Electricity Flashcards
Revision
What is electricity and how is electrical energy transferred?
Electricity is the flow of electrons through a conductor from negative to positive terminals.
Electrons transfer electrical energy.
What is an electrical current?
A flow of charged particles.
What is Kirchhoff’s second law?
The sum of the potential rises and falls around a closed path in a circuit is zero”
What is Kirchhoff’s first law?
The total current flowing into any point in a circuit is equal to the total current out of that point
What are the effects of an electrical current?
A magnetic field is induced
Chemical changes can occur
A temperature rise in the conducting material
What is the unit of charge?
Coulombs (C)
A current of 12A passes through a kettle for 20s. How much charge has flowed through the kettle?
q =It = 12 x 20 = 240C
A charge of 200C flows through an iron for 10s. What is the current?
q=It, I= q/t = 200/10 = 20A
What is an ohmic conductor?
Conductors for which I-V graphs are straight lines are said to be ohmic conductors. The current will change proportionately with the voltage.
Resistance of a uniform conductor depends on:
- Its length (l)
- Its cross sectional area (A)
- The material that it is made from
What is potential difference?
The potential difference between two points in a circuit is the energy required to transport a unit charge between those two points.
It is measure in volts.
What are acceptable units for current?
Amps (A)
Coulombs per second
How does charge flow through a metal?
A metallic solid has a very regular lattice array of atomic nuclei and the outermost electrons of each atom are quite easily able to move throughout this lattice array. This type of arrangement is called metallic bonding. Metals are called good electrical conductors as any charge placed on them is free to move through
the lattice. We say that the mobile charge carriers are the electrons.
Why do insulators not allow charge to flow easily?
Substances that do not allow free charge movement, or whose atomic electrons are not free to move, are called insulators . The most common insulators used to prevent the flow of electric charge are rubber, plastics, paper, glass and ceramics. Charges placed onto any conductor will be free to evenly distribute over the surface of the conductor, whereas charge placed onto the surface of any insulator will stay in the same place.
What is conventional current?
conventional current is the motion of positive charges from the positive terminal of a battery to the negative terminal. This is the convention that is used and, although physically incorrect, is accepted as the international convention.
Electron flow is the direction of electron motion in a conductor negative to positive. One amp of conventional current in one direction is the same as one amp of electron flow in the opposite direction.
How do you calculate the total resistance of a number of resistors in a series circuit?
V(T) = V(1) + V(2) + V(3)
Using Ohms Law, V = IR
IR(T) = IR(1) + IR(2) + IR(3)
The current (I) cancels as it is the same through the whole circuit, leaving:
RT = R1 + R2 + R3
