Physics Module 4 Electric Circuits Flashcards
- Charge
Q. Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two-types of electric charges; positive and negative (commonly carried by protons and electrons respectively).
- Elementary Charge
The elementary charge is ± 1.6 x 10-19 C.
- Coulomb
C. Unit of charge.
- Electric Current
I. Rate of flow of charge. I = ΔQ / Δt.
- Ampere
A. Amp. Unit of current. The current is 1 ampere when 1 coulomb flows in 1 second. Coulomb per second.
- Quantise
Form into ‘quanta’. Restrict the number of possible values of (a quantity) or states of (a system) so that certain variables can assume only certain discrete magnitudes. For example, photons.
- Discrete
Discrete in science is the opposite of continuous: something that is separate; distinct; individual. For example in quantum theory, discrete may refer to discrete quanta.
- Conventional Current
Conventional Current flows from + to –. Conventional means ‘based on or in accordance with what is generally done or believed’.
- Electron Flow
Electrons flow from – to +.
- Kirchhoff’s First Law
Sum of or total current into a junction equals the sum of or total current out of a junction. Charge is conserved.
- Conservation
The principle by which the total value of a physical quantity or parameter (such as energy, mass, linear or angular momentum) remains constant in a system which is not subject to external influence.
- Mean Drift Velocity
v. The average displacement/distance travelled of the electrons along a wire per second. They move slowly in one direction through the (copper) lattice when there is a p.d. and collide constantly/in short distance with the lattice; measured in ms-1.
- Number Density of Charge Carriers
n. The number of electrons per unit volume, m-3.
- Conductors, Semiconductors and Insulators
Conductors, semiconductors and insulators are distinguished by their number densities. Conductors ~ 1028 m-3; semiconductors ~ 1017 m-3; insulators ~ 0 m-3
- P.d
V. P.d or potential difference is the work done per unit charge, measured in volts. Energy is transferred from electrical into other forms. V = W / Q.
- Volt
V. Unit of voltage or p.d. or e.m.f. The voltage is 1 volt when energy of 1 J is transferred per coulomb of charge. Joule per coulomb.
- E.m.f
E. E.m.f or electromotive force is the work done per unit charge, measured in volts. Energy is transferred from other forms into electrical. E = W / Q.
- Resistance
R. Voltage per unit current. R = V / I.
- Ohm
Ω. Unit of resistance. The resistance is 1Ω when a 1 V supply pushes a current of 1 A. Volt per ampere.
- Ohm’s Law
The voltage across a conductor is proportional to the current flowing through it; as long as other conditions like temperature remains constant. Shown by a straight line through the origin on an IV graph.
- Ohmic and Non-Ohmic
A component that obeys Ohm’s Law is ohmic. A component that does not obey Ohm’s Law is non- ohmic.
- Resistivity
ρ. Resistivity = ( Resistance x Cross Sectional Area ) / Length. Ω m.
Electrical resistance of a conductor of unit cross-sectional area and unit length. R = ρ L / A.
- Temperature
T. A measure of the average kinetic energy of the particles in a system. Adding heat to a system causes its temperature to rise. Temperatures are commonly measured in the Kelvin or Celsius scales.
- NTC
‘Negative Temperature Coefficient’. An increase in temperature causes a decrease in another variable such as resistance.