Charge and current Flashcards
What is electric current
The rate of flow of charge. Measured in amps
What is electric charge
A physical property like mass, either positive or negative. Measured in coulombs. Opposites attract, same charges repel.
What are the charge carriers in liquids
Ions
How to increase the current of a metal wire
Increase the area of the wire for more electrons to flow past. Increase the speed of the electrons so more flow past the same point in the same time interval.
What is an ammeter
An ammeter measures electric current in a circuit, placed in series where measurement is needed. It should have minimal resistance to accurately measure current without affecting it. An ideal ammeter has zero resistance, causing no change in the current it measures.
What is quantisation of charge
Quantisation of charge means that electric charge always exists only in multiples of the elementary charge e. It was introduced by physicist Robert Millikan through his oil drop experiment, confirming the quantized nature of charge.
What is a Liquid that can carry an electric current called
Electrolyte. They are ionic solutions, e.g Salt dissolved in water. If an anode (A positive electrode) and cathode (A negative electrode) are placed in an ionic solution, the negatively charged ions (anions) move towards the anode, and gives an electron to the anode. The positively charged ions (cations) move towards the cathode and take an electron from the cathode. This creates a flow of charge, which creates a current.
What is a conventional current
A current where the charge always flows from the positive to negative. Before discovery of electrons charge
What is the conservation of charge
Electric charge can not be created or destroyed. All electric charge in universe remains constant.
What is Kirchoffs first law
For any point in an electrical circuit, the sum of currents into that point is equal to the current out of it
What is number density
Number of free electrons per metre cubed. Materials with a number density of around 10^28 are conductors. Materials with number density around 10^17 are semiconductors. Materials with number density much lower than this are insulators.
Derive I=Anev
I = Charge / Time. Charge is defined as the electric charge flowing past a point in a material per second when there is 1 amp of current. In a conductor, the charge is produced by electrons, which have a charge of e. So the charge can be written as the number of electrons multiplied by the elementary charge multiplied by the volume of the conductor. When there is a current in the conductor, a certain amount of electrons pass a point per second. This can be written as the cross sectional area of the point multiplied by the mean drift velocity of electrons. Subbing into I = nev/t gives I = Anev
