Electricity Flashcards
Electric Charge
Indicate if a body has an excess or a deficiency of electrons
Electrostatics
The properties of charge particles at rest
Negative charge
When an object gains electrons.
Polythene when rubbed a dry cloth
Positive charge
When an object loses electrons
Perspex when rubbed with a dry cloth
Point discharge
Where ions in the air either strongly attracted or appelled from the tip of a charged conductor and move towards or away from it
Coulomb’s law
The force between two point charges is directly proportional to the product of the charges at inversely proportional to the square of the distances between them
Electric field
The region of space in which electric forces can be felt
Electric field line
The line along which a positive charge would move if placed in the electric field
Electric field strength
Add a points in the electric field it is the force experienced per unit charged placed at that point in the field
E = F/Q
Potential difference (V)
The work done in moving a charge of one coulomb from 1point to another
V = W/Q
Insulator
A substance through which electric charge cannot flow
Conductor
A substance through which electric charge can flow
Coulomb
Unit for electric charge. One coulomb of charge passes a particular point when a current of 1 A flows for 1 second
1 Volt
The potential difference between two points if one Joule of work is done in bringing one coulomb of charge from one point to the other
Capacitance
The ratio of charge to voltage in a conductor
C = Q / V
Emf
Electromotive Force. The voltage applied to a circuit
Capacitor
An electrical device capable of storing electric charge
Farad
A capacitor has a capacitance of 1 farad, if by placing a charge of 1 coulomb on it raises it potential by 1 volt
1 F = 1 C/V
Resistance
The ratio of voltage across an object to the current flowing through it
R=V/I
Resistor
A device that converts electrical potential energy to some other form
Resistivity
A constant associated with resistance of a body. Equal to the product of the resistance of the body and its cross-sectional area divided by its length
Potential at a point
The difference in the potential at a given point and potential of the earth (take it to be 0)
Current
The rate of flow of charge
I = Q/t
Ammeter
A device that measures current. Must be connected in series
Voltmeter
Advice that measures potential difference across a component must be connected in parallel or across the component
AC vs DC
DC always flows in one direction, AC constantly changes direction
Ohm
Unit of resistance. Conductor has resistance of 1 ohm if a current of 1A passes through when a potential difference of 1V is applied
Ohm’s Law
The current flowing through conductor is directly proportional to the potential difference across it, if the temperature remains constant
V = IR
Joules Law
The rate of heat produced in a conductor is proportional to the square of the current flowing through it
Ion
An atom or group of atoms that has lost or gained one or more electrons
Electrolysis
The passing of an electric current true or liquid causing a chemical reaction
Fuse
A safety device consisting of a piece of wire which melts when a current above a preset value passes through it
MCB
Miniature circuit breaker. A safety device which breaks the circuit if it takes a current above a preset value
RCD
Residual current device. A safety device that breaks the circuit if it detects a current difference between live and neutral above a preset value
Radial Circuit
When a separate life and neutral wire are connected from the distribution box to an appliance which uses large current. E.g. electric cooker
Ring circuit
When the tree terminals of each socket (live, neutral and earth) are connected to three corresponding wires arranged in a ring or loop with each of the rings connect to the distribution box
Bonding
A safety precaution whereby all metal pipes taps and tanks are earthed
1 kWh
1 kilowatt hour full stop the amount of energy used by 1000 watt appliance in one hour
Semiconductor
A substance whose resistivity is between that of a good conductor and a good insulator. The resistivity decreases of the temperature increases
Holes
Positively charged gaps or spaces in a substance which are created when electrons break free from covalent bonds
Intrinsic conduction
Occurs in a pure semiconductor when there are an equal number of electrons moving from negative to positive and holes moving in the opposite direction. The movement of charge through a pure semiconductor
Doping
The addition of impurities to a semiconductor to increase its conductivity
Extrinsic conduction
An increased rate of conduction due to the addition of impurities. The movement of charge through a doped semiconductor
N-Type semiconductor
A semiconductor in which the impurity added produces more free electrons available for conduction
P-Type Semiconductor
Semiconductor in which the impurity added produces extra holes available for conduction
Diode (p-n junction)
A semiconductor device that allows current to flow in one direction only
LDR
Light dependent resistor. A semiconductor who’s resistance decreases as light intensity increases
Thermistor
A semiconductor whose resistance decreases rapidly with increasing temperature
Ampere
The constant current that, if maintained in two straight parallel conductors of infinite length, of negligible cross-section, and placed 1 meter part in a vacuum would produce a force on each conductor of 2 x 10-⁷ newtons per meter of length
Magnetism
A phenomenon by which certain metals exert attractive or repulsive forces on other metals
Magnetic field
A region of space in which magnetic forces can be felt
Magnetic Field line
Indicates the direction magnetic north would travel in the magnetic field if it was free to do so
Fleming’s left hand rule
If the thumb, index finger and second fingers are held it right angles to each other, with index finger pointing in the direction of the magnetic field and the second finger pointing in the direction of the current then the thumb points in the direction of the force
Magnetic flux
Total amount of magnetic field in a given region. Product of magnetic flux density and area
Magnetic flux density (B)
At a point in a magnetic field it is a vector whose magnitude is equal to the force experience by conductor of length 1 m, carrying a current of 1A, right angles to the field at that point and who’s direction is is the direction of the magnetic field lines
1 Tesla
The magnetic flux density at a point if a conductor of length 1 m, carrying a current of 1A, experiences of force of 1 N when placed at right angles to the field
1 Weber
The magnetic flux over an area of 1 m² if place in a field of magnetic flux density of 1 Tesla
Electromagnet
Consists of a solenoid with a soft iron core. When current is passed through the solenoid, the core becomes magnetic. When the current is switched off, the core loses its magnetism
Electromagnetic induction
The inducing of an EMF by changing the magnetic flux in a closed loop
Laws of electromagnetic induction
Lenz’s law
Faraday’s law
Faraday’s Law
The size of the induced EMF is proportional to the rate of change of magnetic flux linking the circuit
Lenz’s Law
The direction of an induced EMF opposes the change causing it
Mutual induction
Occurs in two adjacent coils when the magnetic field in one coil changes at an EMF is induced in the other
Self Induction
When a changing magnetic field in a coil induces an EMF in the coil itself
Transformer
An electrical device used to change the voltage of AC power supplies
Inductor
An electrical device used to induce a back EMF
Electrical generator
A device which converts mechanical energy to electrical energy by electromagnetic induction
