Electricity Flashcards
literally fucking aids of a topic
Electric Charge
(Q or q), Indicates if a body has an excess or deficiency of electrons
Conductor
Any substance through which electric charge can flow.
Insulator
Any substance through which electric charge cannot flow
Point Discharge
The phenomenon where ions in the air are either strongly attracted or repelled from the tip of a charged conductor and move towards or away from it.
Coulomb’s Law
The electrostatic force between two point charges is proportional to the product of their charges and inveersely proportional to the square of the distance between them.
Electric Fields
The region of space in which electric charges at rest experience an electrostatic force.
Electric Field Lines
The line along which a positive charge would move if placed in the electric field.
Electric Field Strength
(E), the force per unit positive charge at a point
(N C^-1 or V m^-1)
Potential Difference
The work done in moving a charge of one Coulomb from one point to the other.
Electromotive Force
(emf) is the voltage that is applied to a cicuit.
Capacitance
The ratio of the charge on the capacitor to the poitential difference applied across it.
Capacitor
An electrical device capable of storing electric charge.
Electric Current
(I), The flow of electric charge.
Joule’s Law
The rate of heat production in a conductor is proportional to the square of the current; provided its resistance is a constant.
Fuse
A piece of wire that will melt when a current above a certain size passes through it.
Miniature Circuit Breakers
(MCBs), are safety devices used to prevent electrocution by fire by preventing too large a current flowing in the circuit.
They contain a bimetallic strip and an electromagnet.
They are advantageous over fuses becuase they operate faster and can be reset with a switch.
Residual Current Devices.
(RCDs), are trip switches that cut off current very quickly when a fault in an appliance causes a small current to flow to earth.
They serve the same purpose as an MCB but operate much faster and can be used when dealing with very small currents- therefore safer.
Resistance
(R), is the ratio of voltage across an object to the current through it.
Resistor
A device that converts electrical potential energy to some other form.
Ohm’s Law
Under constant physical conditions, the potential difference across a conductor is proportional to the current flowing through it.
Resistivity
(p), is the constant associated with the resistance of a body; it is equal to the product of the resistance of the body an its cross-sectional area divided by length.
Wheatstone Bridge
A device used to measure the resistance of an unknown resistor.
Advantages: More accurate than an ohmeter, multimeter or combination of an ammeter and voltmeter.
Disadvantages: Less compact or portable and takes more time to set up than an ohmeter, multimeter or combination of ammeter and voltmeter.
Semiconductor
A substance whose resistivity is between that of a good conductor and a good insulator.
Intrinsic Conduction
The movement of charge through a pure semiconductor
Extrinsic Conduction
The movement of charge through a doped semiconductor.
Doping
The addition of a small amount of another element to a pure semiconductor to increase its conductivity.
N-type Semiconductor
One in which the impurity added produces more free electrons available for conduction.
P-type Semiconductor
One in which the impurity added produces extra holes which are available for conduction.
Diode
A semiconductor device which allows current to flow in one direction only.
LDR
(Light-dependent resistor), is a semiconductor whose resistance varies from a high value in the dark to a lower value in bright light.
Thermistor
A semiconductor device whose resistance decreases rapidly with increasing temperature.
Magnetism
The phenomenon by which certain materials eert attractive or repulsive forces on other materials.
Magnetiv Fields
The region in space where magnetic forces can be felt.
Magnetic Field Lines
Indicates the direction a “magnetic north” would travel in a magnetic field is free to do so.
Magnetic Flux Density
(B), is the measure of the strength of the magnetic field.
Ampere
The constant current which, if maintained in two straugh parallel conductors of infinite length, of negligible cross section and placed one metre apart in a vacuum, would produce a force on each conductor of 2x10^-7 newtons per metre of length.
Electromagnetic Induction.
Where an emf is induces by a change in the magnetic flux linking a circuit.
Magnetic Flux
(Φ), is the total amount of magnetic field in a given region; it’s the product of magnetic flux density (B))= and area (A).
Faraday’s Law
The magnitude of the induced emf is proportional to the rate of change of flux linking a curcuit.
Lenz’s Law
The direction of the induced emg is always such as to oppose the change casuing it.
Alternating Current
(a.c), is an electric current whose direction reverses periodically due to an alternaating voltage,
Direct Current
(d.c.), is an electric current that flows continuously in the same direction.
Mutual Induction
Where a changing magnetic field in one coil induces an emf in another coil.
Transformer
An electrical device used to change the voltage of a.c. power supplies.
Self Induction
Where a changing magnetic field in a coil induces an emf in the coil itself.
Inductor
An electrical device used to induce a back emf.
