that make up the fluid (liquid or gas) that the object is travelling through.

Terminal speed

The maximum possible speed an object can attain, reached when the force propelling it is balanced with the drag forces acting on it

Relationship between air resistance and speed

Air resistance increases with speed, as the frequency of collisions between object and fluid particles increases and the average force exerted in each collision also increases.

Factors that affect the top speed of a vehicle

How streamlined it is; maximum power of engine; viscosity of fluid it is travelling through etc

Effect that air resistance has on the trajectory of a projectile

It decreases the maximum vertical height reached and the maxium horizontal distance travelled