component 2 Flashcards
Efficiency of a system
% efficiency = (useful work out) / (work put in) X 100
Potential difference (pd), V
Potential difference is the difference in the amount of energy that charge carriers have between two points in a circuit.
Ohm’s law
The current in a metal wire at constant temperature is
proportional to the pd across it.
Superconducting transition temperature, Tc
The temperature at which a material, when cooled, loses all its electrical resistance, and becomes super-conducting. Some materials (e.g. copper) never become superconducting however low the temperature becomes.
The law of conservation of charge
Electric charge cannot be created or destroyed, (though positive and negative charges can neutralise each other). Charge cannot pile up at a point in a circuit.
Emf, E
The emf of a source is the energy converted from some other form (e.g. chemical) to electrical potential energy per coulomb of charge flowing through the source.
Capacitor
A capacitor is a pair of conducting plates separated by an insulator. If a potential difference is placed across the plates, they acquire equal and opposite charges.
Dielectric
Insulator between the plates of a capacitor, also serving to make the capacitance larger than if there were just empty space.
Hooke’s law
The tension in a spring or wire is proportional to its extension from its natural length, provided the extension is not too great (doesn’t exceed elastic limit)
Ductile material
A material which can be drawn out into a wire. This implies that plastic strain occurs under enough stress.
Elastic limit
This is the point at which deformation ceases to be elastic. For a specimen it is usually measured by the maximum force, and for a material, by the maximum stress, before the strain ceases to be elastic.
Brittle material
Material with no region of plastic flow, which, under tension, fails by brittle fracture
Newton’s law of gravitation
The gravitational force between two particles is proportional to the product of their masses, m1 and m2, and inversely proportional to their separation squared, r^2
Coulomb’s law
The electrostatic force, F, between two small bodies is
proportional to the product of their charges, Q1 and Q2, and inversely proportional to their separation squared, r^2.
Electric field strength, E
The force experienced per unit charge by a small positive charge placed in the field. This is a vector quantity.
Gravitational field strength, g
The force experienced per unit mass by a mass placed in the field. This is a vector quantity
Electric potential, VE
Electric potential at a point is the work done per unit charge in bringing a positive charge from infinity to that point. (scalar)
Gravitational potential, Vg
Gravitational potential at a point is the work done per unit mass in bringing a mass from infinity to that point. (scalar)
Black Body
A black body is a body (or surface) which absorbs all the electromagnetic radiation that falls upon it. No body is a better emitter of radiation at any wavelength than a black body at the same temperature.
Absolute or kelvin temperature
At 0 K (-273.15°C) the energy of particles in a body is the lowest it can possibly be
Boyle’s Law
pV is a constant : at constant temperature pressure and volume of a gas are inversely proportional
Charles’s Law
V/T is constant : at constant pressure the volume of a gas is directly proportional to temperature
Pressure Law
p/T is constant : at a constant volume the pressure of a gas is directly proportional to temperature
Brownian Motion
- particles suspended in a fluid move randomly as a result of collisions with fast randomly moving particles
- random motion is where particles have a range of speeds and no preferred direction of movement
Kepler’s laws of planetary motion: 1
Each planet moves in an ellipse with the Sun at its focus.
Kepler’s laws of planetary motion: 2
The line joining a planet to the centre of the Sun sweeps out equal areas in equal times.
Kepler’s laws of planetary motion: 3
T^2, the square of the period of the planet’s motion, is
proportional to r^3, in which r is the semi-major axis of its ellipse. [For orbits which are nearly circular, r may be taken as the mean distance of the planet from the Sun.]
Kirchoff’s first law
Kirchhoff’s current law (1st Law) states that current flowing into a node (or a junction) must be equal to current flowing out of it. This is a consequence of charge conservation.
Kirchoff’s second law
Kirchhoff’s voltage law (2nd Law) states that the sum of all voltages around any closed loop in a circuit must equal zero. This is a consequence of charge conservation and also conservation of energy.
sum of the EMF’s = sum of PD’s
Current
Current is the rate of flow of charge, and travels in the direction that a positive test charge would
